Trans fatty acids are formed during the process of partial hydrogenation in which liquid vegetable oils are converted to margarine and vegetable shortening. Concern has existed that this process may have adverse consequences because natural essential fatty acids are destroyed and the new artifical isomers are structurally similar to saturated fats, lack the essential metabolic activity of the parent compounds, and inhibit the enzymatic destauration of linoleic and linoleic acid. In the past 5 years a series of metabolic studies have provided unequivocal evidence that trans fatty acids increase plasma conentrations of low-density liprotein cholesterol and reduce concentrations of high-density liprotein (HDL) cholesterol relative to the parent natural fat. In these same studies, trans fatty acids increased the plasma metabolic effects and the known relation of blood lipid concentrations to risk of coronary artery disease, we estimate conversevatively that 30,000 premature deaths per year in the United States are attributable to consumption of trans fatty acids with adverse effects of this magnitude or even larger. Because there are no known nutritional benefits of trans fattc acids and clear adverse metabolic consequences exist, prudent public policy would dictate that their consumption be minimized and that information on trans fatty aids content of food be available to consumers.