Fats, oils, fatty acids...

Great educational material for anyone that wants to untangle cholesterol and fat questions. We appreciate greatly Antonio Zamora's kind permission to reprint his work here -- Dr. A. Kulisz

Lipids consist of numerous fatlike chemical compounds that are insoluble in water but soluble in organic solvents. Lipid compounds include monoglycerides, diglycerides, triglycerides, phosphatides, cerebrosides, sterols, terpenes, fatty alcohols, and fatty acids.

Fatty acids consist of the elements carbon (C), hydrogen (H) and oxygen (O) arranged as a carbon chain skeleton with a carboxyl group (-COOH) at one end. Saturated fatty acids have all the hydrogen that the carbon atoms can hold, and therefore, have no double bonds between the carbons. Monounsaturated fatty acids have only one double bond. Polyunsaturated fatty acids have more than one double bond.

Butyric acid (butanoic acid) is one of the saturated short-chain fatty acids responsible for the characteristic flavor of butter. This image is a detailed structural formula explicitly showing four bonds for every carbon atom and can also be represented as the equivalent line formulas:

The numbers at the beginning of the scientific names indicate the locations of the double bonds. By convention, the carbon of the carboxyl group is carbon number one. Greek numeric prefixes such as di, tri, tetra, penta, hexa, etc., are used as multipliers and to describe the length of carbon chains containing more than four atoms. Thus, "9,12-octadecadienoic acid" indicates that there is an 18-carbon chain (octa deca) with two double bonds (di en) located at carbons 9 and 12, with carbon 1 constituting a carboxyl group (oic acid) . The structural formula corresponds to:

Fatty acids are frequently represented by a notation such as C18:2 that indicates that the fatty acid consists of an 18-carbon chain and 2 double bonds. Although this could refer to any of several possible fatty acid isomers with this chemical composition, it implies the naturally-occurring fatty acid with these characteristics, i.e., linoleic acid.

Double bonds bind carbon atoms tightly and prevent rotation of the carbon atoms along the bond axis. This gives rise to configurational isomers which are arrangements of atoms that can only be changed by breaking the bonds.

These three-dimensional molecular projections show the Cis and Trans configurational isomers of 9-octadecenoic acid with the hydrogen atoms shown in blue. The Latin prefixes Cis and Trans describe the orientation of the hydrogen atoms with respect to the double bond. Cis means "on the same side" and Trans means "across" or "on the other side". Naturally occurring fatty acids generally have the Cis configuration. The natural form of 9-octadecenoic acid (oleic acid) found in olive oil has a "V" shape due to the Cis configuration at position 9. The Trans configuration (elaidic acid) looks more like a straight line.

Omega-3 (ω3) and omega-6 (ω6) fatty acids are unsaturated "Essential Fatty Acids" (EFAs) that need to be included in the diet because the human metabolism cannot create them from other fatty acids. These fatty acids use the Greek alphabet (α,β,γ,...,ω) to identify the location of the double bonds. The "alpha" carbon is the carbon closest to the carboxyl group, and the "omega" is the last carbon of the chain because omega is the last letter of the Greek alphabet. Linoleic acid is an omega-6 fatty acid because it has a double bond six carbons away from the "omega" carbon. Similarly, alpha-linolenic acid is an omega-3 fatty acid because it has a double bond three carbons away from the "omega" carbon. By subtracting the highest double-bond locant in the scientific name from the number of carbons in the fatty acid we can obtain its classification. For arachidonic acid, we subtract 14 from 20 to obtain 6; therefore, it is an omega-6 fatty acid. This type of terminology is sometimes applied to oleic acid which is an omega-9 fatty acid.

In these simplified structural formulas of unsaturated fatty acids, each angle represents a carbon atom. Notice that all the double bonds have the Cis configuration. Omega-3 and omega-6 fatty acids are sometimes called n3 and n6 fatty acids.

DHA (docosahexaenoic acid) and AA (arachidonic acid) are both crucial to the optimal development of the brain and eyes. The importance of DHA and AA in infant nutrition is well established, and both substances are routinely added to infant formulas. An imbalance of omega-3 and omega-6 fatty acids may lead to a variety of mental disorders, including hyperactivity, depression, and schizophrenia. A balanced ratio of these two fatty acid families is necessary for a healthy brain.

Vegetable cooking oils and animal fats consist mainly of triglycerides. Triglycerides have lower densities than water (they float on water), and at normal room temperatures may be solid or liquid. When solid, they are called "fats" or "butters" and when liquid they are called "oils". Triglycerides are chemical compounds formed from one molecule of glycerol and three fatty acids.

Glycerol is a trihydric alcohol (containing three -OH hydroxyl groups) that can combine with up to three fatty acids to form monoglycerides, diglycerides, and triglycerides. Fatty acids may combine with any of the three hydroxyl groups to create a wide diversity of compounds. Monoglycerides, diglycerides, and triglycerides are classified as esters which are compounds created by the reaction between acids and alcohols that release water (H₂O) as a by-product.

The triglyceride structural formula on the left is typical of olive oil. It consists of two radicals of oleic acid and one of palmitic acid attached to glycerol (the vertical carbon chain). The small squares represent the fatty acid components of the glyceride molecules. The picture on the right shows the three-dimensional molecular structure of tristearin, a triglyceride with three stearic acid radicals. Oxygen atoms are shown in red, carbon atoms as dark gray, and hydrogen atoms as blue. Tristearin is found as a minor component in many natural fats.

Soap is made traditionally by heating an alkali like sodium hydroxide (NaOH) with animal fat. The chemical reaction (hydrolysis) produces glycerol and soap, which consists of the sodium salts of the fatty acids, e.g., sodium stearate (CH₃(CH₂)₁₆C(O)O^- Na⁺).

Diglycerides have two fatty acid radicals, whereas monoglycerides have only one fatty acid radical per molecule of glycerol.

All esters of glycerol and fatty acids are metabolized in the same way. Monoglycerides, diglycerides, and triglycerides all have 9 Calories per gram, but some nutrition labels hide the calories of mono- and diglycerides under the contention that "fat" consists only of triglycerides.

Fatty acid compositions depend on the sources of the oils. Canola oil is made from selectively bred rapeseed plants that contain less than 2% erucic acid. Some crops have produced canola oil with 76% oleic acid. Where percentages vary, average values are used. Not shown in this table: Coconut oil has 8% caprylic acid (C8:0). Cod liver oil has 7% palmitoleic acid (C16:1), 17% C20 unsaturated fatty acids (10% EPA), and 11% C22 unsaturated fatty acids (6% DHA). Peanut oil has approximately 5% of C22:0 and C24:0 fatty acids. Cow butterfat has 4% butyric (C4:0) and 2% caproic (C6:0) acids. Beef tallow, cow butterfat, human butterfat, and lard all have about 3% palmitoleic acid (C16:1). Human depot fat, usually found in the abdomen of men and around the thighs and hips of women, has a composition similar to lard.

What are the triglyceride profiles of these fats and oils? The percentages in the table above reflect the overall proportions of the fatty acid radicals in the triglycerides. If we had 33 representative triglyceride molecules containing 99 fatty acid radicals, the number of each fatty acid radical in these 33 molecules would be proportional to its percentage in the table. For example, 33 representative molecules of lard triglycerides would contain, on average, 26 radicals of palmitic acid (C16:0), 14 radicals of stearic acid (C18:0), 44 radicals of oleic acid (C18:1), and 10 radicals of linoleic acid (C18:2). These fatty acid radicals would be distributed randomly among the 33 triglyceride molecules. The typical lard triglyceride molecule would have one or two radicals of oleic acid and one radical of palmitic acid. Frequently, there would be triglycerides with one radical each of oleic, palmitic, and stearic acids. Only rarely would one encounter triglycerides with only palmitic and stearic acid radicals.

This profile was constructed using a random distribution of the appropriate percentages of the fatty acids in 33 representative triglyceride molecules. Red is used for saturated, green for monounsaturated, and blue for polyunsaturated fatty acids. Although the composition of the individual triglyceride molecules may vary, the relative proportion of fatty acids remains constant. The profiles for canola oil or olive oil would be mostly green and blue with very little red, whereas the profile for coconut oil would be mostly red.

Unsaturated fats exposed to air oxidize to create compounds that have rancid, stale, or unpleasant odors or flavors. Hydrogenation is a commercial chemical process to add more hydrogen to natural unsaturated fats to decrease the number of double bonds and retard or eliminate the potential for rancidity. Unsaturated oils, such as soybean oil, which contain unsaturated fatty acids like oleic and linoleic acid, are heated with metal catalysts in the presence of pressurized hydrogen gas. Hydrogen is incorporated into the fatty acid molecules and they become saturated with hydrogen. Oleic acid (C18:1) and linoleic acid (C18:2) are both converted to stearic acid (C18:0) when fully saturated. The liquid vegetable oil becomes a solid saturated fat (shortening with a large percentage of tristearin). By comparison, animal fats seldom have more than 70% saturated fatty acid radicals. In the table above, for example, lard has 54% unsaturated fatty acid radicals.

Fully saturated fats are too waxy and solid to use as food additives, so manufacturers use partially hydrogenated oils. These oils are also produced at high temperatures with metal catalysts and pressurized hydrogen, but the process is stopped when the oil has the proper consistency for its application. The high temperatures and catalysts used for this chemical reaction weaken the double bonds and, as a side effect, cause a large percentage of the natural Cis double bonds to change to Trans double bonds. Trans fatty acids are present mainly in partially hydrogenated fats, but they are also present in hydrogenated fats because chemical reactions never achieve 100% efficiency.

Metabolism of natural 20-carbon polyunsaturated fatty acids like arachidonic acid results in the biosynthesis of mediators with potent physiological effects such as prostaglandins, prostacyclins, thromboxanes, leucotrienes, and lipoxins. These substances are known collectively as eicosanoids because they contain 20 carbon atoms (Greek eikosi = 20). However, polyunsaturated trans fatty acids cannot be used to produce useful mediators because the molecules have unnatural shapes that are not recognized by enzymes such as cyclooxygenase and lipoxygenase. Some trans fatty acids occur naturally in low proportions in some foods, but they occur in large proportions in partially hydrogenated oils. When large amounts of Trans fatty acids are incorporated into the cells, the cell membranes and other cellular structures become malformed and do not function properly.

Trans fats are bad for your heart. Dietary trans fats raise the level of low-density lipoproteins (LDL or "bad cholesterol") increasing the risk of coronary heart disease. Trans fats also reduce high-density lipoproteins (HDL or "good cholesterol"), and raise levels of triglycerides in the blood. Both of these conditions are associated with insulin resistance which is linked to diabetes, hypertension, and cardiovascular disease. Harvard University researchers have reported that people who ate partially hydrogenated oils, which are high in Trans fats, had nearly twice the risk of heart attacks compared with those who did not consume hydrogenated oils. Because of the overwhelming scientific evidence linking Trans fats to cardiovascular diseases, the Food and Drug Administration will require all food labels to disclose the amount of Trans fat per serving, starting in 2006.

Trans fats are bad for your brain. Trans fats also have a detrimental effect on the brain and nervous system. Neural tissue consists mainly of lipids and fats. Myelin, the protective sheath that covers communicating neurons, is composed of 30% protein and 70% fat. Oleic acid and DHA are two of the principal fatty acids in myelin. Studies show that trans fatty acids in the diet get incorporated into brain cell membranes, including the myelin sheath that insulates neurons. These synthetic fats replace the natural DHA in the membrane, which affects the electrical activity of the neuron. Trans fatty acid molecules alter the ability of neurons to communicate and may cause neural degeneration and diminished mental performance. Neurodegenerative disorders such as Parkinson's and Alzheimer's appear to exhibit membrane loss of fatty acids. Unfortunately, our ingestion of trans fatty acids starts in infancy. A Canadian study showed that an average of 7.2% of the total fatty acids of human breast milk consisted of trans fatty acids which originated from the consumption of partially hydrogenated vegetable oils by the mothers.

Phospholipids or phosphatides are natural surfactants and emulsifiers consisting of an alcohol such as glycerol, one or two molecules of fatty acid, and a phosphoric acid compound. They are found in all plants and animals and include such substances as lecithin, cephalin, and sphingomyelin. Lecithin is a significant constituent of brain and nervous tissue consisting of a mixture of diglycerides of stearic, palmitic, and oleic acids, linked to the choline ester of phosphoric acid. The chemical structure of dipalmitoyl lecithin illustrated here is typical of the phosphatides found in the brain, lung, and spleen.

Sterols, such as cholesterol, are alcohols with the cyclopentanophenanthrene ring system (atoms 1 through 17 in the structure below). This substructure is also found in steroid hormones such as testosterone, progesterone, and cortisol. Cholesterol is considered an alcohol because it has a hydroxyl group (-OH) in position 3 of the ring system. Cholesterol is produced by the liver and is found in all body tissues where it helps to organize cell membranes and control their permeability. A high level of cholesterol in the blood is a risk factor for cardiovascular diseases. Cholesterol and lipoprotein levels can be normalized through exercise and reduced Calorie diets that are low in carbohydrates and eliminate hydrogenated fats.

Sterols of vegetable origin are called "phytosterols". They have the same basic structure as cholesterol, but differ in the side chains attached to carbon 17. Phytosterols, such as stigmasterol from soybean oil, are of current interest because they lower blood cholesterol levels. Sterols that are fully saturated (no double bonds) are called "stanols". For example, stigmastanol has the same structure as stigmasterol, but without the double bonds. When fatty acids react with the hydroxyl at carbon 3 they form "sterol esters".

The production of edible fats is a large commercial enterprise worth millions of Dollars that involves many segments of our society, including farmers who cultivate oil-bearing plants, ranchers and fishermen who provide sources of animal fats, and a variety of industries that extract, process, store, and distribute the resulting fats and oils. There is a constant tug-of-war between manufacturers, consumers, special interest groups, and government regulatory agencies, each trying to advance their own agenda. Fats and sugars have been blamed for the epidemic increase of obesity during the last thirty years, and well-intentioned government agencies and public advocacy groups have influenced official policy decisions, but not always based on a sound scientific foundation because it takes many years to determine the health consequences of specific products or policies. Many times, policies are enacted for political reasons to benefit farmers and manufacturers at the expense of public health.

Hydrogenated fats
By now, it is a well-established fact that trans fats are harmful and are responsible for causing thousands of deaths per year from cardiovascular diseases, but hydrogenated fats continue to be added to so many food products that it almost impossible to avoid them. Frequently, even lard is hydrogenated! Why aren't these products banned? Because manufacturers with a lot of political influence don't want to lose money on products that might turn rancid before they are sold. Fast modern distribution methods, good packaging, and controlled temperature storage could solve this problem and deliver healthier products to the consumers, but it would increase costs. One of the latest trends used by manufacturers is to avoid the word "hydrogenated" and to obtain oils from foreign sources where our regulations do not apply. Some products use "Modified Palm Oil" without mentioning the process used to modify the oil. The modification could be a simple fractionation to separate high-melting from low-melting triglycerides, but it could involve hydrogenation.

The Fat Free Craze
The concept that some fats are essential for good health is just emerging in the awareness of the general public, but the aversion to fat resulting from many years of indoctrination against fat has resulted in great consumer demand for low fat or nonfat products. Some manufacturers, eager to increase their sales, concoct "Fat Free" products that use monoglycerides and diglycerides instead of triglycerides. Average consumers, not knowing the difference, eat these products under the illusion that they are low in calories because the manufacturers do not disclose in the Nutrition Facts the calories, or whether the constituent fatty acids of the mono- and diglycerides are saturated or hydrogenated. New regulations are often adopted as a reaction to abuses like this, but it is a slow process that may be further delayed by lobbying and enables manufacturers to continue reaping profits in the meantime.

Saturated Fats
For many years, saturated fats were equated with the "artery clogging" deleterious health effects associated with trans fats. Many authoritative medical sources still advise decreasing the consumption of saturated fats to reduce the risk of cardiovascular diseases. While this advice may be valid under some circumstances, several scientific studies indicate that saturated fats have beneficial biological effects and differ significantly from trans fats which are always bad. It is worthwhile noting that the butterfat in human milk has 20% more saturated fats than lard. Saturated fatty acids, particularly medium chain fatty acids such as lauric and capric acids, have been found to play an important role in supporting the immune system. These findings put the highly saturated and much maligned coconut and palm kernel oils in a more favorable light. We are not likely to see these oils in our grocery shelves any time soon since they must be imported from tropical countries to compete with products from regional farmers, and we would have to overcome our deeply ingrained fear of saturated fats. Promoting tropical oils for their health benefits is not going to be politically popular.

Our knowledge of the metabolism of fats continues to increase and it will take many years of research and expensive long-term studies to establish objective facts to clarify the conflicting statements from government agencies, short-term studies, advocacy groups, commercial interests, and the latest diet fads. If you are confused about what fats to eat because of the barrage of advertisements, inflammatory language, and misinformation, here is some simple advice: consume unaltered natural oils and fats that have been used traditionally for hundreds or thousands of years, and avoid oils that have been chemically modified or created in a laboratory. If your weight is in the normal range, animal fats such as lard can be used to meet a portion of your caloric needs, as long as the lard originates from organically raised animals and it is not hydrogenated. Many pesticides used in farms concentrate in fatty tissues and can result in high pesticide residues in fat from animals that are not raised organically.

References

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Booyens J, Louwrens CC, Katzeff IE. The role of unnatural dietary trans and cis unsaturated fatty acids in the epidemiology of coronary artery disease. Med Hypotheses 1988; 25:175-182.
Mensink RPM, Katan MB. Effect of dietary trans fatty acids on high-density and low-density lipoprotein cholesterol levels in healthy subjects. N Engl J Med 1990; 323:439-45.
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Mary G. Enig, Trans Fatty Acids in the Food Supply: A Comprehensive Report Covering 60 Years of Research , 2nd Edition, 1995, Enig Associates, Inc., Silver Spring, MD
Ben Best, Fats You Need -- Essential Fatty Acids. An overview of fats, their metabolism, and their roles in improving health.
The Institute of Shortening and Edible Oils. http://www.iseo.org/ Chemical information about fats from the point of view of refiners of edible fats and oils in the United States.
Claude Leray, Cyberlipid Center Description of lipids, their properties, methods of analysis, bibliographic references, and historical notes.
Handbook of Chemistry and Physics. 74th Edition, 1993-1994, Fats and Oils, p. 7-29.
Grandgirard A, Bourre JM, Julliard F, Homayoun P, Dumont O, Piciotti M, Sebedio JL, Incorporation of trans long-chain n-3 polyunsaturated fatty acids in rat brain structures and retina. Lipids, 1994 April; 29(4):251-8.
Ratnayake WM, Chen ZY, Trans, n-3, and n-6 fatty acids in Canadian human milk. Lipids, 1996 March; 31 Suppl:S279-82.
Renner, E., Milk and Milk Products in Human Nutrition. Volkswirtsch. Verlag, Munich, 467 pp., 1982.
Mary G. Enig, Coconut: In Support of Good Health in the 21st Century, 36th meeting of APCC, 1999.

Fatty Acid Configurations -- What are Trans Fats?

What are Omega-3 and Omega-6 fatty acids?

Fats and Oils -- What are Triglycerides?

Common Fatty Acids

Fatty Acid Configurations

What are Trans Fats?

What are Omega-3 and Omega-6 fatty acids?

Fats and Oils

What are triglycerides?

Fatty acid composition of some common edible fats and oils.

What is Hydrogenation and Partial Hydrogenation?

Metabolism of Fats -- Why are Trans Fats Bad?

Phospholipids/Phosphatides

Sterols

The Politics of Fats

References