Transforming Perceptions
About Trans Fatty Acids
June 1998 -- Nutrition Notes

By: Andrea Platzman, R.D.
Contributing Editor

  Once considered benign saturated-fat substitutes, trans fatty acids suddenly don't seem to be all they were cracked up to be.  "Experiments conducted in the 1960s showed that trans fatty acids added to human diets were cholesterol-neutral - that is, they neither raised nor lowered serum cholesterol," says John Allred, Ph.D., professor of nutrition, department of food science and technology, Ohio State University, Columbus. "In more recent studies, trans fatty acids were added in place of the normal cis forms, and serum cholesterol levels were shown to rise. Taken together, the two types of studies show that it is the removal of cis, not the addition of trans, which raises serum cholesterol." And with the rise in the use of hydrogenated oils to replace saturates (animal fats and tropical oils), this is exactly what has happened. Estimates of the trans fatty acid consumed in the U.S. range from approximately 5% to 8% of the total calories consumed in the average American's diet.  In one way, trans fatty acids might prove even worse than saturated fat, according to a 1994 study by Dr. Joseph Judd, researcher at USDA's Agricultural Research Service's Human Nutrition Research Center, Beltsville, MD. Trans fatty acids increase low-density lipoprotein (LDL), known as "bad" cholesterol. They also seem to lower high-density lipoprotein (HDL), the "good" cholesterol (which saturated fat leaves untouched). In addition, trans fatty acids also might negatively affect lipoprotein levels in the blood, a hereditary risk factor for heart disease, and might be a risk factor in tumorgenesis. Judd is currently working on a new study concerning the effect of trans fatty acids and saturated fatty acids on blood lipids and lipoproteins.Transformation  Fats contains three fatty acids. The types of fatty acids play an important role since chain length and the carbon linkages influence how a fat affects the body.  When the carbons are linked by a double bond, or unsaturated, they are prone to oxidation and tend to produce a lower melting point. When a fatty acid is saturated, it means there is a single bond with attached hydrogen ions. In naturally occurring bonds, these are arranged in the cis configuration, where both hydrogen atoms are on the same side of the carbon atoms. Hydrogenation forms molecules configured in a different shape, called trans. This increases oil stability and mimics the functionality of the saturated animal fats. Anywhere from 7% to 30% of margarine is comprised of trans fatty acids.  "Margarine is not simply a cube of trans fat," says Christina Stark, M.S., R.D., nutritionist, division of nutritional sciences, Cornell University, Ithaca, NY. "There are other products which contain trans fatty acids, and there are now margarines which do not contain any trans fat. Shortenings, cookies, crackers and other baked goods are also sources of trans fatty acids, but the trend is not as strong for trans fat-free versions of these products."The heart of the matter  Many health experts feel trans fat studies to date have been inconclusive. But several are raising some prominent red flags. Trans fatty acid intake is related to increased coronary heart disease, according to studies by Dr. Walter Willet, Harvard School of Public Health, Boston, MA. Willet used the effects of trans fatty acids on plasma LDL and HDL levels, and the relation these lipids had on the risk of coronary heart disease, and estimated that trans fatty acids are responsible for 30,000 coronary heart disease-related deaths.  The latest report from the ongoing Nurses' Health Study provides evidence it is the kinds of fats consumed, not the total amount of fat, that determine women's risk of suffering a heart attack. The 14-year study of more than 80,000 nurses found that women who ate the most trans fats had a 53% greater risk of suffering a heart attack than those who consumed the least. Women with the largest consumption of total fat (46% of calories) had no greater risk of having a heart attack than those who ate the least amount of fat (29% of calories).Cancer connection  Some studies claim that trans fatty acids have an effect on tumor development. In addition, evidence suggests that diet is related to the risk of cancer, particularly that of the colon, rectum and breast. These studies indicate that ingesting saturated fat or animal fat increases the risk, while consuming fiber and vegetable products decreases the risk.  "A statistical correlation between trans fatty acid consumption and the risk of breast cancer has been reported," Allred says, "but this does not mean that there is a cause-and-effect relationship. More biological studies need to be conducted to determine whether trans fatty acids have an effect on the initiation or growth of cancer cells."  Because of these studies, FDA is weighing labeling options for trans fatty acid content in foods. The international community isn't as ambivalent about trans fatty acids as is the United States. Danish and Dutch margarine manufacturers must state trans fatty acid content on product labels, and reduce that content to less than 5%.  Again, weighing fat options makes good health sense.  "Current dietary advice to lower risk for coronary heart disease includes lowering your intake of saturated fat, trans fat, total fat, cholesterol and maintaining a healthy body weight," advises Wahida Karmally, M.S., R.D., director, nutrition research unit, The Irving Center for Clinical Research, Columbia Presbyterian Medical Center, New York. "You can limit your intake of trans fatty acids and saturated fatty acids by decreasing your intake of total fat."  Andrea Platzman is a registered dietitian who is a consultant to the food industry, and regularly writes for nutrition publications. She earned a master's degree in nutrition from New York University, and has a culinary and business background.Back to top