trans fatty acids and coronary heart disease
trans unsaturated fatty acids are produced commercially in large quantities by heating vegetable oils in the presence of metal catalysts and hydrogen to form shortening and margarine. trans fatty acids are so named because the carbon atoms adjacent to their double bonds are on opposite sides, resulting in a straight configuration and a solid state at room temperature. in contrast, naturally occurring unsaturated fatty acids contain double bonds as cis isomers, with adjacent carbons on the same side of the double bond, resulting in a bent shape and a liquid state at room temperature.
partial hydrogenation, the process used to create trans fatty acids, is primarily used to produce solid fats. however, it also removes essential polyunsaturated fatty acids, such as linolenic acid (omega 3) and linoleic acid (omega 6), because they tend to oxidize, causing the fat to become rancid with prolonged storage or when exposed to the high temperatures used for commercial deep-fat frying. trans fatty acids are also produced in the rumen of cattle, resulting in low levels of these isomers in dairy and beef fat.
production of partially hydrogenated fats began early in the 20th century and increased steadily until about the 1960s, as processed vegetable fats displaced animal fats in the diets of most people in industrialized countries. the initial motivation was lower cost, but health benefits were later purported. levels of trans fatty acids in margarines have declined as softer margarines have become popular. the average per capita consumption of trans fatty acids from partially hydrogenated oils has remained at about 2 percent of calories since the 1960s, because of the increased use of these fats in commercially baked products and fast foods.
by the early 1990s it became apparent that the consumption of trans fatty acids (hydrogenated and partially hydrogenated oils) had uniquely adverse effects on blood lipid levels in metabolic studies and was associated with an increased risk of coronary heart disease in epidemiologic investigations. a 1995 industry-sponsored review concluded that there was insufficient evidence to take action and that further research was needed. since then many more metabolic and epidemiologic studies have confirmed the adverse effects of trans fatty acids, stimulating the food and drug administration to announce plans to include the trans-fatty-acid content of foods on product labels. one important issue is whether to list the amount of trans fatty acids (hydrogenated and partially hydrogenated oils) separately or to combine it with the saturated-fat content.
in this article we shall review the effects of trans fatty acids (hydrogenated and partially hydrogenated oils) on blood lipid levels that have been identified in metabolic studies and the associated risk of coronary heart disease that has been identified in epidemiologic studies.
http://www.recoverymedicine.com/hydrogenated_oils.htm