Metabolic and atherogenic effects of trans fatty acids

In nearly all naturally occurring unsaturated fats, double bonds are in the cis configuration and these occur most commonly in fixed positions in the aliphatic chain. This parsimony is dictated by the specificity of the enzymes involved in fatty acids synthesis. Because the number and position of double bonds influence the function and metabolism of fatty acids, including their incorporation into phospholipids and their transformation into prostaglandins and other eicosanoids. changes in the fatty acid composition of diets may have profound effects on several physiological processes. For most of human history, oleic, linoleic, linolenic acid, and the longchain n-3 fatty acids from fish oils constituted almost all of the unsaturated fat in the food supply. The only significant source of trans isomers were dairy fat and the meat of ruminants, whose stomach contains bacterial isomerases which can convert the double bonds of dietary fat to a trans configuration. A dramatic change in the fatty acid composition of the food supply occurred at the turn of the century, when a process was discovered to convert liquid oils into solid or semisolid fats [ l ] . During this process, known as partial hydrogenation, oils are heated in the presence of nickel or other metal catalysts and exposed to hydrogen gas. This causes some double bonds to become saturated, whilst others are changed to a trans configuration (geometric isomerism) and/ or shifted to a new position in the aliphatic chain (positional isomerism). Typically, the end-products of partial hydrogenation contain over 20 different isomers of oleic and linoleic acids, which may contribute up to 40% or more of the total fat [2]. Changes in the conditions of partial hydrogenation allow the production of different fats which are employed in the manufacturing of margarine and frying or baking fats. The production of partially hydrogenated vegetable oils rose steadily during the course of the century