DIETARY TRANS-MONOUNSATURATED FATTY-ACIDS NEGATIVELY IMPACT PLASMA-LIPIDS IN HUMANS - CRITICAL-REVIEW OF THE EVIDENCE

Trans fatty acids (t-FA) are geometrical isomers of unsaturated fatty acids that assume a saturated fatty acid-like configuration. Human die ts contain t-FA derived from animal sources (e.g., dairy products and ruminant meats), but most are supplied by products containing industri ally hydrogenated vegetable oils ( e.g., margarines, shortenings and b aked goods). Typical intake of t-FA in American diets has been estimat ed to be between 8-15 g/day, although wide variation exists between in dividuals. Human clinical studies since 1990 have revealed that relati ve to cis-monounsaturated fatty acids (i.e., oleic acid), t-FA increas e total cholesterol (TC) and low density lipoprotein cholesterol (LDL- C), and tend to decrease high density lipoprotein cholesterol (HDL-C) concentrations. Additionally, t-FA tend to increase the atherogenic li poprotein (a). Thus, t-FA induce an adverse plasma lipid profile (incr eased ratios of TC/LDL-C and LDL-C/HDL-C), which represents increased risk for coronary heart disease. The effects of t-FA on LDL-C and HDL- C appear to be directly related to intake and clinically measurable ab ove 3%en as t-FA. The cholesterol-raising ability of t-FA is analogous to that of the 12-16 carbon saturated fatty acids, possibly reflectin g increased LDL production or delayed LDL clearance. By contrast, t-FA are unlike the saturated fatty acids in their depression of HDL-C. Pr eliminary evidence suggests that at least part of their impact on lipo proteins reflects increased serum cholesteryl ester transfer protein a ctivity, i.e., increased transfer of cholesteryl esters from HDL to LD L. Since the adverse effects of t-FA on human plasma lipids may be con fined to specific isomers, future studies delineating their effects ar e warranted.