Trans fatty acids, lipoproteins, and coronary risk.

Most dietary fatty acids contain at least one double bond, which is usually in the cis configuration. However, biohydrogenation in the rumen of cows and sheep, or catalytic hydrogenation of vegetable oils in the food industries, will convert some of the cis double bonds to the trans configuration. Trans fatty acid intake in western Europe and North America probably ranges from 5 to 15 g/day. Major dietary sources are frying fats used in industrial food preparation, margarines, and other spreads. In the past, margarines contained up to 50% trans fatty acids; however, these are now being phased out. Trans fatty acids raise serum low density lipoprotein (LDL) cholesterol and lower high density lipoprotein (HDL) cholesterol in humans when substituted for cis unsaturated fatty acids in the diet. These effects may be mediated by the cholesteryl ester transfer protein. Trans fatty acids also increase lipoprotein (a) levels relative to other fatty acids. The effects of trans fatty acids on the risk profile for coronary heart disease are thus unfavorable, and labels of food products should state the trans fatty acid content.