Table of Contents—Complete

To supply the need for edible oil, a huge industry has developed. The methods used to grow and process oil are based upon profit, not a healthful product. To choose more healthful oils, we need to look carefully at processing techniques. The healthiest oils are unrefined, crude oils. The healthiest oils are organically produced to avoid the solvent hexane, genetically modified plants, and pesticide residues.

The vast majority of the oils sold in developed countries are genetically modified, bleached, and heated to high temperatures. The result of oil refining is an oil that has been stripped of many nutrients such as beta-carotene, vitamin E, chlorophyll, and lecithin. Refined oils can be compared to white flour, which is also stripped of many important nutrients. These oils are then bottled in plastic bottles that can leach dangerous chemicals into the oil. Glass bottles are superior, but reduce profits.

The uses of fats and oils

Fats and oils are widely used to stop food from sticking during cooking. About 50 million tons of edible oil are produced yearly. For frying, sautéing, or baking, the non-stick abilities of fats and oils are appreciated. Many recipes call for oil, butter, or shortening. Fats and oils in food provide a feeling of satisfaction. The fast food and snack industries use vast amounts of frying oils. While salad dressings can be made in the blender with nuts, seeds, or avocados, most people buy commercial salad dressings, and most salad dressings contain oils.

How oil used to be made

In the old days cooking oil was made in small amounts using primitive presses. In Europe a wedge press was used to extract flax oil. The cook would hammer a wedge into a special wooden block filled with ground flax seeds. The oil would slowly drip out—often just enough for one day. This rich, golden oil was unheated and full of all the nutrients originally in the oil of flax seeds. There was no problem with the delicate oil becoming rancid as the flax seeds were ground and pressed on the same day. Folklore of the day had the wisdom not to expose this delicate oil to light or heat.

In many parts of Asia, palm oil has traditionally been squeezed out of the fruit of oil palms. In traditional palm oil extraction, the fruit is first steamed to soften the pulp. Using a mortar, the fruit is pounded to separate the fleshy part from the nut. A screw press has traditionally been used to separate the oil from the fiber. The oil is red in color because of the high beta-carotene content. Once the oil is separated, it is lightly heated to remove the excess water and then filtered before bottling. Sometimes the oil is allowed to separate to obtain the clearer oil at the bottom. The oil may be bottled in tinted or opaque bottles and can remain fresh for six months to a year. The small presses that historically made this pure, cold-pressed oil cannot now compete in price with the low-priced oils from a modern oil factory.

Modern oil processing

Bottled oil today is made in huge factories. In order of amount of production for food use, the major vegetable oils are soybean, palm, cotton, peanut, sunflower, canola, sesame, corn, olive, palm kernel, coconut, and flax. There are different ways of calculating the relative amounts of these oils. Palm oil may be one of the most exported oils in the world.

The technology of removing the most oil from any seed or bean is highly developed. Techniques for removing oil are based upon profit with little consideration of health consequences.

Crude vegetable oils are mainly made up of about 95% triglycerides. There are also some free fatty acids, monoglycerides, and diglycerides. Crude oils also contain variable amounts of phospholipids, sterols, squalene, triterpene alcohols, tocopherols and tocotrienols, carotenes, and chlorophyll. Some crude oils contain hydrocarbons. Hydrocarbons can come from atmospheric contamination or from the smoke of drying fires, especially with dried coconut.

Crude oils can have traces of metals, oxidation products, and undesirable flavors. Refining procedures have been developed to convert the crude oil into a bland product that is clear and has a long shelf life. Some of these components, such as hydrocarbons, should be removed. Other components are valuable as antioxidants or for nutrition.

Changing the seeds

Most of the oil seed crops grown today have been altered to increase the profits of the oil industry. Many have been altered with hard radiation or mutagenic chemicals in a process called selective mutation. Food oils that are made from seeds that have been mutated include canola oil, soybean oil, flax oil, and sunflower oil. Even if you choose an oil that is organic, it is allowed to be a product of selective mutation.

Figure 1 Some oils have not been genetically engineered or mutated

Text Box: Some oils have not been genetically engineered or mutated:
Olive oil
Palm oil
Peanut oil
Safflower oil.

Some oil seeds have been altered with genetic engineering. This can involve injecting genes from different plants or even genes from animals. Soybeans and corn have been genetically engineered to be more tolerant of a pesticide. Cottonseed has also been genetically engineered. Certain varieties of Canola have been genetically engineered as well. We are not sure if selective mutation or genetic alterations create seeds that are dangerous to human health. If you choose an organic oil, it is not allowed to be genetically engineered.

Figure 2 Some genetically engineered oils

Text Box: Some genetically engineered oils:
Soybean oil
Corn oil
Cottonseed oil
Canola oil (certain varieties)

Cold pressed oils

The term cold pressed is sometimes used to describe an extraction process of oils. This term applies to extraction using a hydraulic press or a screw press where the seeds, fruit, or beans are not heated before pressing. Cold pressed oils are more costly to manufacture and are usually found only in health food stores. Olive oil, palm oil, and sesame oil are the oils most often produced with cold pressing. If heat is used, the oil should be described as pressed, rather than cold pressed.

Preparing the seeds, beans, or grains for processing

The oilseeds are cleaned and dried before processing. Many seeds, such as soybeans are hulled to increase the oil and protein content and reduce fiber content. A common process is called flaking where the oilseeds are flattened to one-hundredth of an inch (0.3 mm). Heating of the oilseeds prior to oil extraction is common.

Expeller pressed oils

In modern oil factories it is common for oils to be expeller pressed. An expeller is a screw press with a constantly rotating shaft. The expeller press exerts great pressure on the ground seeds or beans, creating temperatures between 200 and 250 degrees Fahrenheit (93-121 C). These temperatures result in varying degrees of rancidity, depending on the seed or bean being pressed. Seeds or beans with a higher content of essential fatty acids, such as canola and soybean, are more susceptible to rancidity. Natural antioxidants in oils may reduce their susceptibility to rancidity.

Typical expeller pressing operations involve cooking, pressing, cake cooling, and oil filtration. Some oils such as olive oil and evening primrose oil may be sold without further processing. The pressed out "cake" may be further processed by solvent extraction.

Hexane extraction of oils

When you buy a bottle of oil, the list of ingredients does not tell how the oil has been processed. Oil seeds are first prepared for pressing. The seeds, grains, or beans are ground up. Some seeds can be pressed without solvents. Coconut oil, palm oil, cocoa butter, virgin olive oil, and sesame oil are not normally extracted with the solvent hexane. Other oils are routinely extracted using the solvent hexane. These include soybean oil, flax oil, canola oil, peanut oil, safflower oil, corn oil, and cottonseed oil. About 98% of the soybean oil used in the United States is produced using hexane as a solvent. Some olive oil is made with the solvent hexane, but not extra virgin olive oil.

Figure 3 Oils not normally extracted with the solvent hexane

Text Box: Oils not normally extracted with the solvent hexane:
Coconut oil
Palm oil
Cocoa butter
Virgin olive oil
Sesame

When oils are extracted using hexane as a solvent, the ground up seeds or beans are bathed in hexane for 30-45 minutes. This immersion in hexane is normally done at a temperature of 304 Fahrenheit (150 C). The hexane increases the amount of oil extracted. Typically, two tons of hexane is used to extract the oil from one ton of ground up and pressed seeds or beans. The hexane is carefully removed from the oil because it can be explosive during storage and shipping.

The hexane that is not lost to the air, the oil, or the mash is reused. Residues remain both in the oil and in the leftover pressed seed mash. The leftover pressed mash is valuable for animal feed, as it is a high protein product. The leftover dried mash is also used to make textured vegetable protein, used in many products designed for human consumption. There is some concern that these products, especially those with soybean protein, may have hexane residues.

Figure 4 Oils routinely extracted with the solvent hexane

Text Box: Oils routinely extracted with the solvent hexane:
Soybean oil
Flax oil
Canola oil
Peanut oil
Safflower oil
Corn oil
Cottonseed oil

It is well documented that hexane is toxic to nerves (OSHA, 2009). It can also act to mutate human babies. For these reasons the European Union has set a residue limit for hexane in any food product of five parts per million. Canada has set a limit of ten parts per million. The United States has not set an upper limit for hexane contamination of food products. You may be wondering how much hexane has been found in cooking oils. The lowest levels reported in edible oils are about one part per million hexane. Other tests on palm kernel oil, soybean oil, and peanut oil indicate that it is not abnormal for food oils to have 100-1500 parts per million of hexane (FAO/WHO, 1970). This can be 100 times the limits for hexane residues mentioned. Neither the oil producers nor the United States government test oils for their residual hexane content. You can avoid hexane residues by buying organically produced oils or by using oils such as extra virgin olive oil. The healthiest way to avoid hexane is to get your fats and oils directly in food.

The loss of lecithin: degumming

Many crude vegetable oils contain phospholipids. These phospholipids are an important part of the nutrition of these oils. A few oils contain significant amounts of phospholipids. Soybeans contain about 3% phospholipids, mainly lecithin. Lecithin is an important source of phosphatidylcholine, one of the phospholipids. Other important phospholipids found in crude vegetable oils are phosphatidylethanolamine and phosphatidylinositol. Canola oil contains about 2.5% phospholipids, while sunflower oil contains about 1.5%. The content of phospholipids in corn oil varies from 5.2% to 8.7%. Some oils such as palm oil contain very little phospholipids.

Manufacturers take out the phospholipids in a process called degumming. This is done to extend shelf life, improve clarity, and to aid the refining process. The removed phospholipids are sold to be used in the manufacture of lecithin and as emulsifiers.

Removing these phospholipids degrades the nutrition of these oils. This is one example of an important nutrient being removed from refined oil to increase profits, despite the fact that it lowers the nutritional value of the oil. You can avoid these degummed oils by eating your fats and oils directly in food or by using unrefined oils.

Caustic refining

Caustic refining is used to remove "impurities" in vegetable oils. Caustic soda is added to the oil in this refining step. Caustic soda is also known as Sodium hydroxide or lye. On a positive note, caustic refining also contributes significantly to the removal of contaminants such as aflatoxin and organophosphate pesticides.

Polycyclic aromatic hydrocarbons, if present, must be removed by activated carbon treatment. The polycyclic aromatic hydrocarbons are often introduced into the oils through atmospheric contamination or from the smoke of drying fires. They are reduced by half during oil refining—one of the few healthful effects of oil processing (Bailey, 2005).

If these impurities in the vegetable oils are not removed, the oils, when heated in subsequent steps may turn dark, smoke and foam, or become cloudy from the precipitation of solids. Many of these impurities are important nutrients.

Bleaching of edible oils

Bleaching is done to remove any color from oils. Bleaching of oils is not done with chlorine bleach; a clay is used. The clay absorbs "impurities" such as chlorophyll. Bleaching is often done at temperatures of 275 Fahrenheit (135 C). Bleaching may involve acid pretreatment. After a retention period, the clay is removed along with the absorbed materials. Bleaching is a normal part of edible oil processing and is especially needed if the oil is to be hydrogenated.

Hydroperoxides are undesirable contaminants introduced by the high heat of prior processing. Bleaching may remove some of the oxidation products such as hydroperoxides, thus extending shelf life of the bottled oil.

The major color pigments in edible oils are chlorophyll and carotenoids. For high-chlorophyll seeds, such as canola, bleaching clay dosing is quite heavy and is sometimes augmented by the addition of activated carbon. Carotenoids such as beta-carotene (pro-vitamin A) are important antioxidants. Crude palm oil contains a mix of carotenoids with both alpha-carotene (33%) and beta-carotene (55%). Beta-carotene is an important fat-soluble vitamin that is removed during bleaching.

Chlorophyll is a healthful nutrient and a good source of magnesium. Chlorophyll is intentionally removed during bleaching to obtain a uniform clear color. Trace metals such as iron and copper are also largely removed during bleaching. Polyphenols are important antioxidants that are removed during the bleaching process. The removal of these important nutrients may produce a clear oil with a longer shelf life, but it reduces the nutrition of the edible oils.

Figure 5 Nutrients eliminated during bleaching of oils

Text Box: Nutrients eliminated during bleaching of oils:
Chlorophyll
Beta-carotene
Iron
Copper
Antioxidant Polyphenols

Dewaxing

Some edible oils have waxes that are removed to improve the appearance of the finished product. Corn, sunflower, and canola have waxes that are routinely removed. Waxes are removed by a chilling, settling, and separation process.

Hydrogenation

The oil refining steps prior to hydrogenation remove impurities in the crude oil. Partial hydrogenation changes the melting point and eliminates some of the unsaturated fatty acids. Partial hydrogenation is famous for creating trans fatty acids.

One reason to hydrogenate an oil is to increase its melting temperature. Both saturated fatty acids and trans fatty acids have higher melting temperatures than similar length natural cis unsaturated fatty acids. Natural cis oleic acid is 18 carbon atoms long and melts at 56 degrees Fahrenheit (13 C)—well below body temperature. Trans-oleic acid is also 18 carbon atoms long and melts at 113 degrees Fahrenheit (45 C)—above body temperature. Stearic acid is also 18 carbon atoms long and is fully saturated. Stearic acid melts at 157 degrees Fahrenheit (69 C)—well above body temperature.

Figure 6 Hydrogenation changes melting temperatures

Text Box: Hydrogenation changes melting temperatures:
Oleic acid melts at 56 degrees Fahrenheit (13 C)
Trans-Oleic acid melts at 113 degrees Fahrenheit (45 C)
Stearic acid melts at 157 degrees Fahrenheit (69 C)

Increased melting temperatures of fats enable fried products to be more crisp and baked products firmer. Increased melting temperatures allow a solid margarine or shortening to be made from cheap liquid oils.

Another reason to partially hydrogenate oils is to increase saturation while reducing unsaturated fatty acids. Monounsaturated fatty acids such as oleic acid are transformed into the saturated stearic acid or into trans fatty acids. Essential fatty acids are changed into less unsaturated fatty acids, trans fatty acids, or saturated fatty acids. When oils are used for frying for extended periods, the reduced unsaturated fatty acids from partial hydrogenation reduces rancidity. This extends the time the oil can be used for frying without undesirable tastes and smells. This increases profits for the fast food industry and the oil processing industry.

There are different degrees of hydrogenation. Brush hydrogenation is used to saturate just a few of the polyunsaturated fatty acids, primarily alpha-linolenic acid, to reduce undesirable flavor changes from heating oils. Brush hydrogenation is often used on soybean and canola oils to reduce their content of the triply-unsaturated alpha-linolenic acid. Unfortunately, this reduces the amount of the much-needed alpha-linolenic acid in the diets of people who consume this oil.

Oils can be fully hydrogenated. With full hydrogenation, there are no more unsaturated fatty acids. They have all been converted to saturated fatty acids, mostly stearic acid, with the addition of hydrogen. This produces a very hard fat that can be mixed with softer fats to produce margarines and shortenings without trans fatty acids. In a process called interesterification, fatty acids are swapped between triglycerides to make a uniform consistency. Unfortunately, this creates a highly saturated oil, increasing the risk of heart and arterial disease.

Normally, oils are partially hydrogenated. The degree of hydrogenation depends on the starting oil and the intended use. Hydrogenation is done in a pressure reactor at a pressure of about three atmospheres. The temperatures range above 284 degrees Fahrenheit (140 C), often 400 degrees Fahrenheit (204 C). Lower temperatures and less trans fatty acid production can be achieved with more expensive catalysts such as platinum. However, since profit is the only motive, higher temperatures and a cheap nickel catalyst are used, even though this produces more trans fatty acids. To remove the nickel catalyst, the oil may be mixed with bleaching clay and filtered. The bleaching clay helps to remove a green color that may result from residual nickel.

Winterization

Winterization keeps oils clear in the refrigerator. It is commonly done to partially hydrogenated soybean oil and palm oil. Wet winterization uses a solvent such as acetone or hexane. Dry winterization separates the various fractions based on differences in crystallizing temperatures.

Deodorization or physical refining

Typically the last step in the edible oil refinery is deodorization or physical refining. These processes are included in almost every refining operation. The high heat used in prior operations results in unpleasant odors and tastes from oxidation of the oils. These processes reduce unpleasant odors imparted by hydrogenation and other steps of oil processing. These last steps increase shelf life.

The process uses high heat and a low pressure. Free fatty acids and volatiles are removed, leaving triglycerides. Typical heats involved are 356-500 Fahrenheit (180-260 C). This amount of heat will result in rancidity, oxidation products, polymerization, and lowered amounts of vitamin E.

One of the unhealthy effects of such high heat on edible oils is polymerization. Physical refining can raise the level of polymeric glycerides by about 1% (Farrari, 1996).

The high heat of physical refining creates trans fatty acids even without hydrogenation. The level of trans fatty acids in corn, soybean, and canola oils increased to a substantial extent (1–4%) after physical refining (Farrari, 1996).

Plant sterols are a desirable component of edible oils. Refined oils have 18–36% less of the plant sterols compared with the crude oils. On the other hand, pesticides are an undesirable component of edible oils. Agricultural pesticides are often reduced during deodorization and physical refining.

Vitamin E lost in oil processing

Vitamin E is needed in edible oils to stabilize them during storage. Vitamin E is also needed by the people who consume the oil. In both cases, the greater the content of polyunsaturated fatty acids in the oil, the greater the need for vitamin E—in the bottle and in the body.

Vegetable oils and the products made from them usually contain large amounts of vitamin E, especially the alpha, beta, and gamma tocopherols. In addition, certain vegetable oils, particularly palm oil and rice bran oil, are rich sources of tocotrienols. Tocotrienols are a form of vitamin E that has weak vitamin E activity in the body, but provides stability against oxidation of the oil in the bottle.

The level of total tocopherols and tocotrienols decreased by about half after complete refining of corn oil and by about one-third in soybean and canola oils. The process of deodorization, with its high temperatures, caused the most reduction of vitamin E (Farrari, 1996).

Why is any vitamin E left after these high temperatures? Some of the vitamin E in these oils is in an esterified form. In the esterified form, vitamin E does not possess antioxidant properties and so is less sensitive to heat. The esterified forms of vitamin E does not protect the oils in a bottle from oxidation. Inside our bodies, the esterified form can be converted to the active form of vitamin E.

Chemicals leaching into oils from bottles

Approximately 70-80% of food packaging in in the form of plastic. The plastic can contain up to 60% of a plasticizer, such as polyvinyl chloride (PVC). Vinyl chloride is a known human carcinogen. Polyvinyl chloride has been strongly linked to liver cancer (Hui, 2006). In a study of edible oils packed in PVC bottles, 34% of the oils tested were found to contain vinyl chloride (Carter, 1977).

The most commonly used plasticizer for PVC is phthalate. Phthalates have structural similarities to thalidomide, which caused so many malformed babies. Phthalates have fetotoxic and teratogenic properties; they are toxic to fetuses and cause birth defects. Plasticizers migrate very well into fatty substances such as refined edible oils.

Polyethylene terephthlate (PET) is a common plastic used for bottles to package edible oils. Two PET monomers mono-ethylene glycol and di-ethylene glycol (antifreeze) can migrate into edible oils from the bottles. These glycol monomers can cause vomiting, respiratory failure, coma, and death (Hui, 2006).

Although plastic bottles are cheap, clear, and durable, refined oils are best packaged in darkened glass or metal containers.

Fake fats

There are many ways to alter fats and oils into forms not found in nature. These synthesized oils may be created for infant formulas, to reduce trans fats in spreads, to reduce obesity from overeating fats, or to increase the profits of food companies.

Interesterification

Triglycerides are the common form of fat where three fatty acids are attached to a glycerol backbone. In the industrial process called interesterification, the three fatty acids are stripped off of the glycerol backbone. This stripping is often done with microbial lipases. Next, these fatty acids are replaced (re-esterified) onto glycerol backbones. This allows manufacturers to change the physical properties of the oils. These “tailored fats” have rearranged fatty acids on the triglycerides. One example is when lard is made smoother because the fatty acids become uniformly distributed.

Spreads can be made from oils using interesterification. Part of the oil is fully hydrogenated so that there are no trans fats. Then the fatty acids from this hard oil are mixed into the fatty acids from a liquid oil. The mixed fatty acids are then reattached to the glycerol backbone into triglycerides. In this way, varying degrees of hardness can be obtained. One disadvantage is the excess of saturated fats from the fully hydrogenated oil. One advantage is the absence of trans fats.

Structured Lipids

Synthetic oils, sometimes called structured lipids, can be produced by esterification of free fatty acids to glycerol. Medium-chain fatty acids such as caprilic acid (C8:0) and capric acid (C10:0) are easily absorbed and burned similarly to carbohydrates. These medium-chain fatty acids are used in intravenous feeding and for people with problems absorbing calories. These structured lipids can be made with palmitic acid or DHA in the sn-2 position of the triglyceride for infant formulas. Absorption of fatty acids in the sn-2 position is more complete because the sn-1 and sn-3 fatty acids are stripped off during digestion. When the resulting monoglyceride is reformed into a triglyceride, the fatty acid in the sn-2 position is often retained.

DAG diacylglycerol

Oils can be produced that contain a special form of diglycerides, instead of the more common triglycerides. These oils are known by the acronym DAG (DiAcylGlycerides). These oils are designed to lower blood triglyceride levels after eating a fatty meal. In these special diglycerides, only the first and third “legs” of the triglycerides are filled with fatty acids. The center leg, sn-2, is left empty. It is healthier and safer to eat a whole-food low-fat diet, than to eat a high fat diet with synthetic oils that has been on the market for only a few years.

Fat mimetics and fat substitutes

Manufacturers want food that can be advertised as slimming, while still retaining the food appearance, flavor, and texture that is familiar. Fat mimetics are based upon modified polysaccharides or modified proteins. Fat mimetics impart stability and moisture, but cannot be heated. They are often used in low fat yogurt, cake and mayonnaise. They contain only 2 kcal per gram, rather than the 9 kcal per gram that natural fats contain.

Fat substitutes act like fat in food and can even be heated. Instead of three fatty acids on a glycerol backbone, like natural triglycerides, these often contain three fatty acids on a sucrose or sorbitol backbone. Olestra^® is one commercial example (Henry, 2009). These fat substitutes may need to be used in small amounts as excessive consumption may lead to diarrhea and the leaching of fat-soluble vitamins from the body.

Another approach is to use the glycerol backbone, but substitute structured lipids for the fatty acids. One method of manufacture is to replace the long-chain fatty acids in hydrogenated oils with short chain fatty acids such as acetic and butyric acids. These fat substitutes are only partially absorbed by the body and contain 5 kcal per gram of energy.

References:

(Carter, 1977) Carter, S.A. "The potential health hazard of substances leached from plastic packaging," J. Environ. Health, 2003, Volume: 40:2, pages: 73-76

(FAO/WHO, 1970) World Health Organization technical report series no. 462 FAO nutrition meetings report series No. 48, "Evaluation of food additives specifications for the identity and purity of food additives and their toxicological evaluation: some extraction solvents and certain other substances; and a review of the technological efficacy of some antimicrobial agents," Fourteenth Report of the Joint FAO/WHO Expert Committee on Food Additives, Geneva, 24 June-2 July, 1970. Also, Pritchard, J. L. R., Ferner, S. N. & Wong, D. R. (1964) Chem. & Ind., 2062-2065.

(Farrari, 1996) R. Ap. Ferrari, E. Schulte, W. Esteves, L. Brühl and K. D. Mukherjee, "Minor constituents of vegetable oils during industrial processing," Journal of the American Oil Chemists' Society, Volume 73, Number 5 / May,587-592 1996.

(Henry, 2009) Jeya Henry, Processing, Manufacturing, Uses and Labeling of Fats in the Food Supply, Ann Nutr Metab 2009;55:273–300.

(Hui, 2006) Y. H. Hui, Handbook of Food Science, Technology, And Engineering, CRC Press, 2006.

(OSHA, 2009) United States Department of Labor, Occupational Safety & Health Administration, "Occupational Safety and Health Guideline for n-Hexane," 2009.

Chapter 2: Three Kinds of Fat, Triglycerides, Phospholipids, and Cholesterol

Summary

This chapter will introduce you to the three major types of fatty substances: triglycerides, phospholipids, and cholesterol.

Triglycerides are the form in which fatty acids are stored for future use. Excess blood sugar and excess fats are converted in the body to triglycerides for storage. Too many triglycerides in the bloodstream raises the risk of heart disease. The carbohydrates in whole foods such as vegetables, potatoes, beans, and whole grains release slowly so the body does not make excess triglycerides. It makes sense to eat a reasonable amount of fatty food, rather than too much.

Each triglyceride has three fatty acids as its "legs." The three legs can each hold a saturated, monounsaturated, polyunsaturated, or even trans fatty acid. A triglyceride with all saturated fatty acids is more compact than one with the bent legs typical of unsaturated fatty acids. Triglycerides are digested into smaller fragments before they are absorbed.

Phospholipids are fatty substances in food and in our bodies. Soybeans are a good source. They are vitally important in the cell membrane. Phospholipids also are used to transport fats in the bloodstream.

Another well-known fatty substance is cholesterol. Cholesterol is made in the body and is not needed in the diet. We make enough cholesterol to synthesize vitamin D, male and female hormones, stress hormones, and to stiffen cell membranes.

Triglycerides in food, in fat cells, and in blood

Ninety-five percent of the fat in food is in the form of triglycerides. Also, the vast majority of fat in the human body is in the form of triglycerides. The other five percent of fatty substances is made up of phospholipids and cholesterol. Collectively, these fatty substances are called lipids. Triglycerides are a compact storage of fat. A gram of fat contains more than double the amount of energy as does a gram of either carbohydrate or protein. Fats contain 9 calories (kcal) per gram while carbohydrates and proteins have only 4 kcal per gram. The technical name for triglycerides is triacylglycerols.

Uses of triglycerides in the body

Triglycerides are important in the evolution of man and other animals. Fat allows us to have a reserve of energy. These reserves are used when we sleep. We can also rely on fat reserves during exertion. During times of famine, fat is essential to keep us alive until food becomes available. Pregnant women also have fat reserves for the needs of their growing babies.

Fat in the form of triglycerides serves as a compact storage reservoir for excess sugars in the bloodstream. Because excess blood sugar can be damaging in the blood, it is removed and stored as triglycerides. One cause of excess blood sugar is a diet high in refined carbohydrates, such as white flour products. Of course, a large intake of sugar will also raise blood sugar.

Triglycerides provide insulation from cold and they cushion internal organs. The pad on the heel of the foot is an important example of triglyceride padding. Triglycerides can serve as storage containers for essential fatty acids along with saturated and monounsaturated fatty acids. Unfortunately, triglycerides also serve as storage containers for trans fatty acids in most American diets.

Excess fat in the form of triglycerides are broken down to a two-carbon molecule called acetyl coenzyme A. Acetyl coenzyme A can then be reassembled into cholesterol and saturated fatty acids. Triglycerides are also broken down to provide glycerol. This glycerol can be changed in the liver into blood sugar when blood sugar is low.

The shape of triglycerides

The “tri” in triglycerides is included in the word because there are three fatty acids in each triglyceride. The three fatty acid “legs” are joined together with a molecule of glycerol. This glycerol backbone can be created from blood sugar inside the body. Conversely, when triglycerides are broken down for energy, this glycerol can be easily converted to blood sugar in the liver. Glycerol is made up of three groups of hydrogen and oxygen. The red atoms in the diagram below are oxygen, the white atoms are hydrogen, and the gray atoms are carbon.

Figure 7 3-D representation of a triglyceride

The character of each triglyceride can be quite different depending on the three fatty acids that form the “legs.” Each leg can be a saturated fatty acid, an essential fatty acid, a trans fatty acid, a monounsaturated fatty acid, or a polyunsaturated fatty acid.

Triglycerides are filled with fatty acids in the body with the enzyme acyl transferase. Triglycerides prefer to have a saturated fatty acid on the two outside positions and an essential fatty acid in the middle position. The first leg (called SN-1) normally has a saturated fatty acid. The middle leg normally has an unsaturated fatty acid. The third leg (called SN-3) is filled with whatever fatty acids are abundant. However, this arrangement is not possible in many fats. For instance, animal fats have very few essential fatty acids, so essential fatty acids are not available for the middle position. In flax oil, 70% of the fatty acids are essential, so most of the three legs of its triglycerides are filled with essential fatty acids.

It is interesting to note that saturated fatty acids and trans fatty acids are straight.

Figure 8 3-D representation of trans oleic acid

The figure above is a trans form of oleic acid (trans oleic acid, 18:1 n-9t).

Figure 9 3-D representation of stearic acid

Stearic acid, a saturated fatty acid is also straight as shown above (18:0).

The monounsaturated fatty acids have a single bend.

Figure 10 3-D representation of natural cis-oleic acid

The monounsaturated oleic acid looks bent as shown in the above figure (natural or cis oleic acid, 18:1 n-9c).

Polyunsaturated fatty acids have two or more bends. A triglyceride with all saturated fatty acids is more compact than one with the bent legs typical of unsaturated fatty acids.

Figure 11 A triglyceride with bent unsaturated fatty acids

Figure 12 A triglyceride with straight saturated fatty acids

Above is a triglyceride with unsaturated fatty acids. Below is a triglyceride with all saturated fatty acids. The saturated triglycerides pack together tighter and have a higher melting point.

Digestion of triglycerides

Triglycerides can be broken down in human intestines with the enzyme pancreatic lipase. This enzyme breaks the fatty acids away from the glycerol backbone. Diglycerides can be formed where only two fatty acids are left on the glycerol backbone. The "di" in diglycerides is the prefix for two. Monoglycerides can also be formed with only one fatty acid left on the glycerol backbone (mono means one). Monoglycerides normally consist of the middle fatty acid from a triglyceride and the glycerol. This is because the outer two fatty acids are the first to be removed by lipase enzymes. Triglycerides can be completely digested to form three free fatty acids and one molecule of glycerol. Triglycerides are not absorbed until they are at least partially broken down.

Health effects of excess triglycerides

Excess triglycerides in the blood are associated with higher risks for heart attacks and strokes. Levels of triglycerides over 100 milligrams per deciliter (mg/dL) and especially over 150 mg/dL can be considered to be higher than healthy. Because so many Americans have high blood triglycerides, some doctors only consider levels over 200 mg/dL of triglycerides to be unhealthy. Overeating of fatty foods, sugars, and refined carbohydrates raise blood triglyceride levels. Exercise reduces excess blood triglyceride levels. A normal healthy intake of two to three grams of the essential fatty acid alpha-linolenic acid will reduce excess blood triglyceride levels. Other sources of omega-3 fatty acids such as fish oil also reduce triglyceride levels.

The best way to control blood triglycerides is to eat the more slowly digesting complex carbohydrates so that the bloodstream is not flooded with sugars. The carbohydrates in whole foods such as vegetables, potatoes, beans, and whole grains release slowly so the body does not need to convert them into triglycerides. These complex carbohydrates can be used for energy directly. In addition to this, we all know it makes sense to eat a reasonable amount of fats, rather than too much. Children seem to know that they need to burn off extra calories after a meal. We all need daily activity and exercise to control blood triglycerides.

Phospholipids

Phospholipids are similar to triglycerides. They have a glycerol backbone, just like triglycerides. Two of the three attachment points hold fatty acids, just like triglycerides. The difference is that the third attachment point on the glycerol backbone holds a phosphate group attached to one of four different molecules.

Figure 13 Structure of triglycerides and phospholipids compared

In the diagram above we compare a triglyceride with phosphatidylcholine. Phosphatidylcholine is also known as lecithin. The third fatty acid "leg" is replaced by a phosphate group linked to choline.

Figure 14 Comparing structures of four types of phospholipids

The figure above shows the four common types of phospholipids. Phospholipids can have other molecules attached to the phosphate instead of choline. Instead of choline, the molecule attached to the phosphate can be serine, ethanolamine, or inositol.

Phospholipids are formed with a preference for certain fatty acids. One of the fatty acids is commonly a long-chain saturated fatty acid. The other fatty acid is commonly a long-chain unsaturated fatty acid. Phospholipids often store eicosanoid precursor fatty acids, such as EPA (eicosapentanoic acid) and arachidonic acid.

The phosphate group enables phospholipids to be soluble in water. On the other end, the fatty acids enable the phospholipids to be soluble in fatty substances. For example, phospholipids are used in the shell surrounding fatty substances while they are being transported in the bloodstream. The phosphate heads are compatible with the watery bloodstream while the fatty tails are embedded into the lipoprotein. Phospholipids are also used in the digestion of triglycerides. Phospholipids, mainly lecithin, are part of bile, which emulsifies fats in the intestine.

Figure 15 Phospholipids in cell membranes

One of the most important roles of phospholipids is in cell membranes. Phospholipids are embedded in and make up the cell membrane. The figure above shows how the phospholipids are placed so that the water-soluble heads are facing the outside and also the interior of the cell. The fat-soluble tails are embedded in the double membrane. The phospholipids in the cell membrane assist selective transport of molecules into and out of the cell.

Phosphatidlinositol

This phospholipid is most often found on the inside of the cell membrane, the cytosolic side. The fatty acids in phosphatidylinositol often include arachidonic acid and an 18-carbon saturated fat (stearic acid). This phospholipid can be altered to play a role in cell signaling.

Phosphatidylserine

This phospholipid is found on the inside of the cell membrane. While cells are healthy, it is kept on the inner side of the cell membrane. Normally, phosphatidylserine is kept on the inner membrane by an enzyme called flippase. Just before programmed cell death (apoptosis), the phosphatidylserine can migrate to the outer membrane. This migration to the outer membrane may be a sign of dementia or Alzheimer's disease. Half of the total body content of this phospholipid is found in the brain where it makes up about 15% of the phospholipids.

Phosphatidylserine in the inner cell membrane can alter membrane fluidity. It also interacts with membrane proteins to modulate the activity of receptors and signaling molecules (Jager, 2007).

Phosphatidylcholine

Phosphatidylcholine Is found in high amounts in egg yolks and soybeans. This phospholipid is a major component of the outer cell membrane. Phosphatidylcholine plays a role in membrane mediated cell signaling.

The major neurotransmitter of nerves that stimulate muscles is acetylcholine. Acetylcholine is synthesized from choline. Choline is not now deemed an essential nutrient, but more choline may be needed at times than can be synthesized in the body. This is especially true during heavy exercise. Dietary phosphatidylcholine can supply extra choline when it is needed.

Phosphatidylethanolamine

Phosphatidylethanolamine is also known as cephalin. It is found in cell membranes. Content of phosphatidylethanolamine is highest in the white matter of the brain, in nerves, and in the spinal cord. While phosphatidylcholine is the principal phospholipid in animals, phosphatidylethanolamine is the principal one in bacteria.

Sphingolipids

The best known sphingolipid is sphingomyelin, which protects nerve cells. Sphingolipids are a different type of phospholipid because they use sphingosine instead of glycerol as a backbone. Sphingolipids are similar to other phospholipids in that they may contain ethanolamine, serine, or choline. They contain just one fatty acid, normally of 18 or 20 carbon atoms in length. Sphingolipids play important roles in signal transmission and cell recognition.

Sphingolipids such as myelin are believed to protect the cell membrane against harmful environmental factors by forming a stable and chemically resistant outer cell membrane.

Glycosphingolipids are a type of sphingolipids that may be involved in cell recognition and signaling.

Figure 16 The structure of sphingomyelin, a type of sphingolipid

Sphingomyelin is a type of sphingolipid found in cell membranes, especially in the myelin sheath that surrounds some nerve cell axons. It can contain either choline or ethanolamine. It represents about 85% of our sphingolipids.

Cholesterol and other sterols

Cholesterol is a fatty substance, although it is quite different from other fatty substances such as triglycerides and phospholipids. Cholesterol is synthesized in the body and dietary cholesterol is not required. The average person synthesizes about one gram of cholesterol each day. About one-quarter of the synthesis takes place in the liver. Cholesterol is also synthesized in the adrenal glands and other glands where steroid hormones are made. Statin drugs inhibit an enzyme necessary for the creation of cholesterol in the liver. Statin drugs also inhibit the synthesis of ubiquinone (coenzyme Q10) by an average of 40% (Ghirlanda, 1993). Coenzyme Q10 is necessary for energy production and is an important antioxidant. It is healthier to adjust the dietary causes of excess blood cholesterol than to limit cholesterol synthesis with drugs.

Cholesterol is the raw material for synthesizing steroid hormones such as cortisol (a stress hormone) and testosterone. Cholesterol is also the starting point for the synthesis of the active form of vitamin D. Cholesterol is used in all cell membranes to control stiffness and fluidity. Cholesterol is also found in bile acids.

Figure 17 The structure of cholesterol

Figure 18 The structure of stigmasterol

Cholesterol in the bloodstream is famous for its link to the risk of heart attacks. Cholesterol is transported in the bloodstream in lipoproteins. LDL (low density lipoproteins) are considered "bad" cholesterol transporters when in excess. Excess, oxidized cholesterol can be taken up by immune system cells called macrophages. The macrophages can become engorged and form foam cells. The foam cells can be trapped in the walls of arteries. Over the course of decades, the arteries can become partially blocked, narrowed, and stiffened. This is the progression of atherosclerosis, which can lead to heart attacks and strokes. This progression can be regulated by diet. Lower dietary intakes of total fat, saturated fat, and excess calories may reduce or reverse the progression of atherosclerosis. Higher dietary intakes of antioxidants, especially vitamin E and vitamin C, reduce the progression of atherosclerosis. Both of these dietary objectives are met with a whole food, plant-based, low-fat diet.

Plant sterols

Plant sterols are called phytosterols. Important phytosterols include stigmasterol, campesterol, sitosterol, and Brassicasterol. The planet sterols cannot perform the same functions as cholesterol. Nevertheless, their structures are remarkably similar. A figure of stigmasterol is shown above near the cholesterol figure showing their similarities.

Plant sterols in the diet, especially sitosterol, can block some of the absorption of cholesterol, thus reducing blood cholesterol levels. Ergosterol is found in the cell membranes of fungi and plays a role similar to cholesterol in human cell membranes.

References:

(Ghirlanda, 1993) Ghirlanda G, Oradei A, Manto A, Lippa S, Uccioli L, Caputo S, Greco AV, Littarru GP, "Evidence of plasma CoQ10-lowering effect by HMG-CoA reductase inhibitors: a double-blind, placebo-controlled study," J Clin Pharmacol. 1993 Mar;33(3):226-9.

(Jager, 2007) Ralf Jäger, Martin Purpura, and Michael Kingsley, "Phospholipids and sports performance," Journal of the International Society of Sports Nutrition, 2007, 4:5.

Chapter 3: Digestion and Transport of Food Fats

Summary

Fats and oils are digested and absorbed in the intestine with almost 100% efficiency. Bile from the gallbladder emulsifies the fats. The emulsified fats are split up with pancreatic enzymes. Most fats and oils are made up of triglycerides. These triglycerides are broken up before absorption. After absorption, the smaller fatty acids are sent to the liver in blood vessels. The larger fatty acids are reassembled into triglycerides and packaged into chylomicrons. The chylomicrons are sent through the lymph system into the bloodstream. Chylomicrons also contain small amounts of cholesterol and phospholipids.

Transport of fats in the bloodstream is accomplished with lipoproteins. The liver packages dietary and internally-made fats and cholesterol into very low density lipoproteins. These circulate and distribute triglycerides to muscle cells and fat cells. Vitamin E is crucial to protect the arteries from oxidized fats. As the very low density lipoproteins lose their triglycerides, they become low density lipoproteins—the well known "bad" cholesterol LDL. If there is an excess of dietary saturated fats, LDL levels are higher and constitute a major risk factor for clogged arteries, heart attacks, and strokes. HDL (high density lipoproteins) are considered beneficial because HDL takes cholesterol to the liver for removal.

Saturated fats and trans fats are burned for energy. Essential fatty acids that are not needed for eicosanoid production are also burned for energy. Fats are burned in the energy factories of the cell, the mitochondria. The fatty acid chains are broken into two-carbon fragments and burned to create energy.

Digestion of fats and oils

Our digestive system processes fats, oils, cholesterol, and phospholipids every day. Collectively, these fat-soluble nutrients are called lipids. Absorption of lipids is high and is often 95% efficient. Lipids are fat-soluble, but our digestive juices are water based. Our digestive enzymes for fat-soluble nutrients are called lipases. Lipases are water-soluble enzymes that break apart fatty substances. The name lipase comes from lipid and -ase (the suffix for enzymes).

Figure 19 Triglyceride structure, black is carbon, white is hydrogen, and red is oxygen

The vast majority of fatty substances (about 95%) are triglycerides. Triglycerides consist of three fatty acids attached to a glycerol backbone, as shown above. Triglycerides cannot be absorbed intact. They need to be at least partially dismantled to be absorbed.

Digestion of fats in the mouth and stomach

Adults do not digest fats or oils in the mouth or stomach to any appreciable extent. In the mouth, some fats are melted. Many of the saturated and trans fatty acids have too high a melting point to melt at body temperatures. Cholesterol melts at 300 degrees Fahrenheit (140 C), well above body temperature. In infants, an enzyme called lingual lipase ("tongue fat enzyme") breaks apart short and medium chain fatty acids. Lingual lipase is released by a gland under the tongue of infants.

In the stomach, churning action breaks apart fatty food. Gastric lipase ("stomach fat enzyme") is secreted, but plays a very small role in fat digestion. Gastric lipase is only able to act upon some of the short and medium chain fatty acids.

Bile emulsifies fat

Almost all lipid digestion takes place in the small intestine. To prepare for the digestion of fats, the liver produces bile, which contains cholesterol. Bile is stored in the gall bladder until needed. When fats are detected in the small intestine, a hormone called cholecystokinin is released. Cholecystokinin triggers the release of bile from the gallbladder.

Bile consists of bile salts, bile acids, cholesterol, phospholipids, antibodies, electrolytes, water, and bilirubin. Bile acids are made from cholesterol with amino acids attached. The attached amino acids help bile to form micelles, tiny balls of emulsified fat. The main phospholipid in bile is lecithin, an emulsifier. Bile salts are mainly formed with sodium, but sometimes with potassium or calcium. Bilirubin is a yellow bile salt formed from hemoglobin.

Figure 20 Bitter tonics can stimulate bile after fatty meals

Text Box: Bitter tonics can stimulate bile after fatty meals
Dandelion root (Taraxacum Officinale) and Gentian (Gentiana Lutea) are used after meals high in fat to encourage bile production and relieve that "full" feeling.

Bile acts like a clothes detergent to break up greasy substances. Bile helps break up large globules of fat into smaller globules. Fats and oils want to float on watery fluids, but bile helps to get these lipids to mix in with the watery digestive fluids. The small particles of emulsified fat repel each other and mix in with the digestive fluid. This allows digestive enzymes access to break apart the fat.

The smaller the size of the food pieces, the more access the digestive enzymes have to break them apart. With nuts and seeds, it is important to chew them well to promote complete digestion. Grinding or blending nuts and seeds produces smaller pieces than chewing. These smaller pieces can be more thoroughly digested. It is also helpful to grind up other fatty food choices either with teeth or mechanically.

Figure 21 How hydrolysis splits two fatty acids off of a triglyceride

Digestion of fats and oils in the intestine

There is a only small role played by intestinal lipases. The main digestive enzymes for fat digestion are pancreatic lipases. Pancreatic lipases are able to remove fatty acids from triglycerides in a process called hydrolysis (shown above). Hydro- refers to the water molecules that are added and -lysis means "to split up."

Pancreatic lipases work first on the outer fatty acids. The outer two fatty acids are removed first, leaving a monoglyceride. A monoglyceride has just one fatty acid left on the glycerol backbone, as shown in red above. Sometimes all three fatty acids are removed, leaving three free fatty acids and glycerol. Sometimes only one fatty acid is removed, leaving the glycerol backbone with two fatty acids attached. This is called a diglyceride. Triglycerides cannot be absorbed intact and diglycerides have limited absorption.

Phospholipids have two fatty acids attached. The process of digestion is similar to triglycerides. The two fatty acids are removed by pancreatic lipase, leaving a phospholipid fragment. Once broken up, the parts of the phospholipid are absorbed.

Cholesterol can be absorbed intact. If there are any side chains of fatty acids, they are first removed with lipase enzymes. Cholesterol can be oxidized during cooking. This oxidized cholesterol, sometimes called oxysterol, can increase the risk of heart disease by damaging arteries (Lukyanenko, 2009).

Most of the bile released from the gallbladder is reabsorbed. Some bile becomes bound to dietary fiber and is excreted. The excretion of bile effectively lowers blood cholesterol. The best types of fiber for removing excess cholesterol in bile are the soluble pectins and gums found in fruit, oats, and beans.

Absorption of lipids

There are two distinct routes for absorption of lipids from the intestine. The smallest lipid particles can go into the portal blood system and be transported to the liver. Larger lipid fragments are reprocessed and sent to the bloodstream via the lymph system.

The small lipid particles in the intestine include glycerol and short and medium length fatty acids. These small particles can diffuse easily into the intestinal cells. They are absorbed directly into the portal blood system. The portal blood system is not connected to the general bloodstream. The portal system takes nutrients from the digestive system and transports them to the liver, where they may be processed further.

Micelles

Monoglycerides and the long-chain fatty acids require some processing before being absorbed. While still inside the intestine, these larger fragments of lipids are collected into micelles. Micelles are tiny droplets of bile surrounding fatty acids and monoglycerides. Micelles are soluble in the watery intestinal fluid and are easily transported to the intestinal cells (enterocytes). Other lipids are also included in micelles. Phospholipid fragments, cholesterol, and the fat-soluble vitamins are collected into micelles. The monoglycerides, fatty acids, and other lipids in micelles are able to diffuse into the intestinal cells from the digestive tract.

Chylomicrons

Once the long-chain fatty acids (14 to 22 carbon atoms long) and glycerol have diffused into the intestinal cells, they are reassembled into triglycerides. Inside the intestinal cells, triglycerides, cholesterol, phospholipids, and fat-soluble vitamins are assembled into chylomicrons. Chylomicrons are spherical balls with an outer layer of phospholipids. The phospholipid heads are soluble in the watery environment of the lymph stream and bloodstream, while the phospholipid tails are compatible with the fatty contents of the chylomicrons. Also on the exterior of the chylomicrons are special proteins that identify the chylomicrons. Initially, chylomicrons have the signaling protein apolipoprotein B-48 embedded in their surface.

Inside the new chylomicrons, the main lipids are triglycerides. Triglycerides make up 85% of the lipids in freshly made chylomicrons. Chylomicrons also contain a small amount of cholesterol, cholesteryl esters, phospholipid fragments, and fat-soluble vitamins.

Once assembled, the chylomicrons are secreted into tiny lymph ducts called lacteals. The lacteals lead into larger lymph ducts. The chylomicrons are secreted into the thoracic duct, which is the largest lymph vessel in the body. The chylomicrons then enter the bloodstream at the left subclavian vein near the heart. These lipids do not initially go through the liver. If vitamin E is not available during the assembly of these chylomicrons, oxidative damage to the artery walls is possible. Oxidative damage to artery walls is a major factor in atherosclerosis and heart disease (Nakamura, 2006).

Lipoproteins: transport of lipids through the bloodstream

Lipoproteins enable transport of lipids through the watery medium of the bloodstream. There are four main lipoproteins: chylomicrons, very low density lipoproteins (VLDL), low density lipoproteins (LDL), and high density lipoproteins (HDL). All of these lipoproteins have outer shells made with phospholipids. The phospholipid heads are water friendly and form the outer shell of these lipoproteins. The phospholipid tails are lipid friendly and are contained in the inside of these phospholipids. Embedded in the outer shell are signaling proteins that identify the lipoprotein. These proteins are called apolipoproteins.

Chylomicron transport

Chylomicrons are the only lipoprotein that directly transports dietary fats. They are the least dense and the largest of the lipoproteins. Chylomicrons acquire a signaling protein that stimulates lipoprotein lipase activity. This signaling protein is called apolipoprotein C2. Lipoprotein lipase is an enzyme used by cells to extract lipids from lipoproteins. As chylomicrons pass through the body, cells, primarily muscle and fat cells, remove triglycerides and other lipids from them using the enzyme lipoprotein lipase. The chylomicrons get smaller and smaller. They are almost totally absorbed after 14 hours. The remnants of the chylomicrons are recovered by the liver and used to build other lipoproteins.

Very low density lipoproteins

Liver cells take in various lipids arriving in the general bloodstream and from the portal blood system. Liver cells also synthesize cholesterol and saturated fatty acids. Palmitic acid (16:0) is the main saturated fat synthesized. The liver cannot synthesize saturated fatty acids shorter than palmitic acid. Palmitic acid can be lengthened to stearic acid (18:0). Both saturated fats and cholesterol can be synthesized from two-carbon fragments. These two-carbon fragments can be made from fatty acids, carbohydrates, alcohol, or even protein.

The lipids made in the liver, along with lipids collected by the liver, are packaged into very-low-density lipoproteins (VLDL). These are spherical globules coated with phospholipids and embedded with signaling proteins. Inside VLDL are cholesterol, phospholipid fragments, and triglycerides. The mix of lipids inside VLDL varies with the lipids available to the liver. Sometimes the lipids inside VLDL are made up of 10% cholesterol and 90% triglycerides. At other times, VLDL may start out containing about 15% cholesterol. In all cases, most of the lipids inside VLDL are triglycerides.

Vitamin E and lipoproteins

Before being released from the liver, the VLDL are protected with alpha-tocopherol, a form of vitamin E. The liver loads each VLDL up with vitamin E. If vitamin E is not available, the VLDL will not be protected from oxidation. VLDL unprotected by vitamin E can damage the inside of the arteries, potentially worsening atherosclerosis.

Unfortunately, most of the vitamin E used for supplementation is synthetic and made up of isomers that are ineffective in protecting VLDL and our arteries. There are eight isomers of alpha-tocopherol in synthetic vitamin E; four of them are ineffective, and three of the others are less effective as antioxidants (Blake, 2008). Synthetic vitamin E is called "all-racemic" in medical literature and called "dl-alpha-tocopherol" on vitamin labels.

VLDL becomes LDL

VLDL starts out about half the size of a new chylomicron. As VLDL circulates in the bloodstream, it supplies triglycerides and other lipids to cells along the way. The enzyme lipoprotein lipase in muscle and fat cells removes lipids from the VLDL. As the VLDL loses triglycerides, it shrinks. The composition of VLDL also changes as it circulates. As it loses triglycerides, VLDL goes through a stage where it is known as intermediate-density lipoprotein. When the cholesterol content becomes higher than the triglyceride content, it is named low-density lipoprotein (LDL).

Figure 22 How VLDL becomes LDL, with changes in cholesterol and triglycerides

LDL: Low density lipoproteins

The exact composition of LDL is constantly changing. LDL is made up of at least half cholesterol. As LDL passes through the bloodstream, triglycerides wind up making up less than 10% of the contents of the LDL. It is interesting that LDL, including the outer shell, can also be made up of 20% phospholipids. Each LDL has a single molecule of a signaling protein called apolipoprotein B-100. LDL is much smaller than VLDL, perhaps one-quarter the size.

LDL is known as "bad" cholesterol because too much of it in the bloodstream can increase atherosclerosis. LDL is also necessary to supply cholesterol for building cell membranes and as a raw material for hormones and vitamin D. When a cell requires cholesterol, it synthesizes the necessary LDL receptors, and inserts them into the outer leaf of its cell membrane.

The LDL content of blood is carefully regulated by LDL receptors on liver cells and other cells. The liver will remove excess cholesterol. Unfortunately, excess dietary saturated fatty acids not only lead to extra cholesterol production by the liver, but they also suppress expression of LDL receptors on liver cells (see chapter 4). It is healthiest to keep saturated fatty acid intake to 7% or less of daily calories. This is best accomplished with a plant-based diet. Trans fatty acids also suppress LDL receptor activity.

High density lipoproteins

Our liver makes another type of lipoprotein called high-density lipoproteins (HDL). HDL are designed to scavenge extra lipids from the bloodstream and return them to the liver for disposal. HDL are called "good" cholesterol because they are needed to remove the excess cholesterol so common in the blood of people who eat too much saturated fat. HDL remove excess cholesterol, free fatty acids, phospholipids, and glycerol from circulation. HDL have signaling proteins on their outer surfaces that tell the liver to dispose of or recycle the lipids inside.

There is only one kind of cholesterol. HDL and LDL are transport containers with different proportions of cholesterol and triglycerides. Dietary cholesterol is always undesirable and never necessary. Adequate cholesterol is made in the body. It is estimated that the liver makes 50,000,000,000,000,000 molecules of cholesterol per second. Excessive dietary cholesterol can elevate blood cholesterol levels, but excess saturated fats more powerfully boost blood cholesterol. Dietary sources of cholesterol and saturated fats include meat, chicken, fish, dairy products, and eggs. Cholesterol is not found in food from plant sources. Outside of palm products, such as coconut meat, plant products are low in saturated fats.

Figure 23 Healthiest ratios between total cholesterol and HDL

Text Box: The ratio of total cholesterol to HDL: the smaller the number the better.
With a high cholesterol level of 240 mg/dL and a HDL of 60 mg/dL the ratio is 4
With a high cholesterol level of 240 mg/dL and a HDL of 35 mg/dL, the ratio is 6.9
With a low cholesterol level of 150 mg/dL and a HDL of 60 mg/dL the ratio is 2.5

Reports from the Framingham Heart Study suggest:
For men, a total cholesterol-to-HDL ratio of 5 signifies average risk for heart disease; 3.4, about half the average risk; and 9.6, about double the average risk.
For women, who tend to have higher HDL levels, a ratio of 4.4 signifies average risk; 3.3 is about half the average; and 7, about double the average risk.

Measuring blood LDL and HDL levels

LDL blood levels are measured to determine the level of risk of heart attacks and strokes. The American Heart Association has declared levels below 100 mg/dL optimal. 100-129 mg/dL is considered almost optimal. 130-159 mg/dL is considered borderline high and 160-189 is considered high. Over 190 mg/dL is considered too high. Remember that to become “heart attack proof” LDL needs to be below 70 mg/dL.

HDL blood levels should be 60 mg/dL or higher to provide protection from heart disease, according to the American Heart Association in 2009. People with HDL levels below 40 mg/dL are considered to be at higher risk.

Measuring total serum cholesterol

Measurements of total cholesterol are also used to gauge the risk of heart disease. Total cholesterol is the sum of all cholesterol in blood, including cholesterol inside LDL and HDL. Because the amount of HDL is small compared to LDL, risk levels indicated by total cholesterol are similar to risk levels indicated by LDL. Keeping total serum cholesterol levels below 150 mg/dL keeps risks of heart disease low. Keeping cholesterol below 150 mg/dL lowers risk of ishemic heart disease to near zero (Esselstyn, 1999). Many doctors and the American Heart Association recommend that total cholesterol be kept lower than 200 mg/dL. However, it is important to note that 35% of heart attacks in the Framingham study happened to people with total cholesterol between 150 mg/dL and 200 mg/dL (Castelli, 1996). Over 100 million Americans have total blood cholesterol over 200 mg/dL.

Ratios of lipoproteins

There are several different ratios of lipoproteins to gauge the risk of coronary heart disease. The best indicator may be the ratio of total cholesterol to HDL (Ingelsson, 2007). The ratio of serum LDL to serum HDL is also used to gauge the risk of atherosclerosis and heart disease. Another very accurate measure of heart disease risks is the ratio of apolipoprotein B to apolipoprotein A-I. However, the public and doctors are better acquainted with total cholesterol levels and HDL levels. Standards are harder to find for the ratio between apolipoproteins and testing is not as available.

Metabolism of fats and oils

Fatty acids in triglycerides are used for insulation, for padding, and stored for future energy. In this section we will look at how fatty acids are burned for energy, or metabolized. Once the fatty acids are absorbed, they are reassembled into triglycerides. The triglycerides are delivered to the cells in chylomicrons and lipoproteins. Cells then can take in the fatty acids for storage or for energy.

Fatty acids inside cells can be broken down to produce energy. The fatty acids are first broken into two-carbon fragments. The process to produce these two-carbon fragments is called beta-oxidation. Step by step the fatty acids, many of which are 18 carbon atoms, release two carbon atoms at a time.

Figure 24 Involvement of B-vitamins in the metabolic burning of fat

The two-carbon fragments are combined with coenzyme A (CoA). It is interesting to note that a large part of coenzyme A is made up of the B-vitamin pantothenic acid. Together the two-carbon fragments and coenzyme A are called acetyl-coenzyme A (acetyl-CoA). Acetyl-coenzyme A is the raw material for the aerobic energy cycle of the cell. The aerobic energy cycle of the cell is now called the tricarboxylic acid cycle (TCA cycle); it used to be called the Kreb's cycle. As you can see from the above figure, acetyl-CoA is the starting point for energy production.

Several B vitamins are used in the conversion of fatty acids to acetyl-CoA. Riboflavin (vitamin B₂), niacin (vitamin B₃), biotin, and vitamin B₁₂ are all involved in conversion between fatty acids and acetyl-CoA.

Once the fatty acids are converted into acetyl-CoA, they can go through the energy cycle to produce high-energy phosphates. This energy cycle takes place in the mitochondria, tiny organelles inside the cell. Adenosine triphosphate (ATP) is a high-energy phosphate used to power muscle contraction and other energy needs.

The aerobic energy cycle burns fat very efficiently. Besides energy, it produces water and carbon dioxide.

References:

(Blake, 2008) Blake, Steve, "Vitamins and Minerals Demystified," 2008 McGraw-Hill, New York, pages 121-122.

(Castelli, 1996) Castelli W. From the desk of William P. Castelli, Medical Director, Framingham Cardiovascular Institute, Framingham. MA. Prevention 1996;48:61-64.

(Esselstyn, 1999) Esselstyn CB Jr., "Updating a 12-year experience with arrest and reversal therapy for coronary heart disease (an overdue requiem for palliative cardiology)," Am J Cardiol. 1999 Aug 1;84(3):339-41, A8.

(Ingelsson, 2007) Erik Ingelsson, Ernst J. Schaefer, John H. Contois, Judith R. McNamara, Lisa Sullivan, Michelle J. Keyes, Michael J. Pencina, Christopher Schoonmaker, Peter W. F. Wilson, Ralph B. D’Agostino, and Ramachandran S. Vasan, "Clinical Utility of Different Lipid Measures for Prediction of Coronary Heart Disease in Men and Women," JAMA, Vol. 298 No. 7, August 15, 2007.

(Lukyanenko, 2009) Valeriy Lukyanenko‌ & Yevgeniya Lukyanenko, "Oxysterols in heart failure," Future Cardiology, July 2009, Vol. 5, No. 4, Pages 343-354.

(Nakamura, 2006) Y. Nakamura, M. Read, J. Elias, S. Omaye, "Oxidation of serum low-density lipoprotein (LDL) and antioxidant status in young and elderly humans," Archives of Gerontology and Geriatrics, 2006, Volume 42, Issue 3, Pages 265-276.

Part II: Four Kinds of Fat

Chapter 4: Saturated fats, the hard fats

There are only three basic types of fatty acids: saturated, monounsaturated, and polyunsaturated. Trans fatty acids are variants of either monounsaturated or polyunsaturated fatty acids. This chapter will help you to get to know the saturated fatty acids.

Summary

Saturated fats are used in the body as fuel for muscles and for energy storage. They also are needed in cell membranes to adjust the cell membrane stiffness. We do not have any requirement for dietary saturated fats. We make all that we need inside our bodies. Excess fats and sugars in the bloodstream are automatically converted to saturated fats and stored in the body. Saturated fats are found in virtually all fat-containing food in varying amounts.

When excesses of saturated fats are consumed, this raises blood cholesterol. Elevated blood cholesterol, over time, causes clogging of the arteries. Excesses of saturated fats are the principal cause of heart attacks and strokes. A whole food diet based upon plant foods low in saturated fat is the healthiest diet for preventing heart attacks. As more saturated fat is introduced into the diet, heart attack risks are raised.

The most dangerous foods that raise blood cholesterol are cheese, butter, and other fatty dairy products. Coconut meat is also particularly high in artery-clogging saturated fats. Meat, chicken, and eggs have high amounts of saturated fats. But plants can contain saturated fats too; consuming large amounts of avocados, Brazil nuts, olive oil, and cottonseed oil can raise blood cholesterol levels. Fish has moderate to low amounts of saturated fats.

The structure of all saturated fatty acids is remarkably similar. Each saturated fatty acid consists of a chain of carbon atoms. Common lengths of carbon chains in saturated fats are 12 to 18 carbon atoms long. They are called fatty "acids" because one end of the carbon chain is a mild acid. This is the end that is normally attached to triglycerides. Although all saturated fatty acids are structurally similar, only three of them are known to contribute to elevated blood cholesterol and heart disease: lauric acid, myristic acid, and palmitic acid. Of these three, palmitic acid is found in the highest amounts in American diets, commonly in livestock products.

Uses of saturated fats in our bodies

Saturated fatty acids are used inside our bodies principally as fuel. The short and medium length saturated fatty acids are easiest to digest and burn. Compared to the long-chain saturated fatty acids, the short and medium length saturated fatty acids are absorbed and transported more like carbohydrates.

Saturated fatty acids are also used in the cell membranes. In the cell membranes the longer saturated fatty acids stiffen the membranes and prevent excess fluidity. The saturated fatty acids attached to phospholipids in cell membranes also physically separate the polyunsaturated fatty acids.

Figure 25 How Excess Saturated Fats Raise Blood Cholesterol

Text Box: How Excess Saturated Fats Raise Blood Cholesterol

LDL circulates in the blood stream for longer periods of time.
There are a reduced number of LDL receptors on the cell membranes.
They reduce the amount of cholesterol cleared by bile.

The longer LDL is circulating in the bloodstream, the more likely that it will become oxidized.
This results in more damage to the inside of the arteries, thus contributing to atherosclerosis.

How excess saturated fats increase blood cholesterol

The correct amount of saturated fatty acids in cell membranes is necessary for good health. Excesses of saturated fatty acids in cell membranes reduce the ability of the cells to remove fats and cholesterol from the bloodstream. Dietary saturated fatty acids also increase the synthesis of fatty acids. How do dietary saturated fats increase blood cholesterol content?

Excess dietary saturated fatty acids result in more LDL (low density lipoprotein) circulating in the bloodstream for longer periods of time. Compared to polyunsaturated fats, saturated fats increase the secretion of VLDL (very low density lipoproteins). This also leads to higher levels of LDL.

Higher saturated fat levels also have been shown to increase the persistence of VLDL and LDL in the bloodstream. The longer the LDL is circulating in the bloodstream, the more likely it is that it will become oxidized. This results in more damage to the inside of the arteries, thus contributing to atherosclerosis.

Excess dietary saturated fatty acids reduce the number of valuable LDL receptors on the cell membranes (Fernandez, 2005). These LDL receptors are vital for removing cholesterol from the bloodstream, especially by liver cells. Dietary polyunsaturated fatty acids, as compared to saturated fatty acids, double the amount of LDL removed from the bloodstream.

Excess dietary saturated fatty acids also reduce the amount of cholesterol cleared by bile (Fernandez, 2005).

Saturated fats and disease

Saturated fats have no known role in preventing disease. Quite the opposite, hundreds of studies have shown that higher dietary saturated fat intake leads to higher total blood cholesterol and a higher risk of heart attacks (FNB, 2005). Reducing saturated fats in the diet, or replacing them with healthier polyunsaturated fatty acids greatly reduces heart attacks. Replacing 5% of saturated fats with unsaturated fats was reported to result in a remarkable 42% decrease in coronary heart disease (Hu, 1999) .

Saturated fats and diabetes

Several large epidemiological studies have shown an increased risk of diabetes coinciding with an increased intake of saturated fatty acids. This is because higher levels of dietary saturated fats have been found to reduce glucose tolerance and insulin sensitivity. The excess saturated fatty acids in the cell membranes make it more difficult for the cells to take in blood sugar. This is exactly the problem in type II diabetes. Reducing saturated fat intake by just 6% was associated with a beneficial 25 percent decrease in insulin concentrations after a meal (FNB, 2005).

Saturated fats and blood cholesterol

Some of the saturated fatty acids are known to raise blood cholesterol when included in a diet. Elevated blood cholesterol is a major risk factor for heart attacks, angina, and strokes. Of all of the saturated fatty acids, only lauric acid, myristic acid, and palmitic acid are known to raise blood cholesterol. Stearic acid, another saturated fatty acid, is converted to oleic acid inside our bodies and so is not known to raise blood cholesterol. Stearic acid has, however, been found to lower the "good" HDL cholesterol. Stearic acid, lauric acid, myristic acid, and palmitic acid have been found to raise blood triglycerides after a meal, increasing risks of heart disease.

The three saturated fatty acids that raise blood cholesterol are palmitic acid, myristic acid, and lauric acid. Beef, cheese, and hamburgers have been found to be the major contributors of palmitic acid in typical diets in developed countries. Dairy products are the major contributors of myristic acid to diets in the developed world. Coconut oil and palm kernel oil are major contributors of lauric acid in people who consume these palm products.

It is not possible to eliminate all saturated fatty acids from a diet because there are some saturated fatty acids even in vegetable oils. However, since humans have no need to eat any saturated fatty acids, the lowest amount of dietary saturated fatty acids possible is the healthiest amount.

How much saturated fat is too much?

The American Heart Association recommends an upper limit of 7% of calories from saturated fatty acids. This works out to only about one tablespoon of saturated fatty acids per day.

Here is how to figure out how many grams of saturated fatty acids we should eat in a day. In a 2200 calorie (kcal) diet, 7% of calories comes out to 154 calories. Since fat has 9 calories per gram, 154 calories is equal to about

17 grams of saturated fatty acids. Seventeen grams of most fats is about one tablespoon.

Remember that even "saturated foods" such as lard and butter contain only about half of their fatty acids as saturated fats. So the American Heart Association recommendation means limiting fats from animal products to about two tablespoons daily. Because coconut oil and palm kernel oil are about 75% or more saturated, these should be limited to 1 1/2 tablespoons per day.

A lengthy report by the World Health Organization in conjunction with the Food and Agriculture Organization (WHO, 1993), Fats and oils in human nutrition: Report of a joint expert consultation, recommends 10% of calories as an upper limit for saturated fats. This works out to 24 grams of saturated fatty acid daily on a 2200 calorie (kcal) diet.

The Institute of Medicine, the health arm of the National Academy of Sciences, has reported that, "In general, the higher the intake of saturated fatty acids, the higher the serum total and low density lipoprotein (LDL) [bad] cholesterol concentrations." They further state, "There is a positive linear trend between total saturated fatty acid intake and total and LDL cholesterol concentration and increased risk of CHD [coronary heart disease]. A UL [upper limit] is not set for saturated fatty acids because any incremental increase in saturated fatty acid intake increases CHD risk (FNB, 2005)." The Institute of Medicine could not set an upper limit for saturated fats because they found that less is better, but zero is unattainable.

A healthful goal for saturated fat is 12 grams daily, rather than the 17 grams that the American Heart Association recommends, or the 24 grams that the WHO/FAO recommends. This works out to about 5% of calories on a 2200 calorie (kcal) diet. This more conservative goal of 12 grams per day of saturated fatty acids would greatly reduce deaths from heart attacks. It would also greatly reduce the agony of angina and the misery of strokes. It is attainable with a satisfying healthful diet.

Saturated fats made in the body

When excess fats or carbohydrates are eaten, they are made into saturated fatty acids and cholesterol. The fats or carbohydrates are broken down to 2-carbon fragments called acetyl coenzyme A. When there are excesses of acetyl coenzyme A, the excesses are built up into palmitic acid. Palmitic acid is the most common saturated fatty acid in the human body. Cholesterol is also built up from two-carbon fragments.

The 16-carbon palmitic acid is the shortest saturated fatty acid that humans can synthesize. It can be lengthened with an elongase enzyme to become the 18-carbon saturated fatty acid stearic acid. Then, if a monounsaturated fat is needed, we have another enzyme that can convert stearic acid to oleic acid. The only difference between stearic acid and oleic acid is that oleic acid has a double bond positioned 9 carbon atoms from the omega end. The enzyme delta-9 desaturase can insert this double bond to convert stearic acid to oleic acid.

Saturated fats in food

It is clear that we must limit the amount of saturated fats in our diets. To do this we must know which foods to limit. Consider the following graph:

Figure 26 The saturated fatty acid content of one serving of various foods

The graph above shows the saturated fatty acid content of one serving of various foods. It is not surprising that cheese, meat, and eggs are high in saturated fat. It is surprising that avocado and peanut butter have a significant content of saturated fatty acids. Now, let us consider the saturated fat content of nuts and seeds.

Figure 27 The amount and variation of saturated fats in some common nuts and seeds

The graph on the left above shows the amount and variation of saturated fats in some common nuts and seeds. The graph on the right above shows just the atherogenic saturated fatty acids. The atherogenic fatty acids are the ones proven to raise blood cholesterol: palmitic, myristic, and lauric acids. You may note that macadamia nuts and cashews both look better when considering just the atherogenic saturated fatty acids.

In the above graphs, I am comparing the amount in one serving with a conservative daily maximum of 12 g. Remember that the American Heart Association sets a limit of 17 g per day. With most of the nuts and seeds, it would take 4 or more servings to start approaching the amount of saturated fats that are tolerable in a day. Coconuts are one notable exception with only one serving per day supplying nearly the daily maximum of saturated fats. We think of only animal fats as having abundant amounts of saturated fats, yet we must be careful with coconut, macadamia nuts, and Brazil nuts as well. Now let us take a look at the saturated fat content of livestock products.

Figure 28 A comparative graph of saturated fats in common livestock products

Above is a comparative graph of saturated fats in one serving of various common livestock products. As you can see, cheese is very high in saturated fats. Hamburger, bologna, Spam, whole milk, and butter are high in saturated fats. One serving of these livestock products contains a maximum amount of saturated fats for an entire day. It is interesting to note that skim milk and wild deer meat are very low in saturated fats. The cholesterol content is included because dietary cholesterol also contributes to blood cholesterol, albeit in a minor way compared to saturated fats. Now we can take a look at the saturated fat content of common fats and oils.

Figure 29 The amount of saturated fats in two tablespoons of common fats and oils

In the graph above, the amount of saturated fatty acids in two tablespoons (about 28 g) of common fats and oils is shown. The amount of saturated fats does not differ too much from the amount of the atherogenic (artery-clogging) saturated fats. One notable exception is cocoa butter, which has 60% saturated fats, but only 25% of the atherogenic saturated fats. Cottonseed oil has a high content of saturated fatty acids compared to most other vegetable oils.

Saturated fats in diets

Most of the scientific literature on fats discusses fatty acids without looking at the amounts in common food. Looking at food and its saturated fatty acid content is interesting. Perhaps more important and revealing is to look at the saturated fatty acids in different diets. This section will look at the saturated fatty acid content of one day's diet for some well-known diets. We will start with an analysis of a common example of the Atkin's diet.

Figure 30 Graph of saturated fat in an Atkin's diet

The 50 grams of saturated fat in this Atkin's diet far exceeds guidelines of 12, 17, or 24 grams. It is interesting to note that the two servings of butter contributed over half, 29 grams of saturated fat to this day. The serving of chicken added another 16 grams. Without chicken and butter, this day would have a much healthier amount of saturated fat. Next, let us look at a typical American diet.

Figure 31 Graph of saturated fat in a typical American diet

This standard American diet is not very heart healthy. This diet will continue the progression of atherosclerotic plaque and heart disease. The 61 grams of saturated fat in this day far exceeds guidelines of 12, 17, or 24 grams. With 61 grams of saturated fat, this diet is double the American Heart Association's recommendation of 7% of calories as fat (it is 15%).

A fast food hamburger, a milkshake, and chicken were the major contributors of saturated fats in this diet, with over half of the saturated fats coming from these three foods. One doughnut and a cup of ice cream also contributed to the saturated fat content. Next, let us look at the Mediterranean diet below.

Figure 32 Graph of saturated fat in a Mediterranean diet

The Mediterranean diet is touted as a heart healthy diet. This diet will slow the progression of atherosclerotic plaque and heart disease when compared to a typical American diet. With 18 grams of saturated fats, this diet is not far over the American Heart Association's recommendation of 7% of calories as saturated fat (it is 7.8%). Olive oil and yogurt were the major contributors of saturated fats in this diet, with over half of the saturated fats coming from these two foods. Parmesan cheese and chicken also contributed to the saturated fat content. Next, let us look at a vegetarian diet that includes a large amount of dairy products and eggs.

Figure 33 Graph of saturated fat in a transitional vegetarian diet

This day's diet can be called a transition vegetarian diet as it is less healthy than most vegetarian diets. The 44 grams of saturated fat in this day far exceeds guidelines of 12, 17, or 24 grams. This diet has 17% saturated fat, more than double the recommended level. The two biggest contributors of saturated fat are cheese and potato chips, which contribute over 20 grams of saturated fat (almost half) to this day's diet. Ice cream, eggs, and milk also contributed another 15 grams of saturated fat. As we learn which foods are heavy contributors of saturated fats, we can achieve the ability to lower blood cholesterol with dietary changes. Next let us look at a whole food vegan diet.

Figure 34 Graph of saturated fat in a whole food vegan diet

This whole food vegan diet has only 3.7% of the calories as saturated fats. With a saturated fat content of about 9 grams, it has the potential to reverse fatty accumulations in the arteries. It is interesting to note that the avocado contributed most of the saturated fat to this day's diet. Almonds, bread, and salad dressing were all minor contributors of saturated fats. Next, let us look at a raw food diet high in fats from nuts and seeds.

Figure 35 Graph of saturated fat in a raw food vegan diet

This raw food vegan diet relies heavily on nuts and seeds for calories. Although the percent of fat as calories is quite high at 45%, the amount of saturated fat is just at the American Heart Association's recommended limit of 17 grams. This diet has about 6% of calories as saturated fat. The avocado is the highest contributor of saturated fats, closely followed by almonds, sesame seeds, and cashews. This diet would only be healthy for a very active person who could burn off the extra fats. Lastly, let us consider a therapeutic diet used to reduce cholesterol in patients with previous heart attacks.

Figure 36 Graph of saturated fat in a diet for preventing heart disease

The above diet is typical of Dr. Dean Ornish's program to help heart attack patients recover. The diet is very low in fat and has only 2 grams of saturated fats. This is only 1% of calories as saturated fat. This diet is rich in flavor and as satisfying as such a low fat diet can be. Diets such as this one have been instrumental in reversing heart disease and keeping heart attack victims alive for extended periods.

Structure of saturated fats

Saturated fatty acids all look very much alike. They each have an acid end and a methyl end. All of the carbon atoms are fully saturated with hydrogen atoms. This makes saturated fatty acids less likely to react with oxygen or other molecules than the other fatty acids. The only structural difference between the various saturated fatty acids is the number of carbon atoms.

Length of saturated fatty acids

Saturated fatty acids can be as short as 4 carbon atoms and as long as 30 carbon atoms. Common saturated fatty acids range from 12 to 18 carbon atoms long. Most natural fats, including saturated fats, have even numbers of carbon atoms. This is because they are built out of 2-carbon fragments.

There are some rare saturated fatty acids 32, 34, and 36 carbons long (not shown below). There are also little-known and rare saturated fatty acids with odd numbers of carbons from 3 to 35 carbons long (also not shown below).

Saturated Fat Name	Number of Carbon Atoms	Shorthand Notation	Source Examples
Butyric acid	4	4:0	4% in butter
Caproic acid	6	6:0	2% in butter, also palms
Caprylic acid	8	8:0	8% in coconut oil
Capric acid	10	10:0	5% in coconut oil
Lauric acid	12	12:0	50% in coconut
Myristic acid	14	14:0	17% in coconut oil
Palmitic acid	16	16:0	Most fats and oils
Stearic acid	18	18:0	12-25% in animal fats
Arachidic acid	20	20:0	1% in peanut oil
Behenic acid	22	22:0	3% in peanut oil
Lignoceric acid	24	24:0	1% in peanut oil
Cerotic acid	26	26:0	Carnauba wax
Montanic acid	28	28:0	Brown coal
Melissic acid	30	30:0	Beeswax

Figure 37 Chart of saturated fatty acids

Chart of saturated fatty acids (above). In the shorthand notation, the first number is the number of carbon atoms and the second number is the number of double bonds. Short chain, medium chain, long chain, and very long chain fatty acids are color coded. Please note that lauric acid is sometimes included in the long chain category.

The acid delta end and the methyl omega end

All fatty acids consist of a chain of carbon atoms. At one end there is a weak acid called a carboxyl group (COOH). This is why fatty acids have the word "acid" in their name. This acid end likes to hook up with glycerol to form a triglyceride. This acid end is referred to as the delta end.

Figure 38 The structure of a saturated fatty acid

The other end of the fatty acid consists of a methyl group (H₃C). This methyl end is referred to as the omega end of the fatty acid. Omega is the last letter in the Greek alphabet.

Enzymes that desaturate (insert a double bond in) fatty acids start their work from the delta end. This is why biochemists named the other end omega.

In a carbon chain, each carbon atom has room for two hydrogen atoms (see above). On a saturated fat, all of the carbon atoms are "saturated" with hydrogen atoms.

The most common saturated fatty acids in most diets are lauric acid, myristic acid, palmitic acid, and stearic acid. As you can see from the diagram below, they are all of similar structure except for chain length.

Figure 39 Structures of lauric, myristic, palmitic, and stearic acids

References:

(Fernandez, 2005) Fernandez, M. and West, K., "Mechanisms by which Dietary Fatty Acids Modulate Plasma Lipids," J. Nutr. 135:2075-2078, September 2005

(FNB, 2005) "Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients)," 2005, Food and Nutrition Board (FNB), Institute of Medicine.

(Hu, 1999) Frank B. Hu, et al., "Dietary saturated fats and their food sources in relation to the risk of coronary heart disease in women," American Journal of Clinical Nutrition, Vol. 70, No. 6, 1001-1008, December 1999.

(WHO, 1993) WHO/FAO 1993, "Fats and oils in human nutrition: Report of a joint expert consultation"

Chapter 5: Monounsaturated Fats

Summary

Most people think of olive oil when they think of monounsaturated fats. Oleic acid is the common monounsaturated fat that is named after olives. There are over 20 monounsaturated fats in food. High-oleic-safflower oil, olive oil, and canola oil are high in oleic acid, with over half of their oils in this form. Oleic acid is the most abundant fatty acid in food and in human fat. Oleic acid is considered to be a healthy fatty acid, especially when compared to the saturated or trans fatty acids.

All monounsaturated fatty acids have exactly one double bond. Oleic acid is called an omega-9 because the double bond is nine carbon atoms from the omega end of the fatty acid. This double bond changes the shape of the fatty acid so that cell membranes are more permeable to blood sugar and cholesterol. This reduces the risks of diabetes and heart disease compared to the saturated fatty acids. The double bond is, however, more susceptible to oxidation. This makes it more important for monounsaturated fatty acids to be protected with vitamin E.

Oleic acid can be converted by hydrogenation into stearic acid or into trans oleic acid. Trans oleic acid acts more like a saturated fat than a monounsaturated fat.

Oleic acid

Olive oil is a rich source of the monounsaturated fatty acid oleic acid. Oleic acid is the monounsaturated fatty acid that was named after olive oil. Oleic acid is the most abundant monounsaturated fatty acid. In fact, it is the most abundant fatty acid of any type. The chart below shows the amount of oleic acid in some common nuts and seeds.

Figure 40 Graph of oleic acid in nuts and seeds

Coconut meat is low in oleic acid because it is mostly saturated fat. English walnuts and flax seeds have less oleic acid because of their high content of essential fatty acids. Macadamia nuts have 58% oleic acid and about 25% palmitoleic acid, another monounsaturated fatty acid. This makes macadamia nuts the most monounsaturated nut with 83% monounsaturated fat. The amount of oleic acid in meat, chicken, and fish is quite low, about one-tenth of the amount of oleic acid in nuts. In the chart below we look at the oleic acid in common fats and oils.

Figure 41 Graph of oleic acid in common oils

In the graph above it is clear that safflower oil, olive oil, and canola oil are especially rich in oleic acid. Oleic acid makes up over half of the fatty acids in these oils. Lard is often thought of as a saturated fat, however lard contains over 41% oleic acid.

Double bonds

The word monounsaturated means that there is one bond between carbon atoms that is not saturated with hydrogen atoms (please see the figure below). All of the other carbon atoms are saturated with hydrogen atoms.

Figure 42 The structure of unsaturated bonds

The carbon atoms in a fatty acid each have four electrons so four bonds are possible. In a carbon chain, two of these bonds are needed to link to the other carbon atoms that come before and after. This leaves two bonds open for hydrogen atoms. However, in an unsaturated bond, the carbon atoms link up with a double bond. This leaves only one bond available for a hydrogen atom on each of these carbon atoms.

Below we see the difference between the monounsaturated oleic acid and a fully saturated stearic acid. The two fatty acids are the same length, but the unsaturated double bond occurs only in the monounsaturated oleic acid.

Figure 43 The structures of oleic acid and stearic acid showing a double bond

Omega-9 fatty acid

The single double bond in oleic acid is located in the center of the 18 carbon chain. This puts it 9 carbon atoms from the omega end and makes it an omega-9 fatty acid. The double bond creates a bend in the fatty acid. The fully saturated fat with 18 carbon atoms is called stearic acid.

Figure 44 3-D structure drawings of oleic acid and stearic acid

As you can see above, the saturated stearic acid is straight, while oleic acid (on the right) has a bend in the middle. In this figure, the gray atoms are carbon and the white atoms are hydrogen.

Double bonds and oxidation

The number and placement of double bonds in fatty acids are very important. With a double bond, two bonds are "up for grabs." These extra bonds are very important because another element can come along and react at the unsaturated point in the carbon chain of the fatty acid. The double bond is more likely to react with other elements than a saturated bond. For instance, oxygen could react with this double bond, creating rancidity. This process of oxygen bonding to an unpaired electron of carbon and creating rancidity is an example of lipid peroxidation. Antioxidants such as vitamin E prevent this oxidation of double bonds. The more double bonds in a fatty acid, the more susceptible it is to oxidation, unless it is protected by vitamin E.

Cis and trans configurations

In a double bond, the two hydrogen atoms can be on the same side of the fatty acid chain, or on opposite sides. The natural form of oleic acid has the two hydrogen atoms on the same side of this fatty acid. This is called the "cis" configuration. If the hydrogen atoms are on opposite sides, this is called the "trans" configuration. Trans oleic acid can be formed in the industrial processing of oil called hydrogenation. During hydrogenation, many of the oleic fatty acids will be filled with hydrogen, thus eliminating any double bonds. This transforms oleic acid into stearic acid. Some of the oleic fatty acids will be deformed into the trans configuration. Please check the following figure to see the difference.

Figure 45 Structural differences between cis and trans double bonds

Biological importance of cis and trans bonds

While cis-oleic acid is naturally bent in the middle, trans-oleic acid is straight. This bend is important when oleic acid is incorporated into cell membranes. The bent leg of natural cis-oleic acid prevents tight packing of the fatty acids together. The trans form of oleic acid packs together in a cell membrane much like a saturated fatty acid. This more tightly packed cell membrane has less fluidity. Trans fatty acids in cell membranes make it more difficult for the cell to take in glucose (blood sugar) from the bloodstream. This contributes to decreased insulin sensitivity and type two diabetes.

The tightly packed membrane also decreases the ability of the cell to take in cholesterol. In this way, trans fatty acids contribute to higher blood cholesterol and coronary heart disease. The diagram below shows a three dimensional representation of the natural cis-oleic acid, trans-oleic acid, and the saturated fat stearic acid. Notice how closely the trans form of oleic acid resembles the fully saturated stearic acid.

Figure 46 3-D drawings of cis and trans double bonds

Common monounsaturated fatty acids

Oleic acid is found in abundance in most edible oils. It is found in animal fats as well as vegetable oils. Oleic acid occurs naturally in greater quantities than any other fatty acid. Oleic acid is also the most abundant fatty acid in human fat; it makes up about half of the fatty acids in human fat (Kokatnur, 1979). Oleic acid is written in shorthand notation as 18:1 n-9. Shorthand notation is good to know about as it is often used in scientific journal articles.

Shorthand notation

The shorthand notation 18:1 n-9c starts with the number of carbon atoms, followed by the number of double bonds after the colon. For monounsaturated fatty acids the number of double bonds is always 1. The "n" followed by a dash and a number indicates the position of the first double bond, counting from the omega end. C is for the natural cis isomer and t is for the trans isomer.

Other monounsaturated fatty acids

Palmitoleic acid makes up about one quarter of the fat in macadamia nuts and is found in many other foods. Palmitoleic acid is a monounsaturated fatty acid. It is 16 carbon atoms long with the double bond 7 carbons from the omega end. This is written in shorthand notation as 16:1 n-7c.

Petroselinic acid is a monounsaturated fat with 18 carbon atoms. Its first double bond is 12 carbon atoms in from the omega end. Shorthand notation for petroselinic acid is 18:1 n-12c. It is found in the seeds of parsley (petroselinum sativum), coriander, and fennel. Petroselenic acid is called a positional isomer of oleic acid because it is the same except for the placement of the double bond; please refer to the following figure.

Figure 47 Structural differences with positional isomers in two fatty acids

Gadoleic acid is a monounsaturated fat with 20 carbon atoms. Gadoleic acid is found in small amounts in some fish fats. It makes up about one tenth of the oil of rapeseed. It can also be found in peanut oil and lard. Since its double bond is 11 carbon atoms from the omega end, the shorthand notation is 20:1 n-11.

Cetoleic acid was first found in white whale blubber. It makes up almost one quarter of the oils in herring. It is also found in other fish such as sardines, anchovies, and cod. This 22 carbon monounsaturated fatty acid has one double bond at position 11 from the omega end (22:1 n-11c).

Erucic acid is a monounsaturated fatty acid that makes up almost half of the fatty acids of rapeseeds and mustard seeds. The amount of erucic acid in rapeseed was lowered to 2% by using mutagenic chemicals, which developed a new strain called canola (Canada oil low acid). There are some toxicity questions about erucic acid, especially with infants. Erucic acid is valuable for high temperature lubrication and for drying oil paints. Erucic acid is 22:1 n-9c in shorthand notation.

Nervonic acid is an omega-9 monounsaturated fat with 24 carbon atoms (24:1 n-9c). It is needed in certain nerve cells. It is used in making the myelin sheath of nerves. It is thought to be used in the nerve cell protective layer and also for cell recognition and signaling. Certain fatty tissue (sphingomyelin) from people with multiple sclerosis have been found to have decreased levels of nervonic acid (Sargent, 1994).

Common and uncommon monounsaturated fatty acids

The chart below lists monounsaturated fatty acids with their shorthand notation and some examples of sources.

Monounsaturated Fat Name	Number of Carbon Atoms	Shorthand Notation	Source Examples
Caproleic acid	10	10:1 n-1	Butter
Linderic acid	12	12:1 n-8c	Lindera shrub
Lauroleic acid	12	12:1 n-3c	Dairy products
Obtusilic acid	14	14:1 n-10	Plumeria obtusa leaves
Tsuzuic acid	14	14:1 n-10c	Seeds of lindera obtusiloba
Physeteric acid	14	14:1 n-9c	Sardines
Myristoleic acid	14	14:1 n-5c	Nutmeg
Palmitoleic acid	16	16:1 n-7c	Macadamia nuts
Palmitelaidic acid	16	16:1 n-7t	Sea Buckthorn Seeds
Petroselinic acid	18	18:1 n-12c	Parsley, fennel, and coriander
Oleic acid	18	18:1 n-9c	Many common oils
cis-Vaccenic acid	18	18:1 n-7c	Mango fruit
Vaccenic acid	18	18:1 n-7t	Butter
Gadoleic acid	20	20:1 n-11	Cod liver oil, rapeseed, peanut oil
Gadelaidic acid	20	20:1 n-11t	fish
Cetoleic acid	22	22:1 n-11c	Herring
Erucic acid	22	22:1 n-9c	Rapeseed, Mustard seed
Brassidic acid	22	22:1 n-9t	Rapeseed
Nervonic acid	24	24:1 n-9c	Broccoli, honesty seeds
Ximenic acid	26	26:1 n-9c	Ximenia caffra oil
Lumequic acid	30	30:1 n-9c	Ximenia caffra oil

Figure 48 Chart of monounsaturated fatty acids with examples

References:

(Kokatnur, 1979) MG Kokatnur, MC Oalmann, WD Johnson, GT Malcom and JP Strong, "Fatty acid composition of human adipose tissue from two anatomical sites in a biracial community" American Journal of Clinical Nutrition (November 1979) 32 (11): 2198.

(Sargent, 1994) Sargent JR, Coupland K, Wilson R. "Nervonic acid and demyelinating disease." Med Hypotheses. 1994 Apr;42(4):237-42.

Chapter 6: Essential Fats

Summary

There are only two essential fatty acids. One of them, linoleic acid, is easy to find in food. In fact, many Americans get too much of this essential fatty acid. Linoleic acid is the only essential fatty acid in the omega-6 family. The other essential fatty acid is alpha-linolenic acid, which is the only essential fatty acid in the omega-3 family. To be essential, these two fatty acids must be in the natural cis configuration. Other fatty acids are not essential in the diet because we can make them inside our bodies.

Nuts, seeds, beans, and canola oil can be good sources of essential fatty acids. Any fat can be burned for energy, but these essential fatty acids are needed to allow our bodies to regulate inflammation, blood clotting, and pain. On the other hand, these essential fatty acids are delicate and vulnerable to damage from light, heat, and exposure to oxygen. While still inside food, such as inside a seed, the delicate oils are protected. A high content of essential fatty acids is one of the important ways to choose a healthy fat.

The meaning of essential

To be essential, a nutrient must meet two criteria. First, it must be impossible for the nutrient to be created inside the body. Secondly, the nutrient must be needed to prevent death or serious illness.

Only two fatty acids meet both of these requirements. These are alpha-linolenic acid (ALA) and linoleic acid (LA). Please remember the two abbreviations ALA and LA, as they will be used extensively in this chapter. Please note that although ALA is a common abbreviation, some other authors use the abbreviation LNA for alpha-linolenic acid.

Activation of essential fatty acids

Many essential nutrients need to be converted to their active form before performing their function. This conversion process can allow our bodies to convert just the amount needed and in the locations needed. Vitamin D is one example, as it needs to be converted into calcitriol to be effective. With vitamin D, this conversion is accomplished when and where needed. Many of the B-vitamins need to be in their active enzyme form to perform their functions. Essential fatty acids also need to be converted to their active forms before they are able to perform their functions. Chapters eleven and twelve will discuss the active forms of essential fatty acids.

ALA and LA are needed inside our bodies

Like other fatty acids, ALA and LA can be burned for energy. Unlike other fatty acids, only these two can be elongated, desaturated, and oxygenated into eicosanoids. Eicosa means twenty in Greek and eicosanoids are all fatty acids with 20 carbon atoms. Eicosanoids are powerful, short-acting regulators of blood clotting, the immune system, and other crucial factors. Eicosanoids act locally, inside a cell and on surrounding cells. With the right balance of dietary essential fatty acids we can have the right balance of eicosanoids.

Figure 49 Important roles for essential fatty acids and their derivatives

Text Box: Essential fatty acids and their derivatives are important:
* For controlling blood clotting.
* In arterial constriction and dilation.
* In immune function.
* In the early development of the nervous system.
* To prevent memory loss and learning disabilities.
* In the retina of the eye.
* To adjust the fluidity, flexibility, permeability of cell membranes.
* In cell membranes for signaling and the activity of membrane bound enzymes.
* In the regulation of gene expression, especially the genes controlling fatty acids. Essential fatty acids must first be elongated before performing many of these functions.

It was not until after 1950 that the need for both essential fatty acids was firmly established. The ability of our bodies to use stored essential fatty acids complicates the detection of symptoms of deficiency. When dietary ALA and LA are not available, our bodies can remove and use ALA and LA that are stored in triglycerides in fat tissue. We can also pull out and use elongated essential fatty acids from phospholipids in cell membranes.

One clinical sign of essential fatty acid deficiency is decreased growth in infants and children. Other clinical signs of deficiency include dry scaly rashes, increased susceptibility to infection, and poor wound healing. Linoleic acid is needed as a part of the water barrier in the membranes of skin cells. Deficiency of ALA can result in visual problems and problems with sensory nerves.

Signs of essential fatty acid deficiency can develop in as little as one week under certain conditions of parenteral (intravenous) feeding (Stegink, 1977). ALA and LA deficiencies can develop with parenteral feeding with formulas that are fat free and also contain glucose. Continuous glucose suppresses insulin and the release of stored essential fatty acids.

Other long-chain polyunsaturated fatty acids

It is commonly reported that members of the omega-3 and omega-6 families other than ALA and LA are essential fatty acids. This mistake is most often made with eicosapentanoic acid (EPA) and docosahexanoic acid (DHA). It is true that these long-chain fatty acids are needed for life and health. They are not essential because we are capable of creating both EPA and DHA inside our bodies.

All of the necessary long-chain omega-3 and omega-6 fatty acids can be made in our bodies. Starting either with ALA or LA, these essential fatty acids are elongated with elongase enzymes. They are desaturated with desaturase enzymes.

DHA is vital for proper development of an infant's mind and eyes. Infants under 6 months old, especially premature infants, may not be able to make their own DHA. For infants, DHA may well be an essential nutrient. Since DHA is normally contained in mother's milk, this dependence is only noticed with DHA-deficient infant formulas.

Linoleic acid, the easy essential fatty acid

Outside of nuts, seeds, and oils, even the easy-to-find linoleic acid (LA) is a bit elusive. To prevent overt signs of deficiency we need at the very least a minimum of one percent of LA. It is estimated that we need from 5 to 8 percent of our calories as LA for excellent health (WHO, 1993). The European Commission recommends an LA fatty acid intake of 4 to 8 percent of energy. We need closer to eight percent if our diet contains excesses of the saturated fats that are often found in meat and dairy products. Dietary intake of trans fatty acids can also raise our need for LA. We may need only about four percent of our calories as LA if our diet is low in saturated fats.

As an average need, let's figure on needing about seven percent of our calories as LA. In an average day with 2200 calories, this works out to a daily need of about 17 grams of linoleic acid. This figure of 17 grams is based upon fat containing 9 calories (kcal) per gram. Also, the 2002 recommendation from the Institute of Medicine is 17 grams of LA for adults 19-50 years of age.

It is not healthy to take in too much linoleic acid. A maximum of about 10% of calories is considered safe. The problem with too much LA is twofold. First, too much LA interferes with the elongation of the other essential fatty acid, ALA. Secondly, too much of any polyunsaturated oil will increase susceptibility to oxidation. The more double bonds in a fatty acid, the more reactive it is with oxygen. Reactive oxygen species degrade polyunsaturated oils. This lipid peroxidation can form reactive products such as malondialdehyde. Malondialdehyde can mutate DNA with a potential for increasing risks of cancer.

Polyunsaturated oils need vitamin E for protection from oxidation. Polyunsaturated fatty acids should be protected from light, heat, and exposure to oxygen. This is best accomplished by eating whole foods rather than refined oils.

Food sources of linoleic acid

The essential fatty acid linoleic acid (LA) is in limited supply in food. As you can see from the following graph, animal products and grains are poor sources. Nuts and seed are generally good sources. Most fruit and vegetables are also poor sources. Avocados and olive are exceptions with moderate amounts of LA.

Figure 50 Graph of linoleic acid content of some common foods

Linoleic acid is abundant in many common culinary and cooking oils. For most of the oils in the following graph, one ounce is equivalent to two tablespoons. When these oils are used several times a day, it is easy to get too much.

Figure 51 Graph of linoleic acid content of some common oils

Linoleic acid in common diets

In a Mediterranean diet, the linoleic acid content was a little over 12 grams in one day. Please remember that the optimal range of intake of LA is 10 to 20 grams daily. The linoleic acid in this diet was mostly from olive oil. Looking at an Atkin's diet, the linoleic acid was a little over 14 grams. In this Atkin's diet, most of this LA comes from corn oil and chicken. In a typical American diet, the LA content was about 15 grams. In a diet based upon the Zone diet, the LA content was about 14 grams. In one transitional vegetarian diet the LA came out to almost 30 grams. Potato chips alone accounted for about two-thirds of this high LA intake. In a whole food vegan diet, the amount of LA was about 12 grams. Most of the LA in this diet came from avocados, salad dressing, and nuts.

As you can learn from the diets analyzed in the above paragraph, it is quite easy and normal to get enough linoleic acid in many common diets. The diet lowest in LA was a very low fat diet designed by Dr. Dean Ornish for recovery from heart disease. This diet had only 4 grams of LA. Even though this diet is very low in saturated and trans fats, the 4 grams of LA seems very low as it is only 2.5 percent of calories. This is lower than the 4 to 5 percent of calories normally recommended as the minimum amount of dietary LA.

The structure of linoleic acid

Linoleic acid is the least unsaturated of all of the polyunsaturated oils. LA has two double bonds. Two double bonds means that there are two bonds not saturated with hydrogen atoms in this fatty acid. As you can see from the structure diagram below, two hydrogen atoms are "unsaturated" (missing) at each of the double bonds. The first double bond is six carbons from the omega end, thus making it an omega-6 fatty acid.

Figure 52 The structure of linoleic acid showing the double bond at omega-6

Natural fatty acids have double bonds separated by three carbon atoms. Linoleic acid has double bonds at the 6 and 9 position from the omega end. The shorthand notation of natural cis linoleic acid is (18:2 n-6c). This shorthand notation means that the fatty acid is 18 carbon atoms long, has 2 double bonds, is an omega-6, and is in the natural, cis configuration.

If the two hydrogen atoms at a double bond were on opposite sides of the molecule, then it would be in a trans configuration and written (18:2 n-6t). In the trans configuration, the molecule would not be bent at the trans double bond. Trans linoleic acids are not considered essential fatty acids.

Alpha-Linolenic acid, the hard-to-get essential fatty acid

Optimal amounts for the harder-to-get alpha-linolenic acid (ALA) are estimated at about 1 to 2 percent of calories. In a typical 2200 calorie (kcal) diet, this would be 22 to 44 calories (kcal) of ALA. This is equivalent to 2.4 to 5 grams of ALA daily. As we have seen, we need about 17 grams of Linoleic acid with the same caloric intake. This ratio of 5.5 to 7 times as much LA as ALA is considered healthy, although 4 times as much LA as ALA would be even healthier.

Food sources of ALA

This hard-to-get essential fat, ALA, is only found in small amounts and only in certain foods. Even the seemingly low amount of two grams of ALA is difficult to obtain from food. Fresh walnuts are about the only nuts, indeed one of the only foods, with high amounts of this hard to find ALA.

Figure 53 Food sources of the essential fatty acid ALA

Text Box: Walnuts are the best food source of the essential ALA with ¼ cup supplying enough for a day.
It takes about ten servings of avocados, spinach, or whole grain bread to get enough ALA for a day.
Other food choices have so little that you would need an unrealistic 20 or more servings.

In a sample diet containing food choices from all of the food groups, only servings of bread, spinach, and avocados supplied even one-tenth of the daily need for ALA. Ground flax seeds are very high in ALA. So, to get enough ALA we need to either eat some walnuts or flax seeds, or include some oils that are high in ALA.

Spinach and other leafy green vegetables have a good ratio of linoleic acid to ALA, but you would need to eat about one gallon of cooked spinach to get just one day’s worth of ALA. Still, spinach and other leafy green vegetables do contribute to daily ALA intake. Purslane, a common weed, has some ALA, but again, one cup of cooked purslane has only a fraction of a gram of fat. It would take an unrealistic 20 servings to fulfill your daily need of ALA.

Some authors have stated that wild game is a good source of ALA because wild animals eat mostly grasses, rather than grains. However, a study of four wild game meats shows at most a tenth of a gram of ALA in a serving (USDA, 2008). Meat simply does not have enough ALA to satisfy our needs, regardless of the source. A serving of wild game meat also has less than one gram of linoleic acid, and we need 17 grams of this, so even wild meat is a very poor source of the essential fatty acids.

ALA in oils and fats

While linoleic acid is very easy to obtain from most vegetable or seed oils, ALA is rare. The only common oils with a high content of ALA are flax oil, canola oil and soybean oil.

Figure 54 Graph of ALA content of some common oils

In the graph above, the amount of ALA is shown for 2 tablespoons of the oil or fat. Two tablespoons of soybean or canola oil is close to the amount of ALA needed in one day (2.4g).

Also shown in the chart above are the relative amounts of ALA to the other essential fatty acid, linoleic acid (LA). Ideally, the ratio of LA to ALA should be about 2 to 1 to 4 to 1. Ratios up to 7 to 1 are also reasonably healthy. When an oil has ten times or more LA than it has ALA, it is unbalancing. Higher amounts of LA encourage the production of certain undesirable eicosanoids while inhibiting more desirable eicosanoids.

ALA in some common diets

Let us consider the amount and sources of ALA in some common diets. In a Mediterranean diet about half of the ALA came from olive oil and beans. This diet had 1.3 grams of ALA, which is barely enough compared with the 2.4 grams needed daily. An Atkin's diet had a deficient amount of only 0.8 grams of ALA in one day. Bacon and chicken supplied about half of the tiny amount of ALA in this diet. In a typical American diet, the amount of ALA was 1.5 grams. Most of this rather low amount was found in thousand island salad dressing and chicken. On a Zone diet, the amount of ALA was only 0.4 grams. One serving of mayonnaise accounted for half of this tiny amount. Looking at a transitional vegetarian diet, the ALA was 1.4 grams. This is a little over half of the daily need. Potato chips and mayonnaise accounted for over half of this amount of ALA. A vegan, whole food diet had just 1.1 grams of ALA. Avocado, beans, and salad dressing supplied most of this ALA in this diet.

Diet Name	Amount of LA	Amount of ALA	Ratio LA to ALA	Ratio of LA to ALA with 2 T flax powder
Mediterranean	12	1.3	9.4	2.9
Atkin's	14	0.8	18	3.7
American Diet	15	1.5	10	3.4
Zone	14	0.4	36	4.2
Transitional Vegetarian	29	1.4	21	6.5
Vegan Whole Food	12	1.1	11	3
Very Low Fat Ornish	4.2	0.5	8.4	1.4
Raw Vegan	32	2.3	14	6

Figure 55 Chart of LA and ALA in eight diets with added flax powder

The chart above shows some common diets and the essential fatty acid amounts. The only diet to have enough ALA was the raw vegan diet. Beans (1.1g), spinach (0.5g), and avocados (0.3g) were the major contributors of ALA to this diet. As the chart above shows, getting the optimal ratio of LA to ALA is difficult. Only the low fat Ornish diet and the Mediterranean diet had fair ratios of the essential fatty acids, although the American diet and vegan whole food diet have acceptable ratios.

When two tablespoons of ground flax seeds are added to these diets, the ratio of LA to ALA becomes excellent. Please check the right column of the above chart to see how the ratios are improved with the addition of flax powder. The flax powder also raises the amount of ALA by 3.2 grams in each of these diets.

Structure of ALA

Alpha-linolenic acid is 18 carbon atoms long, just like linoleic acid, oleic acid, and stearic acid. It has three double bonds instead of the two that linoleic acid has. Three double bonds create more of a curved shape, rather than a bent shape. The big difference is the extra double bond in the omega-3 position. Please see the figure below to get more familiar with the structure of ALA. The shorthand notation for natural ALA is (18:3 n-3c). The n-3 means that it is an omega-3 fatty acid. The 3 after the colon indicates that it has 3 double bonds. The c stands for cis, the natural form of ALA.

Figure 56 Structure of alpha-linolenic acid

ALA has three double bonds. This makes it more susceptible to rancidity and oxidation than linoleic acid. You may have noticed how sweet walnuts can taste when freshly shelled. You may have also noticed how bitter walnuts can be if they are old. Oxidized ALA can cause bitterness and a rancid smell. This susceptibility to rancidity is why oils high in ALA are not used for frying without alteration. Soybean oil has a high content of ALA. The soybean oil used for frying is partially hydrogenated to reduce the ALA content. Partially hydrogenated soybean oil is one of the oils most often used for frying doughnuts and French fries. During hydrogenation, some of the essential fatty acids are converted to stearic acid or trans isomers.

Why ALA and LA cannot be made in the body

Human enzymes called desaturases can insert double bonds into fatty acids. These desaturases are limited in mammals. They cannot insert a double bond in the omega-3 or omega-6 position of 18-carbon or longer fatty acids. Humans have three desaturase enzymes that can insert double bonds into fatty acids. These are delta-5 desaturase, delta-6 desaturase, and delta-9 desaturase. Delta-9 desaturase is also known scientifically as Stearoyl CoA Desaturase. The desaturases in mammals work from the delta end of the fatty acid.

Delta-5 desaturase can reach just 5 carbon atoms from the delta end of a fatty acid. In the figure below, delta-5 desaturase is shown to insert a double bond at the omega-15 position of a 20-carbon fatty acid. Delta-6 desaturase can reach just 6 carbon atoms from the delta end. This allows delta-6 desaturase to reach to the omega-12 position in an 18-carbon fatty acid. Delta-9 desaturase can reach to the omega-9 position of an 18-carbon fatty acid. Thus, delta-9 desaturase can create oleic acid (18:1 n-9) from stearic acid (18:0).

Figure 57 Delta-5 desaturase and the structure of EPA

In the figure above, you can see how desaturase enzymes work. The numbers 1-5 are positions of carbon atoms counting from the delta end. The figure above shows the last step in the biosynthesis of EPA from ALA.

None of these desaturase enzymes can insert a double bond at the omega-3 or omega-6 position of a fatty acid of 18 or more carbon atoms in length. This is why ALA and LA are not able to be made inside our bodies.

References:

(Stegink, 1977) Stegink LD, Freeman JB, Wispe J, Connor WE. "Absence of the biochemical symptoms of essential fatty acid deficiency in surgical patients undergoing protein sparing therapy." Am J Clin Nutr. 1977;30(3):388-393.

(USDA,2008) USDA Food Composition Database Release 21, September 2008.

(WHO, 1993) Expert Consultation on Fats and Oils, FAO/WHO, 1993.

Chapter 7: Trans Fatty Acids, The Bread and Butter of Disease

Summary

Trans fatty acids have at least one double bond in a twisted, trans configuration. This straightens the fatty acid, changing the effects on health and disease. Trans fatty acids are detrimental to health and the healthiest amount to include in the diet is zero. Trans fatty acids have been found to increase bad (LDL) cholesterol, while lowering the good (HDL) cholesterol. They also raise blood triglycerides. The effect of trans fats is to raise the risk of heart attacks. There is an emerging connection between dietary trans fatty acids and the risk of type II diabetes.

There are two different sources of trans fats. Most trans fats are found in oils that have been industrially hydrogenated. Another significant source is from dairy products, and to a lesser extent from beef. In some countries the majority of trans fats come from these animal products. In America, most of the trans fats in the diet come from baked goods. About 21% come from dairy products and beef. French fries and potato chips are a significant source. Attempts to lower trans fats in food that substitute tropical oils or animal fats for trans fats increase the risk of heart disease because of the increased amount of saturated fats.

Introduction

Trans fatty acids start out as normal fatty acids, such as oleic acid or linoleic acid. These normal unsaturated fatty acids are altered either by industrial hydrogenation of oils or by bacteria in the digestive tract of cows, sheep, and goats. Some trans fatty acids are introduced into oils during the refining process for edible oils.

The altered trans fatty acids have undesirable effects on health. Trans fatty acids increase the "bad" blood cholesterol (LDL) a bit more than saturated fatty acids do. Because trans fatty acids are found in most diets at one-tenth the amount of saturated fatty acids, it is the saturated fatty acids that cause the majority of undesirable changes in blood cholesterol. The healthiest amount of trans fatty acids in the diet of a well-nourished person is zero.

Dietary sources of trans fatty acids

Americans eat twice as much trans fatty acids as all other food additives combined. There are two dietary sources of trans fatty acids. One source is partially hydrogenated vegetable oils. The other source is from meat and dairy products from ruminant animals such as cows, goats, and sheep. The high heat of physical refining creates trans fatty acids even without hydrogenation. The level of trans fatty acids in corn, soybean, and canola oils increased to a substantial extent (1–4%) after physical refining, even without hydrogenation (Farrari, 1996).

Figure 58 Chart of trans fat from dairy products versus hydrogenation in 5 countries

Text Box: % Trans fats from Ruminant Sources % Trans fats from Hydrogenation
Australia 60 % 40 %
New Zealand 41 % 59 %
Sweden 19 % 81 %
Canada 50 % 50 %
United States 21 % 79 %
Average 38 % 62 %

As you can see from the above box (Skeaff, 2009), the amount of trans fatty acids from ruminant sources, such as beef, mutton, and dairy products varies widely between countries. The amount of trans fatty acids from hydrogenation also varies widely between countries. Countries such as Australia derive much of their fat from animal products, so their intake of ruminant trans fatty acids is higher. In the United States, much of the fat consumed is from partially hydrogenated oils, so this is the major source of trans fatty acids. The amount and type of trans fatty acids also vary widely between different foods.

Average total trans fatty acid intakes from both sources range from a low of 0.6% of calories in Australia to a high of 4.2% of calories in Iran. For adults, 1% of total energy corresponds to about 2.5 g of trans fatty acids. Looked at in grams, the range of daily intake of trans fatty acids is between 1.5 grams and 10.5 grams.

As we shall see, the health damage from trans fatty acids, gram for gram, is somewhat worse than the health damage from saturated fatty acids. However, the amount of saturated fatty acids in many diets is about ten times the amount of trans fatty acids. Trans fatty acid intake per day is often from 2 to 5 grams (about 1-2% of energy). Saturated fatty acid intake per day is often 25 to 44 grams (about 10-18% of energy). This makes saturated fatty acids a much more significant contributor to heart disease than trans fatty acids. We must be careful as we reduce the amount of trans fatty acids in our diet that we do not increase our consumption of saturated fats from tropical oils or animal fats.

Alternatives to partially hydrogenated oils

The ubiquitous presence of partially hydrogenated vegetable oils throughout the global food supply in bakery products, deep-fried fast foods, snack foods, confectionery products, and table spreads attests to their commercial value and convenience.

Frying

Manufacturers use partially hydrogenated oil for deep frying because it resists rancidity and leaves a crisp product. Deep frying is especially important in the fast food business. Oils with a high alpha-linolenic acid content, such as soybean and canola oils, are unstable during storage and are readily oxidized. This oxidation contributes to a rancid, fishy flavor in fried foods that is undesirable. The partially hydrogenated versions are stable and have much less of the essential fatty acids to go rancid.

It is possible to use engineered canola or other oils for frying. The canola oil is either bred or genetically engineered to have less than 2% of alpha-linolenic acid and a high content of the monounsaturated oleic acid. At this time these "designer oils" are in short supply and cost about twice as much as cheaper alternatives. Price is especially important in frying oils because of the sheer quantity used. Deep fried fast foods are major contributors to obesity and heart disease—no matter what oils they are made with.

Snack foods

Manufacturers of snack foods, such as potato chips, need an oil that imparts crispness to the product. The vegetable oils are hydrogenated more than the frying oils to become harder at room temperatures. Partially hydrogenated cottonseed oil is commonly used as it starts out with about 25% saturated fatty acids. Cottonseed oil is a little more expensive than other frying oils, so it is usually blended with other partially hydrogenated oils.

Designer oils without trans fatty acids, with a higher content of oleic acid, and with a low content of essential fatty acids are available for frying snack foods. The higher price of these oils is a problem for manufacturers. Although salty, greasy snack foods sell well, they are not desirable in the food supply because of their contribution to obesity and heart disease—no matter what oils they are made with.

Bakery products

Bakery products, cakes, bread, crackers, pies, cookies, and so on, are also often formulated with partially hydrogenated vegetable oils. With these products, the amount of oil used is less, so the substitution of more costly blended designer oils without trans fatty acids is more feasible. If these bakery products were made with whole grains and healthful oils, they could become a food with healthful effects instead of the current health-damaging effects.

The risks of reducing trans fats

At this time manufacturers are reformulating their products to reduce trans fatty acids from hydrogenation.

Palm and other tropical oils

The cheapest and most available substitute for hydrogenated oils is palm oil. Unfortunately, palm oil is almost 50% saturated, while the partially hydrogenated soybean oil that it is replacing is only 16% saturated. Coconut oil is even more saturated at 87% saturation. Instead of reducing the burden of atherosclerosis and heart disease, these substitutions will increase the risk of heart disease.

Animal fats to replace hydrogenated oils

Manufacturers may also choose animal fats to replace the partially hydrogenated oils in their products. In some areas animal fats are cheap and available. Common choices are butter and lard. Butter averages about 51% saturated fatty acids and lard averages about 39% saturated fatty acids. In addition, these animal products contain small, but significant amounts of trans fatty acids. When these heavily saturated fats are substituted for hydrogenated soybean oil, the risk of heart attacks increases.

Designer oils

When oils are partially hydrogenated, trans fatty acids are formed. When oils are fully hydrogenated, they are fully saturated. There are no double bonds, so there are no trans fatty acids. When linoleic acid, alpha-linolenic acid, or oleic acid are fully saturated, they become the saturated fat stearic acid. This hard fat without trans fatty acids can then be blended with other vegetable oils for the proper firmness and melting properties. Care must be taken that the replacement oils are not so high in saturated fats that they negate the good effects of reducing trans fats.

Choosing food low in trans fatty acids

It is difficult to estimate the amount of trans fats consumed using dietary analysis and food composition tables. Many countries do not include trans fats in their food composition tables. A few countries, including the United States, do include trans fat. Unfortunately, few foods have been analyzed, so the tables are incomplete. Also, manufacturers are constantly changing the fats used, sometimes with variations in regional areas.

Worldwide variation in trans fatty acid intake

There is a wide variation worldwide in the trans fatty acid contents of similar foods. For instance, McDonald’s French fries from the Netherlands had less than 4% trans fatty acids in comparison with a average of 20% trans fatty acids in French fries from six different cities in the United States (Katan, 2006). The variation of trans fatty acid amounts between countries of a Kentucky Fried Chicken meal of French fries and chicken nuggets was even larger, with less than 1 gram of trans fatty acids in Germany and India and more than 20 grams in Hungary and Bulgaria (Stender, 2006).

Figure 59 Major sources of trans fats in America

Trans fats in food in America

In the United States, bakery products—including bread, cakes, crackers, pies, cookies, and so on—are the major source of industrially produced trans fatty acids in the diet. According to the Food and Drug Administration, in 2003, these baked products account for about 40% of the trans fatty acids in the diet. Surprisingly, 21% of the trans fats in American diets come from animal products—mostly dairy products, with a little from beef, and lamb. Margarine is a major contributor at 17% of the trans fats in American diets. Fried potatoes and snack food account for another 13% of American trans fatty acid intake.

Labeling deceit

Avoiding trans fatty acids by reading labels can be tricky. In the United States, if a food has less than half a gram of trans fatty acids per serving, it can be labeled as "trans fat free." Manufacturers often manipulate the serving size so that they can include this "trans fat free" claim on their products. It is not uncommon to see spreads made with partially hydrogenated soybean and cottonseed oil labeled "trans fat free." Many grams of trans fatty acids per day can be consumed when eating "trans fat free" foods. The best way to avoid trans fatty acids is to avoid products with the words "partially hydrogenated" in the ingredient list. Restaurant food does not always list ingredients, so disclosure is more difficult.

Absorption and metabolism of trans fatty acids

Trans fatty acids are absorbed from the digestive system just like other fats. Absorption is about 95% efficient, which is similar to other fats. Trans fats are stored in adipose tissue in triglycerides as are other fats. Trans fatty acids are burned for energy in the same manner as other fatty acids. Selective retention of trans fatty acids does not seem to occur; they are present in tissue in the same proportions that they are found in the diet. Trans fatty acids have been detected in adipose tissue, blood cells, serum lipoproteins, kidney, brain, heart, liver, aorta, jejunum, and human milk.

Desaturase and elongase enzymes are able to insert double bonds into and elongate trans fatty acids. However, the resulting elongated and desaturated trans fatty acids are not able to perform the same functions as if they were made from essential fatty acids.

If dietary essential fatty acids are low, trans fatty acids can impair the conversion of them into the raw material for eicosanoids. Remember that hydrogenation reduces the amount of essential fatty acids by converting them into trans fatty acids or saturated fatty acids. Since many people are low in one essential fatty acid (alpha-linolenic acid), this interference may be common. Meeting the recommended levels for alpha-linolenic acid and eliminating all trans fatty acids would prevent interference with the production of these vital eicosanoids.

Heart disease and trans fatty acids

The nurses health study (Hu, 1997) and others have shown us that the higher the dietary intake of trans and saturated fatty acids, the higher the risk of heart disease. We have also learned that the higher the intake of non-hydrogenated polyunsaturated fats, the lower the risk of heart disease. One study estimates that the replacement of 5 percent of energy from saturated fat with energy from unsaturated fats would reduce risk of heart disease by 42 percent (Hu, 1999). The replacement of only 2 percent of energy from trans fat with energy from unhydrogenated, unsaturated fats would reduce the risk of heart disease by 53 percent (Hu, 2009). Since average intakes of trans fatty acids are currently about 1-2 percent of calories, this indicates that heart disease could potentially be cut down dramatically if trans fatty acids were eliminated. Currently, it is not possible to determine whether there are differences between trans fatty acids from ruminant fat and trans fatty acids from hydrogenated vegetable oils in their effects on heart disease risk.

Trans fats and blood lipids

Trans fatty acids in diets have been found to raise both blood triglycerides and blood total cholesterol. Both of these factors raise the risk of coronary heart disease. Compared to a diet enriched with 10% oleic acid, a diet enriched with 10% trans fatty acid isomers of oleic acid raised blood cholesterol 28%. After-meal triglyceride levels were also raised (Gatto, 2003).

Both trans fatty acids and saturated fatty acids have been shown to raise LDL (bad) blood cholesterol. However, only trans fatty acids have been shown to lower blood levels of the beneficial HDL cholesterol. HDL cholesterol is needed to remove excess cholesterol to the liver where it can be excreted in bile. By increasing LDL while lowering HDL, trans fatty acids, gram for gram, increase the risk of heart disease even more than saturated fatty acids. We must remember that saturated fatty acids in typical diets are ten times higher than trans fatty acids. Thus, saturated fatty acids are still a more significant factor in heart disease risks.

Trans fatty acids do not seem to have any effects on other risk factors for cardiovascular problems. There have been no effects found on blood pressure. Trans fatty acids do not seem to change the oxidation of blood fats. Trans fatty acids have not been found to affect blood coagulation.

Diabetes and trans fatty acids

Dietary fatty acids are important in reducing the risk of type II diabetes. A higher intake of polyunsaturated fatty acids helps lower the risk of type II diabetes. A higher intake of trans fatty acids and saturated fatty acids increases the risk of type II diabetes by increasing insulin resistance. Trans fatty acids and saturated fatty acids also adversely affect glucose metabolism (Hu, 2001). In the Nurses Health Study a positive relationship was observed between the intake of trans fatty acids and the risk of development of type 2 diabetes.

Cell membranes are impacted by dietary choices of fatty acids. Polyunsaturated fatty acids result in a more flexible, fluid, and permeable cell membrane. Increased dietary intake of both trans fatty acids and saturated fatty acids results in cell membranes that are less flexible, fluid, and permeable. These less flexible cell membranes reduce insulin activity by altering the binding of insulin receptors (Pan, 1995). Ion permeability is reduced and cell signaling may be impaired.

Increased dietary fiber has been shown to reduce the risk of type II diabetes. Dairy products and beef account for a significant amount of trans fatty acid intake and have a very low content of dietary fiber. Baked products and margarine account for much of the dietary trans fatty acid intake and these products also have a very low content of dietary fiber. Lowering the dietary intake of trans fatty acids from both of these sources may result in increased fiber and lowered risk of type II diabetes.

Trans fatty acids in infants and children

Trans fatty acids from a mother's diet are found in the umbilical cord and the tissues of her growing infant. These dietary trans fatty acids are also found in mother's milk. These trans fatty acids are not produced by the mother, but passed along from dietary sources. With more trans fatty acids in the fetus or infant, lower levels of essential fatty acids and their long-chain derivatives have been found.

In childhood, a positive relationship was observed between the prevalence of asthma, allergic inflammation of the eyes and nose, and atopic eczema with the intake of trans fatty acids (Weiland, 1999). Research is ongoing and no mechanism has yet been established.

Trans fatty acids from dairy products and beef

Between 21% and 60% of dietary trans fats come from ruminant products such as dairy products, beef, and mutton. These ruminant trans fatty acids make up about 3-6% of the fat in milk and beef. In the United states the amount of dietary trans fatty acids from ruminant sources was about 21% in 1995. In Australia, 60% of the trans fatty acids came from ruminant sources in 2007. In New Zealand 41% of the trans fatty acids came from ruminant sources in 2007. In Canada 19% of the trans fatty acids came from ruminant sources in 2006. In Denmark, 50% of the trans fatty acids came from ruminant sources in 2004 (Skeaff, 2009). As time goes on, the proportion of ruminant trans fatty acids to industrially produced trans fatty acids is going up. Voluntary industry cooperation, consumer choices, and government restrictions are reducing the amount of industrially produced trans fatty acids in diets worldwide. The dietary intake of ruminant trans fatty acids, however, is steady.

The trans fatty acids from ruminant products have not been proven to be less hazardous that other trans fatty acids. As a recent British update on the relation of trans fatty acids to health stated, "There are also inadequate data to demonstrate that trans FA [fatty acids] from different dietary sources have differential effects on CHD [coronary heart disease] risk or lipoprotein profiles." (Jackson, 2007).

A significant proportion of the total trans fatty acids, from 21% to 60%, is due to trans fatty acids from ruminant products. If we eliminate just the trans fatty acids resulting from industrial hydrogenation, we can cut down trans fatty acid intake by 40-79%. If we eliminate trans fats from both ruminant products and hydrogenation, we can eliminate trans fatty acid intake entirely. This would result in a decrease in heart disease estimated at 53%. The reduction in saturated fatty acid intake from eliminating ruminant products would be even more significant in reducing heart disease. With over one million serious heart attacks yearly in America alone, a reduction would be welcome.

The point has been made that if we eliminate dairy products, mutton, and beef, we would be undernourished. These products do contain calcium, protein, zinc, and other important nutrients. If we were to stop eating these ruminant products without replacing them with other nutritious food, then nutritional deficiencies could develop. If our goal is to reduce heart disease, then these foods should be eliminated and replaced with other sources of calcium, protein, zinc, and other nutrients. The substitution of other foods is well understood and does not present any difficulties aside from food preferences and habit patterns. The elimination of beef, mutton, and dairy products would also have a significant lowering effect on saturated fatty acid intakes, further reducing heart disease. On a political and economic level, the beef and dairy industries are powerful lobbyists and advertisers. A choice must be made between the profits of these industries and decreased heart disease.

Structure of trans fatty acids

Trans-fatty acids are most commonly made from the monounsaturated oleic acid. Trans isomers of oleic acid make up about 65% of all trans fatty acids in average diets. Either of the essential fatty acids, linoleic acid (LA) or alpha-linolenic acid (ALA), can also be made into a trans fatty acid. Trans isomers of the essential fatty acids make up about 12% of trans fatty acids in average diets. Palmitoleic acid (16:1 n-7) can also be converted to its trans form, Palmitelaidic acid (16:1 n-7t). A small amount of other fatty acids are converted to their trans isomers.

Any fatty acid with one or more double bonds has the capacity to be altered into a trans configuration. A fatty acid that is already saturated has no capacity to become a trans isomer. Trans fatty acids have at least one double bond in the trans configuration; they also sometimes have one or more normal cis bonds.

An isomer is one of two molecules sharing the same chemical formula, but with different physical shapes. Two different isomers often have different chemical and biological properties. A cis isomer of a fatty acid has the two hydrogen atoms on the same side of the carbon chain. Cis means "on the same side" in Latin. A trans isomer of a fatty acid has the two hydrogen atoms on opposite sides of the carbon chain. Trans means "across" in Latin.

Figure 60 Structural difference between natural and trans fatty acids

The location of the trans and cis double bonds is sometimes counted from the delta (Δ) end of the fatty acid. The trans-alpha-linolenic acid shown above is termed "cis 9, trans 12, cis 15 18:3 n-3." This exact terminology is needed because the trans double bond(s) can be at any double bond in the fatty acid.

Remember that the delta numbers are counted from the opposite end of a fatty acid than the omega numbers. This can cause confusion between the omega and delta numbers. The first double bond in the 18-carbon trans-alpha-linolenic acid is at omega-3, which is also called delta-15. It would be nice if we could always count from the same end of a fatty acid, but biochemists switch between counting from either the omega or the delta end. With trans fatty acids, the delta numbers are often used.

Figure 61 Structure of trans oleic acid and vaccenic acid

Trans isomers of oleic acid contributed the majority (somewhere between 54 and 82 percent) of the total trans fatty acids in diets. In the figure above we can see two different trans isomers of oleic acid. These are the two most common forms of trans fatty acids. Elaidic acid (shown above) is the most common trans fatty acid found in hydrogenated oils. Vaccenic acid (shown above) is a positional isomer as well as being a trans isomer. Positional isomers have the double bond shifted to another position along the fatty acid. In this case, vaccenic acid has had its double bond shifted to omega-7 from omega-9. Vaccenic acid is the most abundant trans fatty acid in milk fat and other ruminant products. Vaccenic acid can be altered by delta-9 desaturase to become conjugated linoleic acid. Added together, vaccenic acid and elaidic acid make up 48% of the trans fatty acids in dairy fat and 40% of the trans fatty acids in hydrogenated oils.

Natural double bonds (called "cis") have the two hydrogen atoms on the same side of the fatty acid, as shown above. The cis-fatty acids are bent at the double bond, which lowers their melting temperature, as shown below. Cis-fatty acids pack together loosely. Trans isomers have the two hydrogens of the double bond on opposite sides. Trans-fatty acids are straight at the trans double bond. Trans-fatty acids have a higher melting temperature and they pack more tightly together.

Figure 62 3-D structure of trans-oleic, oleic, and stearic acids with melting points

In nature, most double bonds are in the cis configuration. The only natural exception is found when bacteria in the rumen of certain animals create trans-fatty acids. This is how trans-fatty acids occur in dairy products and beef. Trans-fatty acids are also commonly formed as an unwanted byproduct during the hydrogenation of oils.

Trans fatty acids in animal vs. vegetable fats

Trans Isomer	Delta Position	% From Milk Fat	% From Hydrogenation
18:1 n-2	16	9	1
18:1 n-3	15	5	2
18:1 n-4 (and n-5)	14, 13	15	11
18:1 n-6	12	8	11
18:1 n-7 (vaccenic acid)	11	40	15
18:1 n-8	10	10	15
18:1 n-9 (elaidic acid)	9	8	25
18:1 n-10 (and n-11, n-12)	8, 7, 6	6	16
18:2 isomers (linolaidic acid)	any	1	3

Figure 63 Chart of trans isomers in milk fat and from hydrogenation

As you can see from the chart above, all of the various common trans fatty acids are found in both milk fat and hydrogenated fat. The amounts vary between the two sources of trans fatty acids. This chart uses averages of the trans fatty acids found in hydrogenated oils, but variations are common. The amounts of trans fatty acids in ruminant products such as milk fat also vary. As you can see, vaccenic acid is found in higher amounts in milk fat, while elaidic acid is found in higher amounts in hydrogenated fat.

Proportions of the various trans fatty acids in milk fat are similar to the amounts in beef, goat meat, mutton, goat milk, and sheep's milk. There are wide variations in the exact amount of each trans fatty acid in all of these products. Hydrogenated oils also have a wide variation of the content of their various trans fatty acids.

Conjugated linoleic acid

Conjugated linoleic acid (CLA) can be made from linoleic acid by bacteria in the rumen of cows, goats, or sheep. It is also known a alpha-rumenic acid. It is not present in trans fatty acids from hydrogenation. Conjugated linoleic acid is a family of at least 13 isomers of the essential fatty acid linoleic acid. It is found in small amounts in dairy products and beef, about one-half to two percent of the fat. In Europe the daily intake of conjugated linoleic acid is estimated at 300 milligrams. In the United States, intake is slightly lower at 150-200 milligrams per day. In Australia intake can be 1500 milligrams per day. Conjugated linoleic acid can be biosynthesized in the body from vaccenic acid, another trans fatty acid found in ruminant products.

Dairy products are the main source, providing about 60% of conjugated linoleic acid. Beef supplies most of the rest with 32% of dietary intake. Pork, poultry, and other foods provide only 2-3% of dietary conjugated linoleic acid each. Studies on the health effects of these small amounts of dietary conjugated linoleic acid do not clearly agree on any good or bad effects on health.

Conjugated linoleic acid is a trans fatty acid. There are two main differences between the essential fatty acid linoleic acid and conjugated linoleic acid. The bonds are closer together in conjugated linoleic acid and at least one of the bonds is a trans bond.

Figure 64 Structure of a conjugated fatty acid

Regular linoleic acid has two double bonds along the carbon chain of the fatty acid (see the above figure). These are at omega-6 and omega-9. The vast majority of natural fatty acids have the double bonds separated by two carbon atoms. However, conjugated linoleic acid has its double bonds separated by only one carbon atom, in the case above, at omega-7 and omega-9.

This conjugated form of linoleic acid is no longer an omega-6. When desaturated and elongated into trans isomers of arachidonic acid and eicosanoids, it will not have the natural configuration and will not act the same biologically. Also, conjugated linoleic acid may inhibit delta-6 and delta-5 desaturation of the essential fatty acids. In other words, conjugated fatty acids interfere with the essential fatty acids and their elongation and desaturation into eicosanoids.

Trans fatty acid double bonds are counted from the delta end of the fatty acid. The one above has double bonds at delta-9 and delta-11. This form of conjugated linoleic acid makes up from 70-90% of the conjugated linoleic acids found, mostly in beef and dairy products.

Conjugated linoleic acid also has at least one trans bond. This classifies it as a trans fatty acid. Trans bonds tend to make the fatty acid straighter, changing the shape of phospholipids in cell membranes. This straightness can, for instance, inhibit the movement of glucose into the cells by reducing the binding of insulin receptors. This can increase the risk of diabetes. Normal cis bonds make the fatty acid bend, so they pack together more loosely, with more insulin receptors.

Dietary amounts of conjugated linoleic acid have effects on sugar metabolism that are hard to detect. However, supplements with 10 times or more than the dietary levels of conjugated linoleic acid have been shown to decrease insulin sensitivity in overweight people. Decreased insulin sensitivity is the major symptom of type II diabetes.

Studies in lab animals have shown weight loss with high amounts of conjugated linoleic acid. There is some evidence of adverse effects on lipid and glucose metabolism and on insulin sensitivity of supplemental CLA in humans (Maloney, 2004). Results are inconsistent and effects may differ between the CLA-isomers. There are many isomers and they seem to have different or opposing effects. Conjugated linoleic acid supplementation was found to increase oxidative stress and inflammatory biomarkers in obese men (Risérus, 2002).

Higher amounts of conjugated linoleic acid were correlated with lower infant birth weight. There was also a negative effect on gestation length (Elias, 2001).

Conjugated linoleic acid is not a necessary or desirable component of a healthy diet. Supplementary conjugated linoleic acid may have potential dangers and should not be seen as a safe alternative to healthful diets and increased activity for losing weight.

References:

(Elias, 2001) Elias SL and Innis SM, "Infant plasma trans, n-6, and n-3 fatty acids and conjugated linoleic acids are related to maternal plasma fatty acids, length of gestation, and birth weight and length," (2001) Am J Clin Nutr 73: 807-814.

(Gatto, 2003) Lissa M. Gatto, David R. Sullivan, and Samir Samman, "Postprandial effects of dietary trans fatty acids on apolipoprotein(a) and cholesteryl ester transfer," Am J Clin Nutr 2003;77:1119–24.

(Jackson, 2007) Alan Jackson, Chair, Scientific Advisory Committee on Nutrition, "Position statement by the Scientific Advisory Committee on Nutrition," British Food Standards Agency, 2007.

(Katan, 2006) M. B. Katan, "Regulation of trans fats: the gap, the polder, and McDonald’s French fries," (2006) Atheroscler Suppl 7, 63–66.

(Hu, 2009) Frank B. Hu, Meir J. Stampfer, Joanne Manson, Eric Rimm, Graham A. Colditz, Bernard A. Rosner, Charles H. Hennekens, and Walter C. Willett, "Dietary fat intake and the risk of coronary heart disease in women," 2009, NEJM, Volume 337, Number 21, 1491.

(Hu, 2001) Frank B. Hu, R.M. van Dame, S. Liu, "Diet and risk of Type II diabetes: the role of types of fat and carbohydrate," Diabetologia (2001) 44: 805-817.

(Hu, 1999) Frank B Hu, Meir J Stampfer, JoAnn E Manson, Alberto Ascherio, Graham A Colditz, Frank E Speizer, Charles H Hennekens and Walter C Willett, "Dietary saturated fats and their food sources in relation to the risk of coronary heart disease in women," American Journal of Clinical Nutrition, Vol. 70, No. 6, 1001-1008, December 1999.

(Hu, 1997) Frank B. Hu, Meir J. Stampfer, Jo Anne Manson, Eric Rimm, Graham A. Colditz,

"Dietary fat intake and the risk of coronary heart disease in women," New England Journal of Medicine 1997 Volume 337 Number 21.

(Moloney, 2004) Moloney F, Yeow TP, Mullen A, Nolan JJ, Roche HM. "Conjugated linoleic acid supplementation, insulin sensitivity, and lipoprotein metabolism in patients with type 2 diabetes mellitus," Am J Clin Nutr. 2004;80:887–895.

(Pan, 1995) Pan DA, Lillioja S, Milner MR et al. "Skeletal muscle membrane lipid composition is related to adiposity and insulin action." 1995 J Clin Invest 96: 2802-2808.

(Risérus, 2002) Ulf Risérus, MMed; Samar Basu, PhD; Stefan Jovinge, MD, PhD; Gunilla Nordin Fredrikson, PhD; Johan Ärnlöv, MD; Bengt Vessby, MD, PhD, "Supplementation With Conjugated Linoleic Acid Causes Isomer-Dependent Oxidative Stress and Elevated C-Reactive Protein A Potential Link to Fatty Acid-Induced Insulin Resistance," Circulation. 2002;106:1925.

(Skeaff, 2009) C.M. Skeff, "Feasibility of recommending certain replacement or alternative fats," European Journal of Clinical Nutrition (2009) 63, S34–S49.

(Stender, 2006) S. Stender, J. Dyerberg, A. Astrup, "High levels of industrially produced trans fat in popular fast foods," (2006) N Engl J Med 354, 1650–1652. And S. Stender, J. Dyerberg, A. Bysted, A. Astrup, "A trans world journey," (2006). Atheroscler Suppl 7, 47–52.

(Weiland, 1999) Weiland SK, von Mutius E, Hüsing A, Asher MI, on behalf of the ISAAC Steering Committee, "Intake of trans fatty acids and prevalence of childhood asthma and allergies in Europe," (1999) Lancet 353: 2040-2041.

Part III: Best Oils, Worst Fats

Chapter 8: Comparing fats and oils

Summary

We know that the healthiest oils are still inside food. These haven't been crushed out of the seed, exposed to oxygen, ruined with light, heated, bleached, and robbed of their antioxidants. Yet massive quantities of liquid and solid oils are used for salad dressing, cooking, on toast, and many other uses. It is healthiest to avoid extracted oils as much as possible.

Solid fats are less healthy than liquid oils. They have the least amount of vitamin E and the least amount of the essential fatty acids. Solid fats have either too much of the saturated fats or too much of the trans fats or both. Solid fats such as coconut oil are useful for high heat cooking because they resist rancidity.

The best oils have a generous amount of vitamin E, are low in saturated fats, have no trans fats, and have a good proportion of the essential fatty acid alpha-linolenic acid. Unrefined soybean, canola, olive, and sesame oils are some of the healthiest oils on the market. When refined, they lose much of their vitamin E, are reduced in essential fatty acids, acquire some trans fats, and acquire oxidation products. Additionally, the best oils are organically grown and processed to avoid residues of pesticides and the refining solvent hexane.

What makes an oil or fat healthy?

This chapter will show you which are the healthiest oils in common use so you can make an informed decision. The next chapter will compare some of the less common oils. Please remember just one abbreviation: ALA for alpha-linolenic acid, the hard-to-get essential fatty acid.

A nice balance of the essential fatty acids

The best oils have a nice balance of the two essential fatty acids, linoleic acid and alpha-linolenic acid (ALA). It is best if the linoleic acid consumed in a day is less than 10 times the ALA consumed in that day. Ideally, the ratio of linoleic acid to ALA should be in the range of 2 to 1 up to 4 to 1. Only a few oils such as canola oil, and soybean oil have adequate amounts of ALA and a fairly nice balance of these two essential fats. Other oils may have a nice balance, but they contain insignificant amounts of ALA.

Flax seeds, along with perilla and chia seeds, have more ALA than linoleic acid. The powder or oil from these three seeds can restore the balance of the essential fatty acids to a diet too high in linoleic acid.

Oils need the protection of vitamin E

Oils need protection before and after we eat them. The best oils have a high content of vitamin E, our most powerful fat-soluble antioxidant. Any oil with low amounts of vitamin E will be less able to quench free radicals in our arteries. Vitamin E in food is important because it prevents the arterial damage that can result in heart attacks and strokes. Another antioxidant, beta-carotene, is the commonest form of vitamin A in diets around the world. The few oils that are unprocessed enough to have any remaining beta-carotene are healthier. The rich red color of unprocessed palm oil is due to high amounts of beta-carotene.

Avoid trans fats

What makes an oil unhealthy? Trans fats are one of the least healthy fatty acids. Watch out for oils that are partially hydrogenated, because these contain trans fats. Soybean and cottonseed oils are commonly sold partially hydrogenated. Many other oils can be hydrogenated as well. Trans fats are also found in butter and lard. The trans fats in butter and lard, along with the high levels of saturated fats, increase the potential for arterial clogging.

Figure 65 Graph of saturated fats in common oils

Saturated fats

Certain saturated fatty acids have been proven to increase our risk of heart attacks and strokes. A high content of palmitic acid, myristic acid, or lauric acid makes any oil unhealthy The graph above shows the content of total saturated fats and also the content of the artery-clogging saturated fats. You may note that the tropical oils and the animal fats are highest in both categories of saturated fats.

It is best to keep your saturated fats below 20 grams, or about one tablespoon in any day. You can't get too little of the saturated fats because your body will make saturated fats if you need them.

Another fatty acid, oleic acid is found in many oils. Oleic acid is healthy, and it can take the place of dietary saturated fats, thus improving the diet. Oleic acid is monounsaturated. Oleic acid is the most stable of the unsaturated fatty acids. This makes oils high in oleic acid more suitable for low and moderate heat cooking.

Organic oils are healthier

Oils contaminated with toxins such as pesticides or cancer-causing chemicals are less desirable than organic oils. Organic oils are also preferable as they have no residues of hexane, a solvent used to increase the oil yield of many beans and seeds. Many people choose to avoid oils that have been genetically engineered. Organic oils are not allowed to be genetically engineered.

Processing can ruin a good oil

Another way to gauge the healthiness of oils is to look at how they have been processed. The best oils are cold pressed. Oils that are expeller pressed without solvents are also a healthier choice. Heavily processed oils are less healthy. They are heated, bleached, deodorized, and lower in natural antioxidants. The vast majority of oils on the market are heavily processed.

Comparing fats and oils

Let's take a look at the most popular fats and oils to see how healthy they are. We can also take a look at their flavor and cooking properties. We will use a serving size of two tablespoons of each oil for comparison purposes.

Butter

Butter is a widely used around the world because of its unique flavor and cooking properties. Butter is useful for frying because the saturated fats in butter are resistant to heat. Two tablespoons are laden with 9 grams of saturated fat; this is about half of the daily recommended upper limit for saturated fats because of the risk of heart attacks. Butter also contains short chain saturated fats that, like carbohydrates, are burned for energy, and these do not raise blood cholesterol. About one fifth of the oil in butter is healthy oleic acid. There are insignificant amounts of the two essential fats. We would need an unrealistic 20 servings of butter to get enough of the essential fats for one day. Although butter is the dairy product with the highest amount of vitamin E, one serving still has only three percent of our minimum daily need for this vital antioxidant.

People who eat butter would be well-advised to select organic butter over commercial butter for several reasons. Some commercial butter has been shown to contain toxic cancer-causing organic pollutants, which can exceed maximum levels (Loutfya, 2007). Commercial butter can contain five to 20 times the amount of pesticide residues that vegetable oils contain (Kalantzi, 2001). Commercial butter can contain residues of the antibiotics used on dairy cows. This can cause antibiotic resistant bacteria to grow in people who eat this butter. About 80% of the dairy cows in the United States are being given a genetically modified growth hormone that may result in higher rates of breast and prostate cancer in the people who consume these dairy products (Epstein, 2001). Even organic butter often contains small amounts of trans fatty acids that may take the place of essential fats in cell membranes. Many of these contamination issues with butter are at a lower level or are nonexistent in vegetable oils.

Canola oil

Canola oil is mild tasting. Unhydrogenated canola oil is not suitable for hot frying and is best used for salad dressing and other unheated applications. The relatively high content of delicate essential fatty acids can become rancid with excessive heat.

Canola is not a natural oil, but it is a very good oil from a nutritional standpoint. Canola oil was produced by exposing rapeseeds to a mutagenic chemical and choosing the seeds with the best nutritional profile. As we shall see, canola is not the only oil to be selectively mutated in this way.

Canola oil, like many other oils, is often pressed after a solvent is added to the crushed seeds. One common solvent is hexane, which is toxic to nerves. The healthiest canola oil is organic and cold pressed without solvents. Some canola oil is partially hydrogenated and contains trans fats. There is also a canola oil available that has been genetically altered to have less of the essential fatty acid ALA. This may be good for shelf life or cooking properties, but you lose the benefits of the naturally high levels of ALA.

Canola oil contains very low levels of saturated fat. Of the dangerous saturated fats, canola oil contains just one percent. Canola oil is made up of almost two thirds (62%) healthy oleic acid. In addition, just two tablespoons will give you enough ALA for a whole day. Canola oil also contains some of the other essential fatty acid, linoleic acid. Two tablespoons supply about one quarter of a day's need for linoleic acid. Since there is only twice as much linoleic acid as ALA, canola oil helps you balance the two essential fats. There is more good news. Canola oil is high in vitamin E. Two tablespoons provides one third of the minimum daily need for vitamin E.

Figure 66 Graph of ALA in common oils with ratios of LA/ALA

We need about two grams of the essential fat ALA in a day. Those oils with little ALA and a high ratio of linoleic acid to ALA increase the risk of inflammation and arterial disease.

Cocoa butter

Cocoa butter is made from the seeds of Theobroma cacao; these are the same seeds that are processed into chocolate. Cocoa butter is very rich and creamy. It is hard at room temperature, but melts quickly on the skin. It has the delicate aroma of chocolate. It is often mixed into the more expensive chocolate bars for a smooth texture.

Cocoa butter contains little of the essential fats. It would take over 20 servings to make up one day's intake of linoleic acid. It contains no ALA at all. One third of the oils in cocoa butter are in the form of healthy oleic acid. Although cocoa butter contains saturated fats, it is not usually eaten in large enough quantities to influence blood cholesterol. Vitamin E levels are very low, with only about three percent of the minimum daily intake in one serving. Cocoa butter is eaten for the smooth texture it lends to food, not for its nutrition. The healthiest cocoa butter is made from organic cacao. This is because commercial cacao is normally heavily sprayed with pesticides.

Figure 67 Balancing the essential fatty acids in cooking oils

Text Box: Balancing the essential fatty acids in cooking oils
Only flax, perilla, and chia seeds have more ALA than linoleic acid
Canola and soybean oil have enough ALA and not too much linoleic acid
Vegetable shortening, butter, corn oil, and lard have tiny amounts of ALA
Most other cooking oils have very little ALA
Cottonseed, sesame, sunflower, and safflower oils lack ALA and have too much linoleic acid

Coconut oil

Coconut oil is made from the dried meat of mature coconuts. Coconut oil is quite hard at room temperature. This solidity makes it ideal for baked goods and candy. Coconut margarine may be free of trans fat, but the amount of artery-clogging saturated fats is just too high to be healthy. Coconut oil has a coconut aroma and feels thick and persistent on the skin. Coconut oil is perfect for cooking at high temperatures without becoming rancid.

Coconut oil contains the most saturated fat of any fat or oil, with almost all of the oil being saturated. Two tablespoons contain the maximum amount of saturated fats recommended for a single day. Coconut oil contains a very low amount of healthy oleic acid. The content of essential fats is also very low. There is no ALA and only a trace of linoleic acid. Vitamin E is almost totally absent from coconut oil.

Palm kernel oil is very similar in composition to coconut oil, with similar amounts of lauric acid, saturated fats, essential fats, and vitamin E. You can think of the palm kernels as little coconuts.

The short and medium chain fatty acids in coconut oil are able to kill certain bacteria and viruses. Lauric acid, a 12-carbon fatty acid can be digested into monolaurin. Monolaurin can exert its effect on the lining of the stomach and also on the skin when applied topically. Studies have also shown that monolaurin is effective in killing a common intestinal parasite, Giardia lamblia.

Capric acid is a medium chain saturated fatty acid with 10 carbon atoms. It is found in coconut oil as six percent of the fats. Capric acid can also have antimicrobial properties. Capric acid can be digested into monocaprin, which is effective in killing certain flu viruses. Monocaprin can be added to juices to kill germs. Both monolaurin and monocaprin are effective in killing certain strains of streptococcus and also E. coli bacteria. During absorption from the intestines, both monocaprin and monolaurin are made into triglycerides and lose their antimicrobial properties. These fats are important for killing certain bacteria and viruses in the intestines and on the skin, but are transformed into triglycerides before entering the bloodstream.

Figure 68 Graph of vitamin E in common oils

Corn oil

There is not much oil in corn. Only five percent of a corn kernel is oil. Corn oil has a mild taste and is a light yellow in color. Corn oil has been used as a food oil only for a short time—since industrial processes created it in the 1930s. Corn oil is used in salad dressings, and when partially hydrogenated, it is made into margarine. It is widely used as a cooking oil.

Corn oil contains a very small amount of saturated fat. It contains a generous amount of linoleic acid. One serving provides about three-quarters of a daily need for this essential fatty acid. The content of ALA is small, but a serving does provide about one-sixth of the daily need for this essential fatty acid. Corn oil has 50 times as much linoleic acid as it does ALA. This is unbalancing and increases tendencies towards inflammation. It contains about one quarter healthy oleic acid. Vitamin E content is good. One serving contributes about one quarter of the minimum daily need for this important antioxidant.

Cottonseed oil

Cotton is a non-food crop with many pest problems and is heavily sprayed. The oil is a byproduct of cotton production. Cottonseed oil production in the United States ranks third after soybean oil and corn oil. The flavor is mild and it is a stable oil during storage. It is also a stable frying oil.

Solvents are often used in commercial production, so contamination with hexane is possible. About one quarter of the fat is saturated, which is a high amount of saturation for a vegetable oil (the highest). This makes it desirable by manufacturers of crackers, candy, and cookies. Cottonseed oil is often partially hydrogenated, which makes it even better for making crispy potato chips.

Cottonseed oil is rich in linoleic acid. One serving supplies three quarters of the daily need for this essential acid. It has only a little of the other essential fatty acid. It would take 20 servings to get enough ALA for one day. Cottonseed oil has 144 times as much linoleic acid as it does ALA. Since the healthiest ratio is four to one, this oil is unbalancing to the essential fats. Oleic acid content is a bit low at 17%. Vitamin E content is surprisingly high. One serving supplies two thirds of the minimum daily need for vitamin E.

Flax oil

Flaxseed oil is mainly used as a health supplement, rather than as a cooking oil. It has a rich golden color and a grassy smell. It must be handled very carefully as it is one of the most fragile oils. Its fragility is due to the very high content of ALA. It is best not to heat it, but to add it after cooking or in a salad dressing. Proper pressing must be under cool conditions and the oil is best preserved in nitrogen gas in a dark bottle. You can keep it in the refrigerator; even so, it should have an expiration date.

Flaxseed oil contains only a trace of saturated fats. However, it is a gold mine of ALA. Just two tablespoons contain a whole week's worth of ALA. This is the rare oil that can reestablish the balance between the essential fatty acids. Flaxseed oil does contain some linoleic acid. One serving supplies about one-sixth of the daily need. With a ratio of one part linoleic acid to four parts ALA, it is an important source of that hard-to-get ALA. This oil also contains one-fifth of the healthy oleic acid. Flaxseed oil has a generous amount of vitamin E. One serving supplies about one-third of the daily minimum for vitamin E.

Lard

Lard is made from pig fat. It is still used in some potato chips and pastries. It can be solid or soft at room temperature. It is made up of about one-third saturated fats. One serving of two tablespoons has over half of the daily maximum amount of saturated fats. Most of these saturated fats are the ones that increase the risk of heart attacks and strokes. One serving of lard has only one-sixth of the daily need for the two essential fats. The ten to one ratio of linoleic acid to ALA is not important since there is such a low quantity of essential fats. Lard contains about one-third of the healthy oleic acid. The vitamin E content is very close to zero. Contamination of lard can include pesticides, antibiotics, growth hormones, and, if not cooked well, bacteria.

Olive oil

Olive oil is a much-loved oil in the Mediterranean area. The olives are crushed and pressed to produce extra virgin olive oil. This first pressing results in an oil that has the rich green color of chlorophyll and beta-carotene. Virgin olive oil is not normally heated, deodorized, hydrogenated, bleached, or stripped of lecithin. Olive oil retains a trace of iron and calcium. It also has natural antioxidants. The best olive oil is extra virgin and found in dark bottles or cans. Olive oil should be used raw or for light sautéing. Olive oil is too fragile to be used for high heat frying.

Olive oil is quite low in saturated fat. It would take five servings to reach the daily maximum for saturated fats. Olive oil contains some essential fats, but is not rich in them. It would take about ten servings to get enough of the essential fats, but this would be too much oil. Olive oil has about 14 times as much linoleic acid as ALA, so the ratio is not too far away from the ideal balance. Oleic acid was named for olive oil, so it is not surprising that olive oil is very high in oleic acid, about 70%. Olive oil is a good source of vitamin E. Four servings supply the minimum daily need for vitamin E. Virgin olive oil may be one of the least contaminated of the oils because solvents are not used during processing. Olives have not been genetically engineered or mutagenically altered.

Palm oil

Palm oil is the largest crop in the world of any edible oil. Part of the palm oil in production is now being turned into biodiesel. Unrefined palm oil has been used for cooking for centuries. The unrefined oil is a deep red or orange in color. The color comes from the high beta-carotene content. Boiled palm oil has a white color and is devoid of much of the original beta-carotene. This oil is rarely seen in a bottle on a shelf in America. It is found in many baked goods. It is also found in some margarines, mainly in Europe. It is used as a frying oil in many areas of the world.

About half of the oil in palm oil is saturated. Palmitic acid was named after this heavily saturated oil. It only takes one and a half servings of palm oil to reach the daily maximum of artery-clogging saturated fats. Palm oil is very low in essential fats. Only one-twentieth of the daily need for these essential fats is satisfied with a serving. Palm oil contains about 36% oleic acid. Palm oil is rich in vitamin E with one-third of the daily minimum of this antioxidant in every two-tablespoon serving.

Figure 69 Which is the best oil?

Text Box: Which is the best oil?
Canola oil contains very low amounts of saturated fats, high amounts of ALA, and high amounts of vitamin E. Canola oil also has a nice two-to-one ratio of linoleic acid to ALA.
Coconut oil is best for high heat frying.
Sesame oil is best for medium heat frying.
Flax oil is great for rebalancing the linoleic/ALA ratio. Flax oil contains high amounts of vitamin E and very low amounts of saturated fats. It must be kept cool.
Olive oil contains a moderate amount of vitamin E. This oil contains only small amounts of ALA and the ratio of linoleic acid to ALA is a bit high at 14 to one. It is low in saturated fats. Extra virgin olive oil is unusual in being cold pressed without solvents. Residues of beta-carotene, chlorophyll, and iron remain in this oil.
Soybean oil contains moderate amounts of vitamin E and low, but significant amounts of ALA. It is low in saturated fats. Unrefined, cold-pressed soybean oil is a healthy oil rich in lecithin.

Peanut oil

Peanut oil is considered a premium oil for cooking and frying because of its nice flavor. It is a bit more expensive that other cooking oils. Peanut oil resists rancidity, partly because of its very long-chain saturated fatty acids. Peanut oil is routinely extracted using a chemical solvent such as hexane. Americans get much of their peanut oil from eating peanut butter. Peanut butter is high in oil; about fifty percent of peanut butter is peanut oil. Some peanut butter contains hydrogenated oil.

Peanut oil contains very little saturated fat. One serving supplies almost half of the essential linoleic acid. It has virtually no ALA. Peanut oil is made up of almost half of the healthy oleic acid (45%). Peanut oil is rich in vitamin E with each serving containing almost one-third of the daily need for this vital antioxidant.

Safflower oil

Safflower oil is a light yellow in color and has a mild flavor. It is made from seeds that resemble sunflower seeds, but are smaller in size. There are two varieties available. The original safflower oil is very high in linoleic acid. In the 1970s, the seeds were selectively mutated to produce a more stable high oleic variety. Expeller-pressed safflower oil is free of solvent residues that may be found in the solvent-extracted oil.

Both types of safflower oil are deficient in the essential fatty acid ALA. The high oleic variety contains three-quarters oleic acid and 14% linoleic acid. The original safflower oil is just the opposite with three-quarters linoleic acid and 14% oleic acid. The high oleic variety is considered healthier because it does not overbalance the ALA in the diet with excess linoleic acid. The high oleic variety is more suitable for frying with its low content of fragile linoleic acid. Safflower oil is very low in saturated fats, being only four percent saturated. The vitamin E content is very high with one serving providing three-quarters of the minimum daily requirement.

Sesame oil

Cold-pressed unrefined sesame oil is dark in color and has a distinctive flavor. It is used in Asian cooking. Refined, solvent-extracted sesame oil is also available. This sesame oil is light in color and has a mild flavor. Sesame tahini is a creamy paste made from crushed sesame seeds. Sesame tahini is rich in calcium. Sesame oil is useful for medium heat cooking. It contains antioxidants including sesamin that are heat-activated.

Sesame oil is low in saturated fats and even lower in the cholesterol-raising palmitic acid. Sesame oil is largely made up of the essential fat linoleic acid and the healthy oleic acid. The ALA content is quite low with a serving providing only one-twentieth of the daily need. The ratio of linoleic acid to ALA is 116, so sesame oil has an unbalancing effect on the essential fats. Sesame oil is very low in vitamin E; it would take 37 servings to make up even the minimum amount of vitamin E for one day.

Soybean oil

Soybeans are a major worldwide crop for food, for oil, for protein isolates, and for animal feed. Most of the oil used in the United States is soybean oil. After the soybeans are ground and crushed, a solvent such as hexane is normally used. Expeller pressed soybean oil without solvent residues may be available in health food stores. Soybean oil is often partially hydrogenated to keep the delicate ALA from degrading and ruining the flavor. Hydrogenated soybean oil is commonly used to fry French fries and doughnuts.

Soybean oil contains only a small amount of saturated fats. One serving has just a fifth of the healthy limit for one day's saturated fat. About half of the oil is in the form of linoleic acid. Soybean oil is a good source of ALA as well. One serving provides enough ALA for the whole day. The ratio of linoleic acid to ALA is seven to 1. This is a good ratio for these two essential fats. These essential fats are much lower in partially hydrogenated soybean oil since they have been converted to saturated fats or trans fats.

Soybean oil contains about one-quarter of the healthy oleic acid. Vitamin E is somewhat low in soybean oil. Each serving has only one-seventh of the vitamin E needed for one day.

Sunflower oil

Sunflower seed oil comes in two varieties. Natural sunflower oil is rich in linoleic acid. Selective breeding using mutation has resulted in a variety of sunflower oil that is very rich in oleic acid. This oil is more stable in storage and when used for frying. Both varieties are light in color and mild in flavor. After hulling, the seeds are crushed and a solvent such as hexane is used to extract all of the oil. The oil normally undergoes degumming, bleaching, wax removal, and deodorization.

Sunflower seed oil has very low levels of saturated fats. The natural, high-linoleic oil has almost enough linoleic acid for a whole day in just one serving. The high-oleic variety has just a small amount of linoleic acid. The high-oleic variety is aptly named with over three-quarters of the oil as oleic acid. The normal variety contains one fifth oleic acid. Neither variety contains much of the essential ALA. Vitamin E levels are the highest of any oil with one serving providing almost the minimum amount for a whole day.

Figure 70 Graph of oleic acid in common oils

Vegetable shortening

There are many different formulations of vegetable shortenings on the market. The one used in this example is a common one: partially hydrogenated soybean oil mixed with partially hydrogenated cottonseed oil. The big problem with this vegetable shortening is that it contains about 21% trans fats. If the manufacturer selects the serving size of 2 grams, then the product can be labeled as "trans fat free." However, a more realistic serving of two tablespoons contains about 6 grams of trans fats.

It also contains about one quarter saturated fats. Both the trans fats and the saturated fats have been increased by hydrogenation. Although they are very unhealthy, they give baked goodies that perfect texture. Alternate formulations may be made from tropical oils, which are more saturated, but may not contain trans fats.

Vegetable shortening has enough linoleic acid so that three servings supply a day's need. There is enough ALA so that five servings supply one day's worth of this essential fat. Almost one-half of the oil in this shortening is healthy oleic acid. There is an insignificant amount of vitamin E. It would take an unrealistic 68 servings to supply the minimum amount of vitamin E for one day.

Genetic alteration of oil seeds

The oil industry wants seeds that grow productive, disease-resistant crops. Oil seeds are often changed to increase the profit derived from growing them. These oil seeds are also often changed to alter the types of fatty acids in the seeds. Sometimes oil crops have toxins that can be removed with genetic modification.

Mutagenic breeding

Historically, crops have been bred selectively by choosing seeds from the best plants. In modern times, more powerful methods are used. One example is canola. Scientists altered rape seeds to have much less of a toxic compound, erucic acid. Canola was also altered so that the non-oil parts of the seed would make better animal feed. To change the genes, the rape seeds were subjected to powerful chemicals that mutated the genes. Most of the seeds had genes so damaged that they couldn't grow. The best seed became the original canola, which is short for “Canadian oil, low acid.” All canola oil contains these mutated genes—even organic canola. But canola is not the only oil seed to have undergone chemical or radiation mutation.

Soybeans, flax seeds, and sunflower seeds have all been altered by mutation. In fact, over 2000 food plants have been altered by mutation. These types of induced mutation are considered “traditional” breeding methods and no mention is required on the labels. This type of breeding does not violate organic labeling.

Genetic engineering

Another group of methods to alter seeds is called genetic manipulation or genetic engineering. Genetic engineering includes inserting genes from other plants, or even animals into the oil seed. There are two common methods. The first method uses a “gene gun” to fire tiny slivers of metal coated with a new gene. The second method uses bacteria to transfer the new genes. Both methods are widely used to alter the seeds used for oil.

Although the original canola oil was not genetically engineered, many newer varieties of canola have had their genes altered. Genetic engineering was used to create varieties of canola that are reduced in saturated fats, that are reduced in ALA, and that have differing amounts of oleic acid. These engineered varieties of canola are not considered organic. Corn, soybeans, and cottonseed have also been genetically engineered. Many of the other oil seeds are in the process of being genetically altered.

There are several oils on the market that have not been altered. Olive oil has not been mutated or genetically engineered. So far, palm oil, peanut oil, and safflower oil are all free of mutations or genetic manipulations. Sunflower oil has been mutated, but has not yet been altered by genetic engineering. There are plans to alter palm oil to lower its lauric acid content. As time goes on many of these oils will be marketed with foreign genes inserted.

Do the oils that have been altered genetically have health dangers? The best answer is that we do not know. Human safety studies are just not done by the companies that make the seeds nor are they done by our government. Because the oils are not labeled as to whether or not they have been genetically altered, future studies will not be able to tell if they are dangerous. In some parts of the world such as Europe and Japan, genetically altered food crops are not allowed. However, in the United States, the vast majority of the corn and soybean crops have been genetically engineered. Time will tell if these are safe.

References:

Epstein, S., "Role of the Insulin-Like Growth Factors in Cancer Development and Progression," Journal of the National Cancer Institute, Vol. 93, No. 3, 238, 2001

Kalantzi, OI, Ealcock, R, Johnston, PA, Santillo, D, Stringer, RL, Thomas, GO, and Jones, KC, "The Global Distribution of PCBs and Organochlorine Pesticides in Butter," Environmental Science and Technology, Vol. 10 No. XX.XXXX, 2001.

Loutfya, N, Fuerhackera, M, Tundob, P, Raccanellic, S, and Tawfic Ahmedd, M, "Monitoring of polychlorinated dibenzo-p-dioxins and dibenzofurans, dioxin-like PCBs and polycyclic aromatic hydrocarbons in food and feed samples from Ismailia city, Egypt," Chemosphere, Volume 66, Issue 10, January 2007, Pages 1962-1970.

Prosser, CG, Fleet, IR, Corps, AN, "Increased secretion of insulin-like growth factor I into milk of cows treated with recombinant derived bovine growth hormone," J Dairy Res 1989;56: 17–26.

Chapter 9: Comparing Less Common Oils

Summary

This chapter outlines the less common oils. The healthiest oils are rich in vitamin E. Wheat germ oil is the edible oil with by far the highest amount of vitamin E. A healthy oil needs to have a nice balance of the essential fatty acids. Perilla seed oil and chia oil both have generous amounts of the hard-to-get essential fatty acid, alpha-linolenic acid. Oils used for frying need a low level of essential fatty acids and a higher amount of oleic acid and saturated fatty acids. Cashew is a good example of a stable frying oil with 61% oleic acid, 20% saturated fatty acids, and only 17% of the essential fatty acids. In addition, cashew oil has a high amount of vitamin E. Natural antioxidants such as vitamin E help stabilize some oils during heating. The standard serving size in this chapter is one ounce (about 28 grams), which is approximately two tablespoons of each oil or butter.

Uncommon oils

There are many oils used around the world for special flavors or because of their unique fatty acids. These oils can be squeezed from seeds, fruits, and grains. This chapter presents a quick look at many of the commercially available oils. Please note that the percentages of the different fatty acids are approximate. Fatty acid content varies from different locations and throughout the year. To make this chapter more readable I have often averaged the percentages of fatty acids from several studies.

Almond oil

Almond oil (Prunus species or Amygdalis communis) has a pleasant smell and a yellow color. It is often used for massage. It is rich in oleic acid (65–80%), but its fatty acid composition can vary widely. It contains 17% linoleic acid, but almost none of the other essential fatty acid. Almond oil is low in saturated fatty acids, with only 5%. It has good stability to resist oxidation and stays clear in cold conditions. Vitamin E content is 240-390 mg/kg, which means that one serving provides over half of the minimum requirement for vitamin E for one day.

Amaranth oil

Amaranth oil (Amaranthus cruentus) comes from a grain containing only about 7% oil. The grain is easy to grow and rich in balanced protein. Amaranth oil contains about 22% saturated fatty acid and 22% oleic acid. It is high in the essential fatty acid linoleic acid at about 45%. It is high in squalene, which is rare in vegetable oils. Squalene is also found in olive oil and wheat germ. Squalene is a raw material for production of cholesterol in the body. Squalene is used as a skin moisturizer.

Apricot kernel oil

Apricot oil (Prunus armeniaca) is made from the kernel of the apricot fruit. The oil is similar to almond oil, but less expensive. It is used in cosmetics and as a specialty oil for food use. It is high in oleic (66%) and linoleic acids (26%). Apricot kernel oil has a low content of vitamin E (40 mg/kg), which means that one serving provides less than one-twentieth of the minimum requirement for vitamin E for one day. Apricot oil has some phospholipids. It has excellent cold weather stability.

Avocado oil

Avocado (Persea americana) is one of the few fruits rich in oil. The oil has a mild odor and is pale yellow. The oil comes from the fruit rather than from the seed. This oil is easily absorbed into your skin. Avocado oil is rich in chlorophyll. There are some saturated fatty acids, about 10-20% of myristic acid. Levels of oleic acid are high at 65%. Linoleic acid content is good at 10-15%. Avocado oil contains some plant sterols and E (112-201 mg/kg), which means that one serving provides one quarter of the minimum requirement for vitamin E for one day.

Figure 71 Graph of vitamin E in less common oils

Black currant oil

Black currants (Ribes nigrum) are similar to small grapes. Currants are used to make juice and jam. The oil is made from the seeds, which are a byproduct of juice and jam production. The main production of black currant oil is Europe. The principle fatty acid is linoleic, making up 47% of the oil. Black currant oil is one of the few sources of gamma-linolenic acid, of which the oil contains 17%. Alpha-linolenic acid content is 14%. The oil is 9% saturated. Oleic acid content is low at 11%. There is also a small amount of stearidonic acid (18:4 n-3), about 3%. Vitamin E content is 250 mg/kg, which means that one serving provides one half of the minimum requirement for vitamin E for one day.

Borage oil

Borage (Borago officinalis) is also known as starflower and originates in Syria. Borage oil is best known for its high content of gamma-linolenic acid. Gamma-linolenic acid is also found in high amounts in black currant and evening primrose oils. Gamma-linolenic acid has been used in the treatment of premenstrual syndrome, multiple sclerosis, and eczema. Borage oil is about 14% saturated with myristic acid as the primary saturated fatty acid. The oil is a little low in oleic acid. Linoleic acid is fairly high at about 38%. Vitamin E content is 200 mg/kg, which means that one serving provides one third of the minimum requirement for vitamin E for one day. Gamma-linolenic acid content is highest of any oil at 23%. By comparison, gamma-linolenic acid content is 10% in evening primrose oil and 17% in blackcurrant oil.

Figure 72 Graph of gamma-linolenic acid in some oils

Candlenut oil

Candlenut (Aleurites moluccana) is known in the Hawaiian Islands as kukui. The mature nuts can be broken in half and lighted with a match to function as a candle. The oil contains very little saturated fat (under 10%). The oil is rich in linoleic acid (42%) and very rich in alpha-linolenic acid (28%). Kukui nut oil is used in cosmetics and has been recommended for the treatment of burns. The meat of the kukui nuts are mildly toxic when raw because of the saponin and phorbol content.

Caraway oil

The seeds of caraway (Carum carvii) are technically fruits. Caraway seeds are added to some rye bread as flavoring. Caraway seeds retard the yeast, thus making the rye bread denser. Caraway seed oil contains petroselinic acid (18:1 n-12c), a positional isomer of the monounsaturated oleic acid (18:1 n-9c). Caraway seed oil contains 40% petroselinic acid. Carrot seed oil and coriander seed oil have even more petroselinic acid, 70% in carrot, 53% in coriander. Oils containing petroselinic acid can be used to manufacture nylon, potentially replacing a less environmental friendly process.

Cashew oil

Cashew trees (Anacardium occidentale) are native to Brazil. Cashew nut oil contains about 20% saturated fats, 12% palmitic acid, and 8% stearic acid. There is a generous amount of oleic acid in the oil, about 61%. The essential fatty acid linoleic acid is in the amount of 17%. Content of vitamin E totals 760 mg/kg, which means that one serving provides one and a half times the minimum requirement for vitamin E for one day.

Cherry oil

A main producer of cherries (Prunus cerasus) is Turkey. Cherry oil is sold cold-pressed and unrefined for salad dressings, baking, and for skin care products. The pits are a byproduct of cherry juice production. Cherry oil is quite unsaturated with 35% oleic acid and 45% linoleic acid. Cherry oil contains about 10% of an unusual trans fatty acid called alpha-eleostearic acid. Eleostearic acid (18:3 n-5t,7t,9c) is triply unsaturated trans isomer of alpha-linolenic acid (18:3 n-3,6,9). Eleostearic acid is also found in tung oil.

Chia oil

Chia seeds (Salvia hispanica) are native to Mexico and were cultivated by the Aztecs. Chia seed oil contains a large amount of the difficult to obtain alpha-linolenic acid, about 58%. With 20% linoleic acid, chia seed oil is capable of correcting the overabundance of linoleic acid in many American diets. Chia seed oil contains about 10% saturated fats and 8% oleic acid. Chia seeds are known as salba in Peru.

Echium oil

Echium seeds (Echium plantagineum) are low in saturated fatty acids with a combined 11% of palmitic and stearic acids. Oleic acid content is modest at 14%. Linoleic acid content is modest at 14%. One distinguishing feature is the somewhat high gamma-linolenic acid content of 9 to 12 percent. ALA content is high at 31% and gives a ratio of 2 to 1 for ALA to the other essential fatty acid, linoleic acid. The unusual thing about echium oil is its 9-12% content of stearidonic acid (Berti, 2007).

When we biosynthesize EPA from ALA, the first step is to use the enzyme delta-6 desaturase to convert ALA into stearidonic acid. This enzymatic conversion may be the principle rate-limiting step in the production of EPA. By supplying stearidonic acid directly, echium oil may boost EPA levels more effectively than oils high in ALA, but lacking stearidonic acid. Black currant oil and hemp oil are the only other commercial oil with stearidonic acid and contain just 2-3%. Echium oil is being used in cosmetic products for wrinkles and sun damage. Toxic pyrrolizadine alkaloids have not been found in the oil.

Figure 73 Graph of oleic acid in some less common oils

Evening Primrose oil

Evening primrose oil (Oenothera biennis) contains about 10% of the rare gamma-linolenic acid. It is also quite high in linoleic acid, containing about 72%. Evening primrose oil is widely used for premenstrual syndrome and for multiple sclerosis, although science has not confirmed the efficacy of these uses. It contains only 9% oleic acid. Vitamin E content is quite high at 500 mg/kg, which means that one serving provides the minimum requirement for vitamin E for one day.

Gold of Pleasure oil

Gold of pleasure (Camelina sativa) is called false flax because it contains a high amount of alpha-linolenic acid, about 35%. Gold of pleasure produces a large amount of oil without inputs of fertilizers and pesticides. The oil contains about 15% oleic acid and 20% linoleic acid. Vitamin E content is 170 mg/kg, which means that one serving provides one third of the minimum requirement for vitamin E for one day. It is unusual in its content of fatty acids with 20 and 22 carbons. This oil is highly unsaturated, but quite stable in regard to oxidation.

Grapeseed oil

Grapeseed oil (Vitis vinifera) is a gourmet oil that is also used in cosmetics. Grape seeds are a byproduct of the wine industry. There is not too much oil in grapeseeds, just from 10 to 20%. The oil is high in linoleic acid at 60-75%. It is low in saturated fats, just 9-14%. Oleic acid is at 12 to 25%. Vitamin E content is 288 mg/kg, which means that one serving provides one half of the minimum requirement for vitamin E for one day. Polycyclic aromatic hydrocarbons can contaminate grapes and grape seeds, but these compounds are mostly removed during the bleaching phase of processing.

Figure 74 Graph of linoleic acid in some less common oils

Hazelnut oil

Hazelnuts (Corylus avellana) are also called filberts. Hazelnuts are used in candy to make praline and chocolate truffles. The oil is rich in oleic acid, making up to three-quarters of the oil. Linoleic acid is present at about 19%. The oil is low in saturated fats. Hazelnut oil is rich in vitamin E with 472 mg/kg, which means that one serving almost meets the minimum requirement for vitamin E for one day.

Hemp oil

Hemp seed oil (Cannabis sativa) has some gamma-linolenic acid (0-5%), enough so that the oil may increase levels of gamma-linolenic acid in the bloodstream. It is low in saturated fats (about 8%). Oleic acid levels are low, but present at about 12%. Vitamin E levels are negligible at only 10 mg/kg. Hemp oil has a high content of alpha-linolenic acid, about 15-25%. The primary fatty acid is linoleic acid (almost 60%). The ratio of the essential fatty acids is one to three, which is an ideal ratio of these two fatty acids. The growing of hemp is banned in the United States, so hemp seed oil must be imported.

Honesty seed oil

Honesty seed oil (Lunaria annua) is high in nervonic acid (24:1 n-9c). Nervonic acid may have usefulness in multiple sclerosis to reduce demyelination of the nerve sheath (Sargent, 1994) . Nervonic acid plays a part in the biosynthesis of myelin. Nervonic acid is also found in the sphingolipids in the white matter of the brain. The oil contains about 22% of nervonic acid. There is also a very high content of erucic acid (22:1 n-9c), about 41%.

Macadamia nut oil

Macadamia nuts (Macadonia integrifolia) are one of the nuts richest in oil. About 80% of the oil is in the form of various monounsaturated fatty acids. The oil is a rich source of palmitoleic acid (16:1 n-7c). Oleic acid content also high making up about 60% of the oil. The oil is used in skin care. Stability of macadamia nut oil is low because of the low levels of vitamin E.

Mango oil

Mango (Mangifer indica) is consumed in large quantities as fruit, so the kernels are available for oil as a byproduct. The oil content of mango kernels is low at about 10%. Saturated fats are high for a vegetable oil at about 25%. Oleic acid content is approximately 45%. Essential fatty acid content is low, containing only 5% of linoleic acid. Mango oil can be fractionated to provide an olein that is soothing to skin. The stearin made from mango oil can serve as a trans fat free margarine or it can be used as a cocoa butter substitute.

Marigold oil

Marigold oil (Calendula officinalis) has an unusual fatty acid, calendic acid. Calendic acid (18:3 n-6c,8t,10t) is a trans conjugated isomer of alpha-linolenic acid. It has a structure similar to conjugated linoleic acid. Marigold oil is very high in calendic acid (about 60%). The processed oil can be used to replace volatile organic compounds in alkyd paints. Vitamin E content of the crude oil is quite high at 1820 mg/kg, which means that one serving supplies over three times the minimum requirement for vitamin E for one day.

Nigella oil

Nigella (Nigella sativa) is also known as black cumin. The seeds are used as a spice in Middle Eastern and Indian cuisine. The oil contains thymoquinone, which has been reported to reduce the growth of cancer, especially prostate cancer (Tingfang, 2008). Saturated fat content is about 10%. Oleic acid is about 35%. Linoleic acid is high, averaging 45%. The seed of nigella has an active lipase enzyme that releases free fatty acids during storage.

Niger oil

Niger oil (Guizotia abyssinica) originally comes from Ethiopia. It is rich in the alpha-tocopherol fraction of vitamin E. Linoleic acid content is very high at 75% of the seed oil. The oil contains about 18% saturated fatty acids. Oleic acid content is low at 9 %. Vitamin E content is high at 750 mg/kg, which means that one serving one and one-half times the minimum requirement for vitamin E for one day.

Figure 75 Graph of saturated fats in some less common oils

Nutmeg butter

Nutmeg butter (Myristica malabarica) has been reported to be used as a flavoring in Cola Cola. It is also used in tooth paste and cough syrup. The oil is numbing on skin contact. Myristic acid may have been named after this oil, which is very high in myristic acid, containing 40% and up to 72%. Vitamin E content is almost nonexistent at 2 mg/kg. It contains a hallucinogenic component, myristicin, with potential neurotoxic effects.

Oat oil

The seed of this grain (Avena sativa) has little oil. Like corn, the seeds contain about 6% oil. Saturated fats are somewhat high at an average of 21%. Oleic acid content is variable between 20% and 50%. Linoleic acid content is good and usually between 25% and 50%. Alpha-linolenic acid is low but present (about 3%). Vitamin E content is moderate at 144 mg/kg, which means that one serving provides one-quarter of the minimum requirement for vitamin E for one day. Oat oil contains some mono- and di-glycerides, free acids, sterols, glycolipids, and phospholipids (20%). The oil has reported appetite suppressant properties. The oil is used in cosmetics because of the glycolipid content. The policosanol contained in it may lower blood cholesterol (Mirkin, 2001).

Passionfruit seed oil

This tropical fruit seed (Passiflora edulis) contains about 20% oil. The oil is used as a gourmet oil for use in specialty foods and salad dressings. The seed oil contains 60% linoleic acid and is 10% saturated. Oleic acid levels are from 14-20%. This is a nice oil for skin care because of the rich content of linoleic acid.

Figure 76 Graph of ALA in some less common oils

Perilla seed oil

Perilla seeds (Perilla frutescens) are known as shiso and can be found in Asian herb stores. Perilla seeds are similar in composition to flax seeds. The alpha-linolenic acid content is quite high at an average of 61%. Linoleic acid content is 16%, so the ratio between the fatty acids is as favorable as flax seeds. Oleic acid content is low at an average of 14%.

Pistachio nut oil

Pistachio nuts (Pistachio vera) are native to Greece and the Middle East. Pistachio nuts are rich in oil, containing about 60%. The oil is used for cooking or frying in the Middle East. Average saturated fat content is 13%. Oleic acid makes up the bulk of the oil with a content of 69%. Linoleic acid content is low at 17%. Vitamin E content is 190 mg/kg, which means that one serving provides one-third of the minimum requirement for vitamin E for one day.

Poppy seed oil

Poppy seeds (Papaver somniferium) are used for bird feed and for decorating bread rolls. Opium is not present in the seed of the poppy. Poppy seed oil is very rich in linoleic acid, averaging 72%. It is only 10% saturated. Oleic acid content (11%) and alpha-linolenic acid (5%) are low. Vitamin E content is 250 mg/kg, which means that one serving provides half of the minimum requirement for vitamin E for one day.

Purslane seed oil

Purslane (Portulaca oleracea) is a common weed in the United States. Purslane seed oil is rich in alpha-linolenic acid, containing 26%. Linoleic acid content is reported to be 33%. This means that the essential fatty acids are present in roughly equal amounts. Oleic acid is present at 18%. Purslane seed oil is 19% saturated.

Rice bran oil

Rice bran (Oryza sativa) is produced when brown rice is milled into white rice. Only a small quantity of the available rice bran is made into rice bran oil, less than a million tons yearly. The oil is used in salad dressings. Rice bran oil is an excellent frying oil because of the high vitamin E content and the content of oryzanols (1-2%). Gamma-oryzanol is an antioxidant that may lower blood cholesterol (Cicero, 2001). The oil is made up of 16% saturated fats, mostly palmitic acid. It is rich in oleic acid with nearly half (42%) of the oil in this form. Rice bran oil is also rich in linoleic acid (37%). Phospholipids make up 5% of the oil. Rice bran oil contains waxes, sterols, squalene, and vitamin E (323 mg/kg), which means that one serving provides almost two-thirds of the minimum requirement for vitamin E for one day.

Shea butter

Shea butter (Butyrospermum parkii) comes from West Africa. Saturated fat content can be as high as 66%. Most of the saturated fat is stearic acid. Oleic acid content is also variable from 33-68%. Linoleic acid content is quite low (averaging 6%). Shea butter has no appreciable amount of vitamin E. Shea butter contains polyisoprene, which is a rubbery hydrocarbon. When fractionated, shea butter stearin can be used to replace cocoa butter.

Walnut oil

Walnut oil (Juglans regia or Juglands nigra) is used as a gourmet salad oil. Walnut oil is rich in linoleic acid (55%) and alpha-linolenic acid (14%). This is an ideal ratio between the two essential fatty acids. Walnut oil is very rich in vitamin E with a content of 432 mg/kg, which means that one serving provides almost enough of the minimum requirement for vitamin E for one day. It may be extracted with hexane if not organically processed. It also may be extracted with supercritical carbon dioxide.

Wheatgerm oil

Wheat germ oil (Triticum aestivum) is famous for its high amount of vitamin E, 1500-2500 mg/kg. This means that one serving provides almost four times the minimum requirement for vitamin E for one day. It is also a good source of the healthful octacosanol and cholesterol-lowering polycosanol. Linoleic acid content is very high at 60%. There is a little alpha-linolenic acid, about 5%. This oil spoils rapidly. To prevent rancidity of this highly unsaturated oil, cold pressing, packaging in glass with nitrogen gas, and refrigeration is necessary.

References:

(Berti, 2007) M. Berti, B.L. Johnson, S. Dash, S. Fischer, R. Wilckens, and F. Hevia, "Echium: A Source of Stearidonic Acid Adapted to the Northern Great Plains in the US," Issues in new crops and new uses. 2007. J. Janick and A. Whipkey (eds.). ASHS Press, Alexandria, VA.

(Cicero, 2001) A. F. G. Cicero, A. Gaddi, "Rice Bran Oil and gamma-Oryzanol in the Treatment of Hyperlipoproteinaemias and Other Conditions," Phytotherapy Research, 2001, Volume 15, Issue 4, Pages 277 - 289.

(Mirkin, 2001) Mirkin A, Mas R, Martinto M, Boccanera R, Robertis A, Poudes R, Fuster A, Lastreto E, Yañez M, Irico G, McCook B, Farré A., "Efficacy and tolerability of policosanol in hypercholesterolemic postmenopausal women," Int J Clin Pharmacol Res. 2001;21(1):31-41.

(Sargent, 1994) J Sargent, K Coupland, "Application of specialized oils in the nutritional therapy of demyelating disease," Lipid Technology, 6, 10–14 (1994). Also see Martinez M, "Polyunsaturated fatty acids in the developing brain, erythrocytes and plasma in peroxisomal disease: Therapeutics implications," 1995, J. Inherit. Metab. Dis., 18, Suppl. 1, 61–75. Also see Moser AB, Kreitner N, Bezman L, Lu S, Raymond GV, Naidu S, Moser HW, "Plasma very long chain fatty acids in 3,000 peroxisome disease patients and 29,000 controls," 1999, Ann. Neurol., 45, (1), 100–110.

(Tingfang, 2008) Tingfang Yi, Sung-Gook Cho, Zhengfang Yi, Xiufeng Pang, Melissa Rodriguez, Ying Wang, Gautam Sethi, Bharat B. Aggarwal, and Mingyao Liu, "Thymoquinone inhibits tumor angiogenesis and tumor growth through suppressing AKT and ERK signaling pathways," Mol Cancer Ther. 2008 July; 7(7): 1789–1796.

Chapter 10: Comparing the Oils in Food

Summary

This chapter analyzes nuts and other common fatty foods to see which are healthiest. The healthiest fatty foods have high levels of vitamin E to protect the delicate oils. Sunflower seeds, almonds, and hazelnuts are all high in vitamin E. The best fatty foods will have a high level of the hard-to-get essential fatty acid, alpha-linolenic acid. English walnuts and soybeans are healthy sources of this essential fatty acid.

Some common food selections are just too high in overall fats. Potato chips and chicken are two examples of common foods that can contribute too much fat to the diet. Excessive intake of saturated fats is the number one cause of heart disease. Potato chips, cheese, doughnuts, and chicken can all be high in saturated fats. Coconut meat is the only non-animal product that is high in saturated fat.

Fats in food

The best dietary source of fats and oils is whole food, as opposed to bottled oils. This chapter will compare the fatty acids in whole food. We will look at their content of essential fatty acids, vitamin E, monounsaturated fatty acids, and saturated fatty acids. The food selections in this chapter will not include many vegetables, grains, or fruit, because they are low in fats and oils. The information in this chapter comes from the United States Department of Agriculture Food Composition Database released in September 2008 (courtesy of the Diet Doctor software). The goal of this chapter is to help you make informed decisions about which food choices are healthiest.

Nuts and Seeds

Nuts and seeds are rich in fats and oils. Some of them are rich sources of vitamin E as well. There is a large variability in the content of fatty acids in nuts and seeds. This section will visually present the differences with graphs.

Oleic acid in nuts and seeds

The chart below shows the oleic acid content of some common nuts and seeds. Oleic acid is monounsaturated. Oleic acid is considered a healthy oil when it replaces saturated fats in the diet. With just one double bond, it is more stable than the polyunsaturated oils. Oleic acid resists rancidity and oxidation when compared to the polyunsaturated fats. Of course, vitamin E and beta-carotene are also needed to inhibit oxidation.

Figure 77 Graph of oleic acid in common nuts and seeds

As we can see from the graph above, oleic acid is easy to find in nuts and seeds. Oleic acid is the most common fatty acid in nature. Flax seeds and English walnuts are low in oleic acid because they contain so much of the essential fatty acids. Coconut meat is low in oleic acid because it is almost completely made up of saturated fats.

Saturated fats in nuts and seeds

Some nuts have a high content of saturated fats. Excessive saturated fats raise blood cholesterol and increase the risk of heart attacks and strokes. Most people do not take in excessive saturated fats from nuts and seeds.

Figure 78 Graph of saturated fats in selected nuts and seeds

As can be seen from the chart above, coconut meat is the only nut meat that contains a high percentage of saturated fats. Just two small servings of one-quarter cup of coconut meat contribute more saturated fat than is healthy for one day. Luckily, few Americans eat much coconut meat. Brazil nuts and macadamia nuts also have a fairly high content of saturated fats. It is not normal for most people to eat enough Brazil nuts or macadamia nuts to raise blood cholesterol. The other nuts and seeds are low enough in saturated fat that they are unlikely to raise blood cholesterol levels.

Vitamin E in nuts and seeds

The content of vitamin E varies widely between the different nuts and seeds. Vitamin E is crucial to protect the inside of the arteries (the endothelium) from oxidation. Vitamin E is especially needed in fatty foods that have a high content of polyunsaturated fatty acids. Polyunsaturated fatty acids such as the essential fatty acids must be protected with vitamin E.

Figure 79 Graph of vitamin E in selected nuts and seeds

The graph above shows that sunflower seeds, almonds, and hazelnuts are rich in vitamin E. Just three ounces (100 grams) supply enough vitamin E for a day. Two servings of pine nuts, peanuts, and Brazil nuts supply enough vitamin E to meet the minimum amount needed in one day. All of the other nuts and seeds listed above are low in vitamin E. When choosing nuts and seeds, the vitamin E content is a good guide to healthfulness.

Alpha-linolenic acid in nuts and seeds

Getting enough of the essential alpha-linolenic acid (ALA) is difficult. Some nuts and seeds are good sources. Many nuts and seeds have little of this hard-to-obtain essential fatty acid. Without enough ALA, there can be an overproduction of arachidonic acid leading to inflammation and excessive blood clotting.

Figure 80 Graph of ALA in selected nuts and seeds

As can easily be seen from the graph above, flax seeds are the highest source of ALA. Flax seeds have the capacity to correct the common overabundance of linoleic acid found in many diets. Perilla seeds and chia seeds (not shown above) also have an abundance of ALA. It is interesting to note the difference between black walnuts and English walnuts as to their content of ALA. English walnuts are one of the few common foods that have a high amount of ALA. Since the daily need for ALA is only 2-5 grams, even nuts and seeds with a small amount of ALA contribute to an acceptable daily total. In most diets few food servings contribute more than 0.2 grams of ALA.

Linoleic acid in nuts and seeds

Getting enough of the essential fatty acid linoleic acid is easy. Getting too much is also easy. We need about 10 to 17 grams of linolenic acid every day (based on a 2200 kcal intake). If we take in more, it can adversely affect the balance between essential fatty acids. The ideal balance between fatty acids is 2 to 4 times as much linoleic acid as ALA. Acceptable balances range up to ten to one. Unfortunately, most people in the developed world have balances of 15 or even 20 to one times as much linoleic acid as ALA.

Figure 81 Graph of linoleic acid in selected nuts and seeds

The graph above shows the abundance of linoleic acid in many nuts and seeds. English walnuts have the most linoleic acid, but since they also contain so much of the other essential fatty acid, they have a nice balance (about 4 to 1). Black walnuts have enough ALA to be somewhat balanced in essential fatty acids. Many of the other nuts and seeds have too much linoleic acid and too little ALA. This does not mean that they are unhealthy. Remember that these nuts and seeds are the best dietary source of vitamin E. If some flax seed powder is included in a diet rich in linoleic acid, it will help to adjust the balance of essential fatty acids.

Fatty acids in commonly selected food choices

The food selections considered in the chart below are all high in fat. For each food, the quantity considered is one serving. Serving size is different for different people at different times. The selections below are a few common fatty food selections representative of the food groups.

Food	Serving	Grams
Canned olives	20 olives	64
Avocado	1/2 large	201
Almonds	1/2 cup	50
Sunflower seeds	1/2 cup	70
Cheddar cheese	3 slices	100
Milk, whole	1 cup	250
Scrambled eggs	2 eggs	120
Pinto beans	1 cup	172
Peanut butter	2 tablespoons	64
Tofu, firm	1 cup	126
Ground beef	3 ounces	85
Chicken	1/4 chicken	250
Salmon nuggets, breaded	1 serving	125
Salmon, canned	1 can	125
Soybeans, sprouted, stir-fried	1 cup	125
Beans, navy, sprouted, boiled	1 cup	125
Potato chips, plain, salted	8 oz. bag	227
McDonald's French fries	medium serving	114
Cookies, chocolate sandwich	10 cookies	117
Doughnuts, chocolate frosted	2 doughnuts	117
Ice creams, chocolate	8 oz.	130

Figure 82 Chart of food servings to be analyzed

Total fat in food

Which food choices have the most fat? The quantity of fat in a diet is important. Many Americans eat too large a quantity of fats and oils each day. This can contribute to elevated triglyceride and cholesterol levels in the blood.

Figure 83 Graph of total fat in common foods

The graph above shows the amount of total fat in selected food. It is easy to exceed the recommended maximum of fat intake with food selections such as potato chips. Peanut butter and avocados are considered healthy food, yet generous portions can also exceed the amount of fat needed. Much more important than the amount of total fat is the amount of saturated fat.

Saturated fat in food

Excessive saturated fats in the diet are the most important contributor to elevated blood cholesterol and the risk of heart attacks. Small amounts of saturated fats are not harmful, and are, in fact, unavoidable. The American Heart Association recommends a maximum of 7% of calories as saturated fat. Most government agencies and the World Health Organization set the maximum at 10% of calories. Saturated fat intake at 10% of calories will, depending on other dietary factors, allow the worsening of atherosclerosis. This clogging of the arteries may stop getting worse when the diet contains 7% of calories as saturated fat. A whole food, plant-based diet with saturated fat less than 5% can reverse the course of atherosclerosis as shown by the work of Dr. Caldwell Esselstyn (Esselstyn, 2001), Dr. Terry Shintani, Dr. Dean Ornish, Dr. John McDougall, and others. To reduce saturated fatty acids in the diet, the first step is recognizing where they occur in food.

Figure 84 Graph of saturated fat in common foods

The graph above visually displays where many Americans get excesses of saturated fat. Cheese is often the largest contributor of saturated fat to average diets. Junk food such as potato chips and doughnuts also are major contributors of saturated fatty acids. Chicken has a high content of saturated fats. Ice cream, like many dairy products, contributes heavily to saturated fat intake. Salmon has low levels of saturated fats when compared to other animal products. Nuts, seed, tofu, and beans are all very low in saturated fats.

Cholesterol in common food selections

Dietary cholesterol is not the predominant factor in raising blood cholesterol, but it is a contributing factor. Dietary cholesterol is absorbed and transported in the bloodstream in chylomicrons without first going through the liver. Some of this dietary cholesterol may be oxidized. Oxidized cholesterol (oxysterols) have been shown to damage the inside of the arteries, which is a contributing factor in atherosclerosis. Also, dietary cholesterol may not be protected by vitamin E since vitamin E is very low in most of the food sources that contain cholesterol. Humans have no dietary need for cholesterol and it is safest to avoid all sources of dietary cholesterol (animal products).

Figure 85 Graph of cholesterol in common foods

The graph above shows the very high content of cholesterol in eggs. Other food choices with high amounts of cholesterol include chicken, cheese, beef, and ice cream. All of these animal products also have a high content of saturated fat. The combination of high amounts of saturated fat and high amounts of cholesterol increases the risk of heart attacks and strokes.

Trans fats in selected foods

It is healthiest to avoid trans fats entirely. Below are some food selections with trans fats.

Figure 86 Graph of trans fat in common foods

The highest sources of trans fats are fried food and baked, packaged food. Animal products such as dairy products, beef, and eggs can also make up a significant proportion of trans fats in diets.

Monounsaturated fats in selected food

Oleic acid makes up most of the monounsaturated fatty acids in food. Monounsaturated fats are considered healthful when they replace saturated or trans fats in the diet.

Figure 87 Graph of monounsaturated fat in common foods

The graph above displays the amount of monounsaturated fatty acids in selected food sources.

Linoleic acid in selected food sources

Linoleic acid is an essential fatty acid. Linoleic acid is easy to obtain in most diets. It is healthier to keep linoleic acid consumption low enough so that it does not overpower the amount of the other essential fatty acid, ALA.

Figure 88 Graph of linoleic acid in common foods

The graph above shows the amount of linoleic acid in selected food choices. Sunflower seeds have a remarkably high content of linoleic acid. More than two servings of chicken or peanut butter in a day can start to contribute too much linoleic acid to a diet. Most people in the developed world who take in too much linoleic acid get it from bottled oils, rather than from food.

Alpha-linolenic acid in selected food sources

Alpha-linolenic acid (ALA) is difficult to get enough of in many diets. Outside of flax powder walnuts, and some oils, there is only a small amount of ALA in most food sources. Yet this nutrient is essential for the balanced production of eicosanoids to control blood clotting, the immune system, and inflammation.

Figure 89 Graph of ALA in common foods

The graph above shows the small amounts of ALA in food compared to our daily need. Although we may survive on lower amounts of ALA, optimum health and disease resistance may be compromised. Even for the highest source listed here of ALA, soybeans, it would take six servings to take in the daily recommended amount of ALA. The addition of ALA supplements such as flax powder is often needed to supplement diets too low in ALA.

EPA and DHA in selected food sources

The long-chain polyunsaturated fatty acids EPA (eicosapentanoic acid) and DHA (docosahexanoic acid) are not essential because we can make them in our bodies. Most of the EPA and DHA in our bodies is made in the body, and outside sources provide little, if any of our EPA and DHA.

Figure 90 Graphs of EPA and DHA in food

Only three of the selected food sources contained any EPA or DHA. It is surprising that chicken has more EPA than salmon. This may be due to the use of fish meal added to chicken feed. The content of EPA will vary according to animal feed. DHA is made by algae and eaten by fish. Fatty fish such as salmon, sardines, and mackerel are common sources.

Vitamin E in selected food sources

Vitamin E is needed wherever there are unsaturated fatty acids to prevent oxidation.

Figure 91 Graph of vitamin E in selected foods

The graph above visually illustrates the vitamin E content of some common food choices. Sunflower seeds and almonds are excellent sources of vitamin E. Although potato chips contain vitamin E (from the oils used in frying), they contain too much fat and too much saturated fat to be considered healthy. Peanut butter and avocados are both good sources of vitamin E. Chicken is unusual for an animal product in that it contains some vitamin E. The other food sources listed contain little vitamin E. With these other food choices, it would take too many servings to be practical to obtain the minimum amount of vitamin E for a day.

References:

(Esselstyn, 2001) Esselstyn CB Jr., "Resolving the Coronary Artery Disease Epidemic through Plant-Based Nutrition," Preventive Cardiology, 2001; 4: 171-177.

Part IV: Powerful balances

Chapter 11: Eicosanoid precursors: how EPA is made

Summary

To become more useful to the body, the essential fatty acids must first be lengthened and desaturated. The essential omega-3 fatty acid is converted to EPA. Enough EPA can be made in our bodies if certain conditions are met. First of all, we need to take in 2-5 grams of the omega-3 essential fatty acid every day. The addition of walnuts and flax powder are excellent ways to boost intake of this essential omega-3 fatty acid. Second, we need to limit the amount of the omega-6 essential fatty acid. To accomplish this, it is best to get most of our fats from whole foods rather than refined oils. Nuts, seeds, avocados, and soy foods have moderate levels of omega-6s. When oils are needed, unhydrogenated canola and soybean oil have the best balance of omega-3 and omega-6.

Under certain conditions, supplementation with preformed EPA may be necessary. There are some factors that limit conversion of the essential fatty acids to EPA. People with hepatitis C or those who have diabetes may need extra EPA. People with several risk factors for heart disease including high blood triglycerides and cholesterol may benefit from supplementation. People whose diets do not provide the nutrients needed for internal production of EPA may also need supplementation. It is best to correct these limiting factors with adjustments of diet and fitness when possible. EPA supplementation can increase bleeding tendencies and lower immune response.

We also need DHA, which is made in our body from EPA. DHA is crucial for brain function and vision. The methods outlined for assisting EPA creation also assist DHA creation. If needed, capsules of DHA made from algae can be supplemented at about 200 milligrams daily.

How the essential fatty acids are elongated and desaturated

The two essential fatty acids are ALA (alpha-linolenic acid) and LA (linoleic acid). They are elongated and desaturated to become three eicosanoid precursors. These three eicosanoid precursors are EPA (eicosapentaoic acid), arachidonic acid, and dihomo-gamma-linolenic acid (DGLA). From these three eicosanoid precursors, our bodies can make all of the eicosanoids.

Eicosanoids will be covered in the next chapter. They are powerful signaling molecules that control inflammation and immunity. They are also important in controlling blood clotting.

EPA is elongated and desaturated to become DHA (docosahexanoic acid). Eicosanoids are not made from DHA, but DHA is important in the development of the brain and retinas. DHA plays an important role in the regeneration of the visual pigment rhodopsin. The active substances made from the 22-carbon DHA are sometimes called docosanoids.

Any fatty acid with more than one double bond is a poylunsaturated fatty acid (PUFA). All of the fatty acids that are made by elongating essential fatty acids are called long-chain poylunsaturated fatty acids. They are sometimes abbreviated in the literature as LC-PUFA.

The only abbreviations that you will need to remember to read this chapter are ALA, LA, EPA, and DHA. These stand for alpha-linolenic acid, linoleic acid, eicosapentanoic acid, and docosahexanoic acid, respectively.

Figure 92 Omega-3 and omega-6 eicosanoid precursors

As you can see from the figure above, only EPA is made from the omega-3 essential fatty acid alpha-linolenic acid, ALA. The other two eicosanoid precursors are made from the omega-6 essential fatty acid linoleic acid, LA. Let us take a look at how these eicosanoid precursors are made in a bit more detail.

Can our bodies make enough EPA or do we need to eat fish or fish oils?

The main source of preformed EPA is algae (Latin for seaweed). Wakame is a seaweed with 21 mg (milligrams) of EPA in a tablespoon. Some fish eat and concentrate EPA from algae into their fish oils. Salmon, sardines, and mackerel are the three most common fish to contain large amounts of EPA. A fillet of salmon can contain about 500 mg of EPA. EPA from fish or fish oils can be contaminated, and there are ecological and ethical implications with fishing and aquaculture.

EPA supplementation, whether with fish, fish oils, or with algae-derived EPA has some potential disadvantages. Fatty fish and EPA supplements made from fish can be contaminated with bioaccumulated toxic chemicals, such as polychlorinated biphenyls (PCB) and pesticides like DDT. Fish oils can increase bleeding tendencies. Fish oils also have the effect of lowering the power of the immune system. This is because leukotrienes made from omega-6 fatty acids (from arachidonic acid) are estimated to be 30 times more potent than leukotrienes made from EPA. Although lowering the intake of linoleic acid coupled with higher intake of ALA is less powerful in decreasing omega-6 eicosanoids (Raederstorff, 1992), this is a safer method of balancing both the immune system and bleeding tendencies.

On the other hand, our bodies make EPA from the essential fatty acid ALA. We can either depend on our bodies to make the correct amount of EPA or we can eat EPA directly in fish oil, algae, or seaweed. It is estimated from several studies that at least 5 to 10 percent of dietary ALA is converted inside the body to EPA. The recommended amount of ALA for a 2200 calorie (kcal) diet is 1% of calories or 2.4 grams. If we are eating 2.4 grams of ALA, then we can make 120 to 240 mg of EPA. There are several factors that can increase or decrease this conversion of ALA to EPA. In one study, the conversion of ALA to EPA in women was 21%. Based upon a 21% conversion and 2.4 g of ALA, the amount of EPA produced could be 500 mg (Davis, 2003). This is the same amount as is found in a fillet of salmon.

Dietary guidelines and intakes for EPA and ALA

International guidelines for the daily need for EPA range from about 250-1000 mg daily. Actual average intakes of EPA plus DHA in normal American omnivorous diets tend to be only 100-150 mg/day. Like cholesterol, the main source of EPA is endogenous (internal) production. The adequate intake for EPA, based upon a 2200 calorie (kcal) diet, from a National Institutes for Health study was 240 mg.

With a 2200 calorie (kcal) diet with 1-2% of calories as ALA (2.4-4.8 g ALA), EPA production in the body can meet these guidelines of 250 to 1000 mg per day. However, most diets do not have this much ALA. Most daily diets range from one-half to 2 g ALA. As we shall see, there are many factors affecting the conversion of ALA to EPA.

Figure 93 The formation of eicosanoid precursors

Competition for the desaturation enzymes

As you can see from the figure above, the essential fatty acids are first desaturated with the enzyme delta-6 desaturase. Delta-6 desaturase starts from the delta end of an essential fatty acid. It reaches in 6 carbon atoms and places a double bond―thus desaturating the fatty acid in this location. There is competition between ALA and LA for delta-6 desaturase. Delta-6 desaturase is also used in the desaturation of oleic acid, arachidonic acid, and in the conversion of EPA to DHA (two of these three are not shown above). So there is competition for delta-6 desaturase between these five different fatty acids.

Excess LA is common in diets. Excess LA will use up delta-6 desaturase so less is available to desaturate ALA or other fatty acids. An abundance of EPA, for instance from fish oil, will also leave less delta-6 desaturase available for desaturation of the essential fatty acids. The conversion of the essential fatty acid ALA to EPA and DHA takes place in an organelle called the endoplasmic reticulum, primarily in the cells of the liver (Arterburn, 2006).

Excess LA also reduces the expression of the genes that produce delta-6 desaturase (Benatti, 2004). Both competition for delta-6 desaturase and the suppression of the production of delta-6 desaturase can inhibit desaturation of ALA (and LA). Both are caused by the overconsumption of LA.

The ratio of LA to ALA

To ensure adequate production of eicosanoid precursors from ALA, dietary LA should be restricted. Production of arachidonic acid from LA has not been reported to be lacking. However, production of EPA form ALA can be limited by excess LA. It has been estimated that excess dietary LA can decrease conversion of ALA to EPA by 40-54% (Emken, 1994).

Estimates of the best ratio of LA to ALA range from 2 to 1 to 10 to 1. The 1993 report from the World Health Organization/Food and Agriculture Organization suggests a ratio of 5 to 1 to 10 to 1. The Canadian Scientific Review Committee recommends a ratio of 4 to 1 to 10 to 1. The Nordic Working Group on Diet and Nutrition recommends a ratio of 5 to 1. In Japan the recommendation is a bit lower, from 2 to 1 to 4 to 1. The National Institutes of Health suggests a ratio of 2 to 1 to 3 to 1. A study in India found that a ratio of 4 to 1 supports adequate conversion of ALA to DHA in healthy vegetarians. Looking at the production of desaturases, the optimal ratio for the maximum conversion of ALA to DHA may be 2.3 to 1. For people who do not eat fatty fish, the safest range is likely between 2 to 1 to 4 to 1. This ratio, however, is rare in vegetarian (or other) diets.

To achieve this ratio, adequate ALA must be consumed. For people who do not eat fatty fish on a regular basis, 2 to 5 grams per day of ALA is a healthy optimal intake. Clearly, LA also needs to be restricted. Salad dressings and liquid oils are the highest sources in many diets.

Figure 94 Graph of ALA content of some common oils

One ounce of soybean or canola oil (about two tablespoons) has enough ALA for one day. The graph above shows ALA in grams. As you can also see from the above graph, only canola and soybean oil have optimal ratios of LA to ALA. Butter has a good ratio, but almost no ALA. Even olive oil has a ratio of 14 to 1, upsetting the perfect balance. Oils such as corn and cottonseed have high ratios and should be used in small quantities, if at all. Sesame oil is unbalanced in its ratio of LA to ALA. Sesame oil is useful in cooking at medium heat, however, only small amounts should be used. The oils on the bottom of the graph above have negligible amounts of ALA and can be considered to be very unbalancing.

Some food types have high levels of LA that are hidden. Convenience food, processed and packaged food, and especially snack foods can have high levels of LA. In one diet, potato chips alone accounted for two-thirds of the LA in the diet, contributing 20 grams of LA.

Whole foods such as nuts, seeds, avocado, and soy products can contain moderately high levels of LA. These whole foods are not usually heavy contributors of LA to a diet. These foods can be excellent sources of vitamin E, trace minerals, and fiber.

Diet Name	Amount of LA	Amount of ALA	Ratio LA to ALA	Ratio of LA to ALA with 2 T flax powder
Mediterranean	12	1.3	9.4	2.9
Atkin's	14	0.8	18	3.7
American Diet	15	1.5	10	3.4
Zone	14	0.4	36	4.2
Transitional Vegetarian	29	1.4	21	6.5
Vegan Whole Food	12	1.1	11	3
Very Low Fat Ornish	4.2	0.5	8.4	1.4
Raw Vegan	32	2.3	14	6

Figure 95 Chart of the ratio of LA to ALA in selected diets

Looking at the eight diets in the chart above, you can see that it is rare for a diet to achieve a ratio under 10 to 1. With the addition of two tablespoons of flax powder to the diets, excellent ratios emerge. Remember that we need 2-5 grams of ALA in addition to a good ratio of LA to ALA for optimal production of EPA.

Hormones affect desaturation

In addition to fatty acid competition, several hormones affect the conversion of essential fatty acids to their longer-chain derivatives. Insulin is a hormone that tells cells to take in glucose and fatty acids. Insulin also stimulates delta-5 and delta-6 desaturases. Insulin becomes less effective if the diet contains too much saturated or trans fatty acids. On the other hand, a healthy intake of essential fatty acids makes insulin, and also the desaturases, more effective. Glucagon is a hormone that restrains cells from taking in glucose and fatty acids. Glucagon inhibits desaturase activity. This is how the hormones insulin and glucagon are involved in controlling delta-6 desaturase activity.

Figure 96 Effects of hormones on the desaturation of ALA

The thyroid hormone thyroxine stimulates delta-6 and delta-5 desaturase enzymes in the liver. Some other hormones inhibit these desaturases. Stress hormones inhibit desaturase activity. Prednisone is a common drug that mimics stress hormone activity. Prednisone inhibits desaturase activity. Aldosterone, another hormone, also inhibits both delta-6 and delta-5 desaturases. Cholesterol is a hormone precursor. Excess blood cholesterol inhibits the conversion of ALA to EPA. This control that hormones have over the desaturation of ALA and LA helps regulate the creation of eicosanoid precursors.

Nutrition and desaturation

To make these eicosanoid precursors, we need our elongase and desaturase enzymes properly nourished. Like many enzymes, elongase and desaturase need certain nutritional cofactors to function. Pyridoxine (vitamin B6), niacin (vitamin B3), magnesium, and zinc are some of the cofactors needed to elongate and desaturate long-chain fatty acids. Zinc and vitamin B6 are involved in the formation of delta–6 desaturase (Caldis-Coutris, 2002). Vitamin E is important to protect these unsaturated fatty acids from oxidation. Vitamin C is needed to recharge the antioxidant potential of vitamin E. Two molecules of vitamin E may also be needed in the mitochondrial conversion of ALA to DHA (Benatti, 2004). Deficiencies of biotin, calcium, and copper can limit desaturase activity (Davis, 2003). Deficiencies of iron and vitamin B12 may also limit conversion, but this is less certain (Horrobin, 1981).

Desaturation of ALA to EPA is enhanced by a well-nourished body with well-functioning hormone systems. Since these same nutrients are needed in a myriad of other vital processes, it is best to stay well nourished. Conversion in a poorly nourished diabetic person may be so inhibited that supplementation with EPA and/or DHA may be necessary.

Figure 97 Effects of nutrition on the desaturation of ALA

Other factors that affect desaturation

Exposure to radiation can damage polyunsaturated oils in the body. Alcohol consumption can interfere with conversion of ALA and LA to longer chain highly unsaturated fatty acids. Diabetes also can limit conversion. Excess blood fats, cholesterol, or sugars limit the activity of the desaturases. Trans fatty acids have also been found to interfere with desaturation of ALA and LA. Since much of the desaturase activity happens in the liver, hepatitis C can interfere with these desaturases. Desaturation has been seen to decrease slightly in the elderly.

Conversion of ALA to EPA, step by step

The first step in the conversion of ALA to EPA is the action of delta-6 desaturase on ALA.

Figure 98 Structural changes with delta-6 desaturase converting ALA to stearidonic acid

As shown above, delta-6 desaturase inserts a double bond six carbon atoms from the delta end of ALA. This changes the fatty acid from 3 to 4 double bonds. ALA with 3 double bonds is converted to stearidonic acid with 4 double bonds. Stearidonic acid is found in a few seed oils, such as echium oil (9-12%), hemp oil (2-3%), and black currant oil (2-3%). Taking stearidonic acid directly in the diet bypasses this step of the transformation of ALA into EPA.

Figure 99 Structural changes of the conversion of stearidonic acid to eicosatetraenoic acid

The second step changes the fatty acid by making it two carbon atoms longer. This is done with the enzyme elongase. Stearidonic acid, with 18 carbon atoms, is transformed into eicosatetraenoic acid with 20 carbon atoms.

Figure 100 Structural changes of the conversion of eicosatetraenoic acid to EPA

The final step in making EPA from ALA uses the enzyme delta-5 desaturase. This enzyme inserts another double bond five carbon atoms from the delta end. Eicosa means twenty, the number of carbon atoms. Penta means five, the number of double bonds. Notice how the molecule bends more as more double bonds are added.

Blood levels of EPA and arachidonic acid

Blood levels of arachidonic acid tend to be the same, regardless of the diet regime followed. This indicates that delta-6 desaturase may not be the limiting factor in creation of either arachidonic acid or EPA, since delta-6 desaturase is needed for both of these eicosanoid precursors. The ratio of LA to ALA, adequacy of ALA in the diet, and nutritional cofactors seem to be the main determinants of how much EPA is made in the body.

Most of the studies of populations comparing omnivores, vegetarians, and vegans show differences in the amount of EPA (and DHA) in blood. Most of these studies were looking at plasma and erythrocyte levels of EPA and DHA. Compared to people with omnivorous diets, averaging across seven studies, vegan EPA levels were found to be about half as high. In four of the studies, the levels were about 35% of omnivore levels. In a study on vegan children, EPA levels were higher, about two-thirds of the omnivorous children. Two studies showed no difference in blood EPA levels between vegans and omnivores, perhaps because dietary ALA levels were higher.

DHA levels in blood tended to be higher in vegans compared to EPA levels. Looking at seven studies, vegan levels of DHA in plasma and erythrocytes averaged about two-thirds the levels of omnivores.

Since vegetarians and vegans take in little or no dietary EPA or DHA, they need to be more careful about eating enough ALA and restricting dietary LA.

References:

(Arterburn, 2006) Linda M Arterburn, Eileen Bailey Hall, and Harry Oken, "Distribution, interconversion, and dose response of n#3 fatty acids in humans." Am J Clin Nutr 2006;83(suppl):1467S–76S.

(Benatti, 2004) Paola Benatti, MC, Gianfranco Peluso, MD, Raffaella Nicolai, PhD, and Menotti Calvani, MD, "Polyunsaturated Fatty Acids: Biochemical, Nutritional and Epigenetic Properties" Journal of the American College of Nutrition, Vol. 23, No. 4, 281–302 (2004) Published by the American College of Nutrition

(Bhathena, 2000) Bhathena, Sam J. "Relationship Between Fatty Acids and the Endocrine System," Biofactors; 2000, Vol. 13 Issue 1-4, p35.

(Caldis-Coutris, 2002) Nancy Caldis-Coutris, RD, Mike Namaka, MSc Pharm, PhD, Maria Melanson, MD, "Nutritional Management of Multiple Sclerosis,"Canadian Pharmacists Journal CPJ/RPC • June 2002.

(Davis, 2003) Brenda C Davis and Penny M Kris-Etherton, "Achieving optimal essential fatty acid status in vegetarians: current knowledge and practical implications," American Journal of Clinical Nutrition, Vol. 78, No. 3, 640S-646S, September 2003.

(Emken, 1994) Emken EA, Adlof RO, Gulley RM, "Dietary linoleic acid influences desaturation and acylation of deuterium-labeled linoleic and linolenic acids in young adult males," Biochim Biophys Acta. 1994 Aug 4;1213(3):277-88.

(Horrobin, 1981) Horrobin, DF. "Loss of delta-6-desaturase activity as a key factor in aging." Med Hypotheses 1981;7:1211–20.

(Raederstorff, 1992) D. Raederstorff and U. Moser, “Influence of an increased intake of linoleic acid on the incorporation of dietary (n − 3) fatty acids in phospholipids and on prostanoid synthesis in rat tissues,” Biochimica et Biophysica Acta (BBA) - Lipids and Lipid Metabolism, Volume 1165, Issue 2, 2 December 1992, Pages 194-200.

(Undurti, 2008) Undurti, N Das, "Can essential fatty acids reduce the burden of disease(s)?" Lipids in Health and Disease 2008, 7:9

Chapter 12: Eicosanoids—cellular activists

Summary

Eicosanoids exert a fine control on our immune system, blood clotting, inflammation, and many other vital body systems. Their brief, but powerful effects last from seconds to minutes. Eicosanoids act locally on nearby cells only. They are not stored, but are made upon demand from precursors stored in cell membranes. We can influence these precursors and the resultant eicosanoids by varying the proportion of omega-6 and omega-3 fatty acids in our diet.

Eicosanoids are involved in pain and inflammation. Pharmaceutical drugs to control pain and inflammation include aspirin, ibuprofen, and COX-2 inhibitors. Aspirin and ibuprofen suppress pain and inflammation, but also increase the risk of stomach ulcers. The newer COX-2 inhibitors also suppress inflammation and pain, but with an increased risk of heart attacks.

Delicate interactions between different eicosanoids control blood clotting around injured arteries and areas of plaque. Thromboxanes and prostacyclins are eicosanoids involved in controlling blood clotting. Increased omega-3 from fish oils in the diet can reduce chances of fatal blood clots in people with advanced atherosclerosis. Unwanted side effects of increased omega-3 fatty acids include increased bleeding tendencies and reduced immune response to infection and tumors.

Eicosanoids called leukotrienes powerfully influence asthma and bronchitis. The wrong balance of leukotrienes can cause constriction and increased mucus accumulation in the small airways of the lungs. Plant sources of omega-3 fatty acids can give relief from asthma and bronchitis by altering the leukotrienes produced.

Prostaglandins are eicosanoids originally found in the prostate gland. There are many prostaglandins that interact together for fine control of inflammation, pain, fever, and blood clotting.

Eicosanoid precursors

The two essential fatty acids are ALA (alpha-linolenic acid) and LA (linoleic acid). Inside our bodies, they can be elongated and desaturated to become the three eicosanoid precursors. These three eicosanoid precursors are EPA (eicosapentaoic acid), arachidonic acid, and dihomo-gamma-linolenic acid (DGLA). Two of these three eicosanoids precursors can also be obtained from the diet. EPA can be found in some fatty fish and arachidonic acid can be found in livestock products. From these three eicosanoid precursors, our bodies can make all of the eicosanoids. For this chapter, please remember the abbreviation EPA. Other abbreviations will be mentioned to assist you in reading technical literature.

Eicosanoids

Eicosanoids are powerful signaling molecules that control inflammation, immunity, and other systems. They are also important in controlling blood clotting. The network of eicosanoid interactions is among the most complex in the human body.

The eicosanoids made from the omega-6 arachidonic acid are, in general, more powerful than either the eicosanoids made from the omega-3 EPA or the eicosanoids made from the omega-6 dihomo-gamma-linolenic acid, DGLA. The eicosanoids made from either EPA or DGLA are milder in effect and act as quenchers of the more powerful eicosanoids made from arachidonic acid.

Eicosanoids are not stored in the body. They are made upon demand when they are needed. They are made from eicosanoid precursors stored in cell membranes. These eicosanoid precursors are stored in phospholipids in cell membranes. Phospholipids can store two fatty acids. They prefer to store eicosanoid precursors in the "2" position.

Dietary consumption of the essential fatty acids LA and ALA affects the eicosanoid precursors stored in membrane phospholipids. Dietary arachidonic acid and EPA more powerfully affect the composition of the membrane phospholipids. The biosynthesis of eicosanoids is triggered by tissue damage or by the immune system.

Eicosanoids have a short half-life of seconds to minutes. They act on the same cells that they are made in (autocrine signalling), or on surrounding cells (paracrine signalling).

Figure 101 Types of Eicosanoids

Text Box: Types of Eicosanoids
Thromboxanes are made in blood platelets and influence blood clotting.
Leucotrienes are made in white blood cells and influence the immune system.
Prostacyclins inhibit blood clotting and open the blood vessels.
Prostaglandins influence the blood vessels, stomach, and more.

Eicosanoids in inflammation

Acute inflammation is characterized by redness, swelling, pain, and heat. Eicosanoids are involved in every aspect of these inflammatory reactions. Certain eicosanoids are vasodilators. These vasodilators open up tiny blood vessels resulting in redness. Other eicosanoids make tiny blood vessels more permeable. Plasma leaks out of these blood vessels and causes tissue swelling. Elevated levels of another eicosanoid sensitizes nerves, causing pain. This eicosanoid (prostaglandin E₂) can cause localized heat and systemic fever. Aspirin and NSAID (non-steroidal anti-inflammatory drugs) pain medications work by blocking the creation of certain eicosanoids.

A bee sting is an example of eicosanoid action. Immediately after the bee sting, certain eicosanoids briefly constrict capillaries to produce pale skin. Other eicosanoids open capillaries to produce redness. Next, eicosanoids control the swelling and pain. The sting may get hot from eicosanoid action. Later, other eicosanoids cool and calm the inflammation. In this example, the eicosanoids are activated by an injury. They act locally and temporarily. If there is a lack of alpha-linolenic acid in the diet or an imbalance in the linoleic/alpha-linolenic acid ratio, the local eicosanoids may cause too much inflammation. Direct intake of arachidonic acid from animal products will also affect this balance. Excessive inflammation can be due to an excess of arachidonic acid in cell membranes. On the other hand, if cell membranes are overloaded with EPA from dietary fish or fish oils, this inflammatory action may be reduced too much.

The eicosanoids

Let's take a closer look at the four classes of eicosanoids. The four classes are thromboxanes, leukotrienes, prostacyclins, and prostaglandins. All except leukotrienes are in the subclass called prostanoids.

Thromboxanes

There are two classes of thromboxanes, one made from arachidonic acid and the other made from EPA. Thromboxanes are found in blood platelets and are one of the types of eicosanoids that influence clotting. Thromboxanes were named after thrombocytes. Thrombocyte is another word for platelet. As you may know, platelets are involved in blood clotting.

Thromboxanes are mainly synthesized in platelets. Thromboxane production is enhanced during platelet activation. Platelets do not have COX-2 (cyclo-oxygenase 2), so they use COX-1 to create thromboxane from eicosanoid precursors. Thromboxanes are estimated to have a half-life of only 20-30 seconds.

Figure 102 Eicosanoid creation diagram

The Balance between series 2 and series 3 thromboxanes

The series numbers in the figure above refer to the number of double bonds in the eicosanoids. Series 2 eicosanoids have two double bonds and series 3 eicosanoids have three double bonds.

As you can see in the above figure, the series 3 thromboxanes are made from the omega-3 EPA. Also in the figure above are the series 2 thromboxanes. The series 2 thromboxanes are made from the omega-6 arachidonic acid. Both types of thromboxanes are made with cyclo-oxygenase enzymes.

The series 2 thromboxanes increase blood clotting, while the series 3 thromboxanes decrease blood clotting. In addition, the series 2 thromboxanes constrict arteries, while the series 3 thromboxanes open up arteries. The balance between these two thromboxanes is crucial for keeping arteries open while still responding to arterial damage.

The balance between the two classes of thromboxanes is influenced by the balance between dietary omega-3 and omega-6 fatty acids. In the typical American diet, the dietary omega-6 essential fatty acid linolenic acid is 10 to 20 times higher than the omega-3 essential fatty acid alpha-linolenic acid. In addition, dietary arachidonic acid from livestock products alters the balance between arachidonic acid and EPA. This predisposes some people to heart attacks and strokes.

Figure 103 The biosynthesis of thromboxane from arachidonic acid

The biosynthesis of thromboxanes

The biosynthesis of thromboxane from arachidonic acid is shown above. Arachidonic acid is extracted from a phospholipid in a cell membrane with the enzyme phospholipase. Arachidonic acid is transformed into prostaglandin H₂ (PGH₂) by cyclo-oxygenase (COX) and peroxidase enzymes. Thromboxane is synthesized from PGH₂ with an enzyme appropriately named thromboxane synthase. The resulting thromboxane is called thromboxane A₂ or TXA₂. A similar process creates thromboxane A₃ (TXA₃) from EPA.

Leukotrienes

Leukotrienes are eicosanoids made in white blood cells that influence and regulate some aspects of the immune response. Leukotrienes are formed in several types of immune system cells including mast cells, neutrophils, macrophages, and basophils. Leukotrienes act locally, either in the same cell that they were produced in (autocrine), or in adjacent cells (paracrine). Leukotrienes are well known for their role in contributing to inflammation in asthma and bronchitis.

Biosynthesis of Leukotrienes

Leukotrienes are either produced from EPA or from arachidonic acid in white blood cells. The first step in the creation of leukotrienes is the creation of HPETE (5-HydroPeroxyEicosaTetraEnoic Acid) by the action of the enzyme lipoxygenase. This is shown for arachidonic acid in the figure above.

Several types of leukotrienes are formed and labeled A, B, C, D, and E. The A series break down rapidly to the B series. The C, D, and E series have similar effects, but are slower acting. They can be triggered by anaphylactic shock. We will consider the B series made from arachidonic acid below called Leukotriene B₄ (LTB₄).

The leukotrienes made from arachidonic acid have four double bonds and so are in the "four" series. The leukotrienes made from EPA have five double bonds and so are in the "five" series. Leukotrienes of the four series are much more powerful than those in the five series.

Asthma and leukotrienes

When leukotrienes of the four series predominate, asthma and bronchitis can be worsened. There is increased secretion of mucus and more mucus accumulation in the lungs and airways. The air passages of the lungs become more constricted. Inflammation of the lining of the airways is made worse. Supplementation with oils rich in alpha-linolenic acid have been shown to ease the symptoms of asthma by increasing the five series of leukotrienes and by decreasing the four series of leukotrienes (Okamoto, 2000). It is interesting that supplementation with fish oils have not been shown to be of benefit in asthma, despite their high EPA content.

Inflammation and leukotrienes

Leukotriene B₄ (LTB₄) attracts neutrophils, which are the most numerous type of white blood cells. Neutrophils react within one hour of an injury. Leukotriene B₄attracts neutrophils through the bloodstream towards the site of the injury. Leukotriene B₄then attracts neutrophils out of the bloodstream into the damaged tissue. Leukotrienes help the blood vessels near an injury become more permeable. This allows neutrophils to leak out of the blood vessels. The release of leukotrienes is often accompanied with the release of histamine. Histamine assists in triggering the inflammatory response.

Figure 104 Inflammation triggered by leukotrienes

Text Box: Inflammation triggered by leukotrienes
Within one hour of an injury:
Leukotriene B4 attracts neutrophils through the bloodstream towards the site of the injury. Leukotriene B4 then attracts neutrophils out of the bloodstream into the damaged tissue.
Leukotrienes help the blood vessels near an injury become more permeable.
This allows neutrophils to leak out of the blood vessels.
The release of leukotrienes is often accompanied with the release of histamine.
Histamine assists in triggering the inflammatory response.

A healthy ratio of linoleic acid to alpha-linolenic acid reduces inflammation by altering leukotrienes. The healthiest ratio is from 2 to 1 to 4 to 1. Reducing arachidonic acid intake by avoiding livestock products also lowers inflammation, since the most inflammatory leukotrienes are made from arachidonic acid.

Figure 105 Biosynthesis of prostacyclin

Prostacyclins

Prostacyclins are made from prostaglandin H₂(PGH₂). Prostaglandin H₂ is made from arachidonic acid, as shown in the figure above. Series 2 prostacyclins are also known as prostaglandin I₂ and have the abbreviation PGI_2.There is an similar omega-3 eicosanoid labeled PGI₃. The unqualified term prostacyclin refers to PGI₂. It is interesting that prostacyclins in the omega-6 family act more like omega-3 eicosanoids. While the thromboxanes made from the omega-6 arachidonic acid increase blood clotting, prostacyclins powerfully inhibit blood clotting. Prostacyclins are 30 times more potent than other eicosanoid anti-clotting agents (Kelton,1980). Prostacyclins made from EPA (PGI₃) are also potent vasodilators. Prostacyclins have a half-life of only seconds to minutes.

Figure 106 Actions of prostacyclin

Text Box: Prostacyclin prevents the formation of a platelet plug in blood clot formation.
Prostacyclin is also a vasodilator, opening up blood vessels.
Prostacyclin opposes the action of series 2 thromboxanes.

Blood clotting and prostacyclins

Prostacyclin (PGI₂) is made by endothelial cells that line the inside of arteries. Prostacyclin functions by signaling nearby platelets and endothelial cells. Platelets and endothelial cells have receptors for prostacyclin. Once the prostacyclin receptor has been activated, platelet activation is inhibited, thus inhibiting blood clotting. Prostacyclin also counteracts any increase in platelet calcium levels caused by thromboxane A₂. Increased calcium levels in platelets increase coagulation of blood.

When prostacyclin binds to endothelial cells, it promotes smooth muscle relaxation and vasodilation. Together, prostacyclins and series 2 thromboxanes balance blood clotting and vasoconstriction.

Kidneys and prostacyclin

Prostacyclins have two roles in kidney function. PGI₂increases potassium secretion from the kidneys. In addition, PGI₂ with its well-known artery-opening properties increases kidney blood flow and urine flow.

Figure 107 Prostacyclin, thromboxane, and NSAIDs

Aspirin, Prostacyclin, and Thromboxane

The production of prostacyclin is inhibited by aspirin, ibuprofen, and other NSAID (non-steroidal anti-inflammatory drugs). If you look at the above figure, you will see that series 2 prostaglandins are made from arachidonic acid with the cyclooxygenase enzymes COX-1 and COX-2. The main cyclo-oxygenase enzyme for prostacyclin production is COX-2. NSAIDS inactivate the COX enzymes and so inhibit the production of series 2 thromboxanes and also series 2 prostacyclins.

The balance between thromboxanes and prostacyclins is important in preventing blood clots and atherosclerotic plaque buildup. Atherosclerotic lesions have an increased ability to produce receptors for thromboxane. It is evident that the correct balance between these two prostanoids is essential to good cardiovascular health and the prevention of heart attacks. The ratio of the two seems to be more important than the absolute amounts. COX-2 inhibitors like Vioxx may have increased blood clots by inhibiting prostacyclin synthesis relative to that of thromboxanes. Dietary omega-3 fatty acids seem to increase the anti-clotting prostacyclins in relation to the pro-clotting thromboxanes.

Aspirin and NSAIDS inhibit both prostacyclins and series 2 thromboxanes. Since series 2 thromboxanes promote blood clotting and prostacyclins inhibit blood clotting, it would seem that there would be no effect on clotting since they are both inhibited.

Initially there is little effect on blood clotting. Over time, though, the COX enzymes in endothelial cells regenerate faster. Prostacyclins are principally made by endothelial cells. Endothelial cells can make more COX enzymes because they are whole cells with a nucleus. Once the COX enzymes are regenerated in the endothelial cells, prostacyclin production can continue.

Series 2 thromboxanes are principally made by platelets. Platelets have no nucleus, and so, they cannot quickly regenerate COX enzymes. Thromboxane production cannot continue until new platelets are formed (Millwood, 2007). The half-life of a platelet is about four days, so it takes several days for platelets to be replaced. This leads to more prostacyclins and less of the series 2 thromboxanes—and thus less clotting.

At low doses, about 80 mg, aspirin exerts its most inflammatory effects. At these low doses, aspirin can trigger the synthesis of lipoxins. Lipoxins (abbreviated LX) are anti-inflammatory eicosanoids-like signaling molecules. Lipoxins are not classed as eicosanoids, but are similar. Lipoxins inhibit the inflammatory action of leukotrienes. Note that only aspirin and not other NSAIDS increase the generation of lipoxins.

Aspirin inactivates the COX enzymes, changing the balance between protacyclins and thromboxanes to favor the anti-clotting prostacyclins. This, in addition to the creation of anti-inflammatory lipoxins, is how aspirin works to decrease blood clotting. The reduction of clotting has a side effect of an increased tendency to bleed.

Figure 108 Prostaglandins and their formation

Prostaglandins

Prostaglandins are eicosanoids. The prostaglandins together with the thromboxanes and prostacyclins form the prostanoid subclass of eicosanoids. Of the eicosanoids, only the leukotrienes are left out of the prostanoid subclass. The name prostaglandin came from a Swedish researcher who discovered the substance in the prostate gland in 1935. It was not until the late part of the 20th century that chemists were able to understand and synthesize prostaglandins. Inside our bodies prostaglandins are synthesized from the two essential fatty acids or directly from arachidonic acid or EPA.

Prostaglandins are produced by nearly all of the cells of the body. Like the other eicosanoids, they act on the same cell that they are produced in or on nearby cells. Prostaglandins are thought to require transporters to cross cell membranes. When prostaglandins enter the circulation, they are quickly broken down and cleared by the kidneys. Prostaglandins in general are abbreviated as PG.

Prostaglandins are notorious for their control of pain, fever, inflammation, and blood clotting. Prostaglandins are also needed to regulate female reproduction and menses. Prostaglandins are involved in the protection of the lining of the stomach from stomach acid. Prostaglandins are also active in the kidneys. For more than a century drugs have been developed to control prostaglandins.

Figure 109 Series 1, 2, and 3 prostaglandins

Biosynthesis of prostaglandins

The most powerful prostaglandins are made from arachidonic acid and are in the 2 series. The number 2 in the description of a prostaglandin indicates the number of double bonds and it also helps us understand the precursor. The common precursor of all prostaglandins in the "2" series is called PGH₂. PGH₂is made from arachidonic acid, an omega-6. The most active prostaglandins are PGD₂, PGE₂, PGJ₂ and PGF₂_α. Corresponding prostaglandins are made from the omega-3 EPA (series 3) and dihomo-gamma-linolenic acid (DGLA) (series 1). DGLA is in the omega-6 family of fatty acids.

The enzyme that converts EPA, arachidonic acid, or DGLA into prostaglandins is cyclo-oxygenase (COX), also called prostaglandin synthase. COX-1 and COX-2 are found in the stomach, blood vessels, and kidneys. COX-1 is constantly produced by all cells with nuclei for housekeeping functions. COX-2 is produced under certain conditions such as tissue damage or inflammation. COX-3 remains unconfirmed in its existence or actions, but is believed to influence headaches.

Dietary fatty acids and prostaglandins

The series 1 and series 3 prostaglandins exert a much weaker effect than do the series 2 prostaglandins made from arachidonic acid. When fish oil is included in the diet, the EPA in the fish oil competes for cyclo-oxygenase enzymes at the expense of arachidonic acid. This leads to less of the series 2 (stronger) prostaglandins being produced from arachidonic acid. Although more of the series 3 prostaglandins are produced, they are weaker in their effects. Similarly, evening primrose oil with its high amounts of gamma-linolenic acid creates high amounts of DGLA, which also competes for cyclo-oxygenase. This creates more of the weaker series 1 prostaglandins and less of the highly active series 2 prostaglandins. This is how fatty fish or high sources of gamma-linolenic acid reduce the effects of prostaglandins. Gamma-linolenic acid is found in high amounts in evening primrose oil and borage oil.

Regulation of prostaglandins

Series 2 prostaglandins are primarily regulated by the availability of arachidonic acid and COX enzymes. The quantity of each prostaglandin is also selectively controlled by the expression of genes that make the specific enzymes for biosynthesis of PGD₂, PGE₂, and PGF₂_α. For example, there are three forms of the synthase enzyme for PGE₂. One important form of PGE synthase is found in the microsome and is often coupled with COX-2 for sustained production of PGE₂.

The effects of prostaglandins are additionally controlled by the expression of specific receptors on cell membranes and organelle membranes. There are four possible receptors for PGE₂and two for PGD₂. Thromboxanes, prostacyclins, and PGF₂_α, each have one specialized receptor. These receptors are a type called G-protein-linked receptors.

Transport across membranes further influences the effects of prostaglandins. Prostaglandins were once thought to use diffusion to cross cell membranes. We now know that they use a prostaglandin transporter to enter cells. Prostaglandins use another transporter for release from cells, the multidrug resistance protein 4. Transport across cell membranes is altered by the dietary intake of saturated, trans, and polyunsaturated fatty acids. Saturated and trans fatty acids reduce signal transduction. Signal transduction is a translation of one kind of signal into another, such as when a prostaglandin stimulates the expression of a gene.

The master series-2 prostaglandin PGH₂is the common precursor for enzymatic creation of prostaglandins including PGD₂, PGE₂, PJE₂, and PGF₂_α.

Prostaglandin E, PGE

Understanding the effects of PGE₂ is especially difficult because any of four different cell membrane receptors can cause different reactions to PGE₂. For instance, PGE₂ will cause dilation of the bronchial airways when acting on some cells while causing constriction of the bronchial airways when acting on other cells. Another example is that PGE₂ can cause either relaxation or contraction of the smooth muscles of the gastrointestinal tract. Cells can express different receptors for PGE₂ for different effects.

Inflammation and PGE

PGE₂ can have both pro-inflammatory and anti-inflammatory effects. PGE₂ helps to initiate inflammatory reactions and it also helps to resolve inflammations. PGE₂ is well known to induce fever and enhance pain. However, PGE₂ can help resolve inflammations by suppressing lymphocyte proliferation. PGE₂ also can inhibit the production of inflammatory cytokines. Limiting inflammation in another way, PGE₂ limits production of pro-inflammatory leukotrienes by interfering with lipoxygenase.

Blood clotting and PGE

It is interesting to note that different omega-6 eicosanoids can cause opposing effects. PGE₂ can be produced in atherosclerotic plaques and then act on platelets to influence clotting. In larger amounts, PGE₂ can inhibit platelet aggregation and cause less blood clotting through the EP4 platelet receptor. On the other hand, in smaller amounts, PGE₂ can increase platelet aggregation when acting through the EP3 receptor (Heptinstall, 2008).

The omega-6 (Series 2) prostacyclins dilate blood vessels and inhibit platelet aggregation. This is in contrast to the action of series 2 thromboxanes, which are also made from omega-6 fatty acids. Series 2 thromboxanes constrict blood vessels and increase blood clotting. In arteries and veins, prostaglandin PGF₂_α exerts a thromboxane-like contractile response whereas PGE₂ induces a prostacyclin-like relaxation response.

Immune response and PGE

PGE₂ inhibits cellular and humoral immune system responses. Specifically, PGE₂ suppresses T-cell proliferation, lymphokine production, the generation of cytotoxic cells, and natural killer cell activity. In contrast, the series 4 leukotrienes, also made from arachidonic acid, can increase immune response by increasing cytokine production, lymphocyte proliferation, interleukin, and natural killer cell activity. Fish oil suppresses both PGE₂ and series 4 leukotrienes. Several studies have shown that the net result of fish oil supplementation is that the immune system is suppressed (Nelson, 1990). A 65% decrease in natural killer cell activity was noted in one study where EPA was injected (Fritsche, 1987). Natural killer cells suppress both tumor cells and viral cells.

Lungs and PGE

PGE₂ can have anti-inflammatory and anti-asthmatic effects in the lungs by activating the EP3 receptor. EP3 receptors are one of the four possible receptors for PGE₂. Remember that cell membrane receptors affect the action of prostaglandins. The role of PGD₂ is more complex, but it may be pro-inflammatory in the lungs.

Digestion and PGE

Both prostacyclin and PGE₂ are present throughout the digestive tract. They both have protective effects on the gastrointestinal mucosa. They reduce hydrochloric acid secretion from parietal cells, while increasing blood flow and stimulating the secretion of mucus. They are both made with the assistance of COX-1. Aspirin and other NSAIDS inactivate COX-1 and this is how they contribute to an increased risk of ulcers.

Other effects of PGE

PGE₂ is a potent stimulator of bone resorption. This is of importance in osteoporosis. The receptor responsible for this action of PGE₂ is EP4. Bone osteoblasts are sites of production of PGE₂ where the production is regulated by several cytokines including interleukin-1 (Suzawa, 2000).

PGE₂ assists in the regulation of kidney function and flow. PGE₂ helps maintain the tone of the blood vessels in the kidney. PGE₂ also helps regulate salt and water excretion from the kidneys.

Eicosanoid	Receptor	Made in	Function
Prostaglandin PGH			Precursor to the other prostaglandins
Prostaglandin PGE	EP1	Stomach, Lungs	Contraction of GI tract smooth muscle and bronchoconstriction
Prostaglandin PGE	EP2	Stomach, Lungs	Relaxation of GI tract smooth muscle, vasodilation, and bronchodilation
Prostaglandin PGE	EP3	GI tract, Uterus	Less stomach acid secretion, increased mucus secretion, uterine contraction in pregnancy, contraction of GI tract smooth muscle,
Prostaglandin PGE	EP4	Osteoblasts	Bone resorption, promotes tumor growth
Prostaglandin PGE	Other	Systemic	Increased sensitivity to pain, fever, suppresses lymphocytes and immune response
Prostaglandin PGF	FP-PGF₂_α	Lungs, Heart , Spleen, Kidneys, Endometrium	Bronchoconstriction, uterine contraction, blood vessel contraction, labor
Prostaglandin PGD	DP1, DP2	Mast cells, CNS, Peripheral tissues	Tones down immune response, inflammation in allergies, resolution of inflammation, less blood clotting
Prostaglandin PGJ	Peroxisome proliferator-activated receptor	Activated T-cells	Inhibits tumor growth, anti-inflammatory regulator, immune regulator
Prostacyclin PGI	IP	Endothelium and Smooth muscle cells, Digestive tract	Inhibits platelet aggregation, vasodilation, and bronchodilation, pro-inflammatory, protect intestinal mucosa
Thromboxane TXA	TP	Platelets and lungs	Promotes platelet aggregation, vasoconstriction, smooth muscle proliferation, and may also be a pro-carcinogenic mediator
Leukotriene	CysLT and BLT	leukocytes, including mast cells, eosinophils, neutrophils, monocytes, and basophils.	Sustain inflammatory reactions in asthmatic and allergic reactions, powerful bronchoconstrictor, and increases vascular permeability.

Figure 110 Chart of eicosanoids and their functions

Prostaglandin D, PGD

Prostaglandin D (PGD) is mainly produced in mast cells. Mast cells release histamine and are involved in hypersensitivity reactions. PGD is made from PGH, which is made from one of the three eicosanoid precursors, usually arachidonic acid. PGD inhibits platelet and leukocyte aggregation, thus causing a thinning of blood. PGD is also a vasodilator.

PGD tones down the immune system by decreasing T-cell proliferation and lymphocyte migration. Interleukin production is inhibited by PGD as well. PGD may be pro-inflammatory in the lungs.

Prostaglandin F, PGF₂_α

PGF₂_α is mainly produced in the heart, spleen, and kidneys. PGF is produced from PGE, which is in turn produced from PGH. The 2-series of PGF is an indirect product of arachidonic acid, an omega-6 fatty acid. PGF₂_α increases vasoconstriction, bronchoconstriction, and smooth muscle contraction.

PGF is one of the main prostanoids made in the endometrium, and is involved in birth and menstruation. In the reproductive system, PGF₂_α and PGE₂ often exhibit opposite actions. PGF₂_α is a potent constrictor of uterine blood vessels. The biosynthesis of PGE₂ and PGF₂_α is increased appreciably during labor, and these prostaglandins are in fact used as drugs to induce labor.

Prostaglandin J, PGJ

The J-series of prostaglandins were once thought to be simply inactive degradation products of PGD. PGJ₂ is now well established as an anti-inflammatory regulator. PGJ₂ may also be involved in the immune response as it is produced in immune cells such as activated T lymphocytes. One type of PGJ₂ is important as an inhibitor of tumors.

PGJ and tumors

One form of PGJ (15-Deoxy-Δ^12,14-PGJ2) regulates the production of new growth of tumors (tumorigenesis). This PGJ prostaglandin inhibits tumor growth. It inhibits proliferation and stimulates cell death, apoptosis. It can also inhibit the migration of tumor cells. PGJ is opposed in its effects by PGE, which has opposite effects on proliferation, apoptosis, and migration of tumor cells using the cell receptor EP4 (Kundul, 2009). Thromboxane TXA₄ may also be a pro-cancer mediator.

References:

(Fritsche, 1987) Fritsche, I.T. and Johnston, P.V., "The effect of fish oil on prostaglandin production and natural killer cell activity in mice." 1987, Fed Proc. 46:1172

(Heptinstall, 2008) Stan Heptinstall, “DG-041 inhibits the EP3 prostanoid receptor—A new target for inhibition of platelet function in atherothrombotic disease,” Platelets; Dec., 2008, Vol. 19 Issue 8, p605-613, 9p, 5 charts.

(Kelton,1980) John G. Kelton,Morris A. Blajchman, "Prostaglandin I2 (prostacyclin)," CMA JOURNAL/JANUARY 26, 1980/VOL. 122

(Kundul, 2009) Namita Kundu, Xinrong Ma, Dawn Holt, Olga Goloubeva, Suzanne Ostrand-Rosenberg and Amy M. Fulton, "Antagonism of the prostaglandin E receptor EP4 inhibits metastasis and enhances NK function," Breast Cancer Research and Treatment, Volume 117, Number 2 , September, 2009

(Millwood, 2007) Charles L. Millwood, "New research on Aspirin and Health," p. 155, Nova Science Publishers, 2007.

(Nelson, 1990) Gary J. Nelson, "Health Effects of Dietary Fatty Acids." American Oil Chemists Society, Champaign, IL. 1990.

(Okamoto, 2000) Makoto, Okamoto, Fumihiro, Mitsunobu, Kozo, Ashida, Takashi, Mifune, Yasuhiro, Hosaki, Hirofumi, Tsugeno, Seishi, Harada and Yoshiro, Tanizaki, "Effects of Dietary Supplementation with n-3 Fatty Acids Compared with n-6 Fatty Acids on Bronchial Asthma." Internal Medicine, Vol.39, No.2(2000)pp.107-111.

(Suzawa, 2000) Tetsuo Suzawa, Chisato Miyaura, Masaki Inada, Takayuki Maruyama, Yukihiko Sugimoto, Fumitaka Ushikubi, Atsushi Ichikawa, Shuh Narumiya, and Tatsuo Suda, "The Role of Prostaglandin E Receptor Subtypes (EP1, EP2, EP3, and EP4) in Bone Resorption: An Analysis Using Specific Agonists for the Respective EPs," Endocrineology, Vol. 141, No. 4, 2000.