Understanding Trans Fatty Acids Reprinted from Food Insight March/April 1993 Recent questions about the role of trans fatty acids in raising blood cholesterol levels should not cause people to make wholesale changes in their diets, according to Margo A. Denke, M.D., assistant professor in the Department of Medicine at the University of Texas Southwestern Medical Center for Human Nutrition. "The trans fatty acids story is a very minor point in a cholesterol-lowering diet, " Denke said at the AMA/IFIC media briefing in New York. "It shouldn't motivate people to change from margarine back to butter. The most important thing in the diet is still saturated fat, " she said. Hydrogenation Trans fats are a type of fat found naturally in some foods . They also are formed when polyunsaturated or monounsaturated fats undergo hydrogenation, a process whereby hydrogen molecules are added to the oils to improve their stability and utility in certain foods. Because vegetable oils are often hydrogenated to produce shortenings and margarines, reports of trans fatty acids research are often described in terms of the merits of butter versus margarine. Health authorities have long recommended a reduced intake of certain saturated fats such as butter and lard, because of their ability to raise blood cholesterol levels. But a 1990 study by Ronald Mensink, M.D., and Martijn Katan, M.D., of the Netherlands, showed very high intakes of trans fatty acids might behave like some saturates in raising blood cholesterol and low- density lipoprotein (LDL) levels, a class of lipoproteins associated with cholesterol deposits on artery walls. Since the study used about seven times more hydrogenated oil than normally consumed by Americans per day, however, the relevance of the findings have been questioned. Subsequent studies using amounts of trans fatty acids typically consumed by Americans have shown total and LDL cholesterol levels may be raised in a direction similar to saturated fat, but not to the same degree. In addition, trans fatty acids account for only a small component of total fat intake. Of the total fat consumed by typical Americans each day, only about six to eight grams come from trans fatty acids. "Trans fats account for 2 percent to 3 percent of the daily calories compared to 14 percent from saturated fat, " Denke said. "Therefore the focus should be on modifying intake of total fat and saturated fat. People need to realize that it's not just the type of fat used, but how much fat, " she said. Denke urged caution in translating the results of initial studies on trans fatty acids into public policy. "It has taken at least 30 studies to confirm the hypercholesterolemic effects of saturated fats. Much more research on trans fats still needs to be conducted, " she advised. From Past to Present Scientific examination of specific fatty acids is relatively recent. In the late 1950s, researchers were just beginning to investigate the fat/cholesterol hypothesis. By the 1980s, the focus had advanced to components of blood cholesterol such as lipoproteins and triglycerides. Today, researchers are taking a microscopic view of fatty acids to assess whether individual characteristics such as carbon-chain links affect cholesterol and lipoprotein levels. "One interesting example is stearic fatty acid, a saturated fatty acid with an 18-carbon chain, " explained Denke. "While many fats contain very little stearic acid, cocoa butter and beef tallow have high levels of this fatty acid. " Research as far back as the 1940s and 1950s indicates stearic acid does not raise blood cholesterol levels like other saturated fatty acids. Studies suggest this paradoxical action may be due to the fatty acid's metabolism. Shortly after absorption, most of the dietary stearic acid is desaturated to oleic acid, a monounsaturated fatty acid. Dietary Recommendations As scientific knowledge about dietary fat continues to evolve, Denke advises Americans to practice balance, variety and moderation in their daily food choices. "From a scientist's perspective, the goal is to discover the ultimate element, the building block, that might be a causal factor in raising cholesterol levels, " Denke said. "But it still must be put into the context of the overall diet. " She concluded, "The best advice remains to modify total dietary fat to 30 percent of calories over time, reduce saturated fat, and eat plenty of fruits, vegetables and whole grains. " Reprinted from the International Food Information Council Foundation, 1993

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