Trans fatty acids are found in very minor amounts, usually less than 2 percent but sometimes up to 5 percent of the total fat, in all naturally occurring ruminant fats (antelope, buffalo, cow, deer, goat and sheep). They are found in major amounts, as much as 50 to 60 percent or more of the total fat, in partially hydrogenated vegetable oils.[i]
Actually the kinds of trans fatty acids found in ruminant fats differ considerably from those found in partially hydrogenated vegetable oils because of the average placement of the trans double bonds. This form of trans fats found in ruminant animals is a precursor to conjugated linoleic acid (CLA), which is reported to be anticarcinogenic.[ii]
The major trans
fatty acids found in partially hydrogenated vegetable oils have the majority of
their double bonds in sites along the 18 carbon fatty acid that are found to
raise health problems. A French chemist named Sabatier first discovered the
technology by which liquid vegetable oils could be hardened to make margarine.
He found that a nickel catalyst would cause the hydrogenation-the addition of
hydrogen to unsaturated bonds to make them saturated-of ethylene gas to ethane.
Subsequently the British chemist Norman developed the first application of
hydrogenation to food oils and took out a patent. In 1909, Procter & Gamble
The hydrogenation process transforms unsaturated oils into straight "packable" molecules, by rearranging the hydrogen atoms at the double bonds. In nature, most double bonds occur in the cis configuration, that is with both hydrogen atoms on the same side of the carbon chain at the point of the double bond. It is the cis isomers of fatty acids that have a bend or kink at the double bond, preventing them from packing together easily. Hydrogenation creates trans double bonds by moving one hydrogen atom across to the other side of the carbon chain at the point of the double bond. In effect, the two hydrogen atoms then balance each other and the fatty acid straightens, creating a packable "plastic" fat with a much higher melting temperature.
Although trans fatty acids are technically unsaturated, they are configured in such a way that the benefits of unsaturation are lost. The presence of several unpaired electrons presented by contiguous hydrogen atoms in their cis form allows many vital chemical reactions to occur at the site of the double bond. When one hydrogen atom is moved to the other side of the fatty acid molecule during hydrogenation, the ability of living cells to make reactions at the site is compromised or altogether lost. Trans fatty acids are sufficiently similar to natural fats that the body readily incorporates them into the cell membrane; once there their altered chemical structure creates havoc with thousands of necessary chemical reactions-everything from energy provision to prostaglandin production.
After the Second World War, "improvements" made it possible to plasticize highly unsaturated oils from corn and soybeans. New catalysts allowed processors to "selectively hydrogenate" the kinds of fatty acids with three double bonds found in soy and canola oils. Called "partial hydrogenation," the new method allowed processors to replace cottonseed oil with more unsaturated corn and soybean oils in margarines and shortenings. This spurred a meteoric rise in soybean production, from virtually nothing in 1900 to 70 million tons in 1970, surpassing corn production. Today soy oil dominates the market and is used in almost eighty percent of all hydrogenated oils.
When people eat fats containing these forms of trans fatty acids, the fatty acids are deposited in varying amounts in some of the tissues. Trans fats from partially hydrogenated vegetable oils also can have a negative impact on the functioning of organs in the body. Trans fatty acids from partially hydrogenated vegetable oils disrupt cellular function, which affects enzyme functionality. These trans fats interfere with the necessary conversions of both the omega-6 and omega-3 essential fatty acids (EFA) to their elongated forms and consequently escalate the adverse effects of EFA deficiency (see next section on essential fatty acids).
Most of the trans isomers in modern hydrogenated fats are new to the human physiology and by the early 1970's a number of researchers had expressed concern about their presence in the American diet, noting that their increasing use had paralleled the increase in both heart disease and cancer.[iii] In fact, as early as 1958 Ancel Keys originally claimed that partially hydrogenated vegetable oils with their trans fatty acids were the culprits in heart disease, not saturated fats.[iv]
Most of the trans fats in the current American diet come not from margarine but from shortening used in fried and processed foods. American shortening consumption of 10 grams per person per day held steady until the 1960's, although the content of that shortening had changed from mostly lard, tallow and coconut oil-all natural fats-to partially hydrogenated soybean oil. Then shortening consumption shot up and by 1993 had tripled to over 30 grams per person per day.[v]
The particular mix of fatty acids in soy oil results in shortenings containing about 40% trans fats, an increase of about 5% over cottonseed oil, and 15% over corn oil. Canola oil, processed from a hybrid form of rape seed, is particularly rich in fatty acids containing three double bonds and the shortening can contain as much as 50% trans fats. Trans fats of a particularly problematical form are also formed during the deodorization of canola oil, although they are not indicated on labels for the liquid oil.[vi]
Approximately 70 percent of all the vegetable oils used in processed foods such as crackers, cookies, pastries, cakes, and fried foods are partially hydrogenated and therefore contain high levels of trans fats.[vii] The commercial shortenings used in these products have 25-50 percent of the fat as trans fats; commercial shortenings made with partially hydrogenated canola oils have the same or even higher levels of trans fatty acids. This means that the fat ingredient in cookies, crackers, donuts, cakes, frostings, etc. is between one-quarter and one half trans fatty acids.[viii]
Trans fatty acids in the diet, created from partially hydrogenating vegetable oils, have been implicated as causing or exacerbating most of our modern diseases, including heart disease, cancer, diabetes, obesity, immune dysfunction and bone loss. Some adverse effects of consuming trans fatty acids reported in humans and animals are the following:
· increases blood insulin levels in humans in response to glucose load, increasing risk for diabetes;
· interfere with the ability of new mothers to nurse successfully and increase the likelihood of developing diabetes (lowers the amount of cream by volume in milk from lactating females in all species studied, including humans, thus lowering the overall quality available to an infant);
· predispose pregnant mothers to low-birth-weight babies;
· causes a dose response decrease in visual acuity in infants who are fed human milk with increasing levels of trans fatty acids, which extends to 14 months of age;
· affects immune response by lowering efficiency of B cell response and increasing proliferation of T cells;
· decreases the response of the red blood cell to insulin, thus having a potentially undesirable effect on diabetes;
· causes alterations in adipose cell size, cell number, lipid class, and fatty acid composition;
· contributes to osteoporosis;
· decreases testosterone, causes the production of abnormal sperm and altered gestation;
· causes adverse alterations in the activities of the important enzyme system that metabolizes chemical carcinogens and drugs;
· precipitates childhood asthma;
· interferes with the body's use of omega-3 fatty acids found in fish oils, grains and green vegetables, leading to impaired prostaglandin production;
· increases the incidence of heart disease because trans fatty acids lower HDL cholesterol, increase LDL and increase the heart disease marker Lipoprotein [a] (Lp[a]) while saturated fats lower Lp[a};
· raises total serum cholesterol levels 20-30mg%; and
· causes adverse alterations in physiological properties of biological membranes including measurements of membrane transport and membrane fluidity.
(Table derived from Mary Enig, PhD, Trans Fatty Acids in the Food Supply: A Comprehensive Report Covering 60 Years of Research, 2nd Edition, Bethesda Press, 1995 and Mary Enig, Know Your Fats: The Complete Primer for Understanding the Nutrition of Fats, Oils and Cholesterol, Bethesda Press, 2000, pp 42-44 and 85-86).
The Foundation is pleased with the recent FDA ruling requiring food labels to incorporate information on trans fatty acid content by 2006.[ix] However, we wish to make it very clear that trans fatty acids are not natural saturated fats and should not be considered as such. Many researchers, health organizations and food companies tend to lump saturated fats and trans fatty acids together as the same, particularly for food labeling purposes. This is a grave mistake that has contributed to incorrectly associating beneficial saturated fatty acids with the negative health implications of trans fatty acids.
However, the Foundation does not support the National Academy of Science Institute of Medicine's (IOM) recent advisory that nutrition labeling for foods list a combined Daily Value (DV) for saturated and trans fatty acids. The IOM ostensibly included this recommendation "so consumers will know that both contribute to cardiac health risk."[x] The IOM said that a combined DV for saturated and trans fat would help educate the consumer that, although the two components are chemically different, "neither is desirable in terms of [cardiac health risk]." The Foundation finds this advisory to be ill-advised and ill-considered, considering the negative health implications of trans fatty acids and the healthful aspects of saturated fats.
[i] Enig, Know Your Fats: The Complete Primer for Understanding the Nutrition of Fats, Oils and Cholesterol, Bethesda Press, 2000, pp. 38-39.
[ii] Chin et al, Dietary Sources of conjugated Linoleic Isomers of Linoleic Acid, a Newly recognized Class of Anticarcinogens, Journal of Food Composition and Analysis, 1992, 5:185-197.
[iii] Enig, Oiling of America, http://www.westonaprice.org/know_your_fats/oiling.html, p. 6.
[iv] Enig, Know Your Fats, p. 85.
[v] Enig, Oiling of America, p. 21.
[vi] Researchers at the University of Florida at Gainsborough found trans levels as high as 4.6% in processed canola oil. (S. O'Keefe and others. Journal of Food Lipids1994;1:165-176.) The conversion of omega-3 fatty acids to trans fats can be prevented by certain careful processing methods. (JL Sebedio and others. European Journal of Clinical Nutrition 2000 Feb;54(2):104-13
[vii] Enig, Know Your Fats, p. 44.
[viii] Enig, Know Your Fats, pp. 38-45.
[ix] Food Labeling; Trans Fatty Acids in Nutrition Labeling; Consumer Research to Consider Nutrient Content and Health Claims and Possible Footnote or Disclosure Statements; Final Rule and Proposed Rule, Food and Drug Administration, Federal Register: July 11, 2003, volume 68, Number 133, pp 41433-41506. See also U.S. Office of Management and Budget, Letter to the Department of Health and Human Services regarding trans fatty acids, September 18, 2001.
[x] Food Chemical News, "IOM Advises Condensed daily Value for Saturated and Trans Fatty Acids," Vol. 45, No. 45, December 22, 2003.