N-3 FATTY-ACIDS AND SERUM-LIPOPROTEINS - HUMAN STUDIES

The effects of n-3 fatty acids from fish oils (eicosapentaenoic acid a nd docosahexaenoic acid) and plant oils (alpha-linolenic acid) on huma n serum lipids and lipoproteins are reviewed. Studies were included in this review if they were placebo-controlled, crossover, or parallel d esign studies providing < 7 g n-3 fatty acids/d and with treatment per iods of greater than or equal to 2 wk duration. Only three studies wer e available for evaluation of the effects of alpha-linolenic acid on s erum lipid concentrations. From these studies it appeared that alpha-l inolenic acid (18:3n-3) was equivalent to n-6-rich oils vis-a-vis lipi d and lipoprotein effects. Only when very large amounts of flaxseed oi l were fed did the hallmark effect of marine n-3 fatty acids-reduced t riacylglycerol concentrations-appear. Thus, in terms of effects on lip oprotein metabolism, the plant-derived n-3 fatty acid is not equivalen t to the marine-based acids. More studies using the marine-based acids were examined and summarized. Both crossover (n = 36) and parallel (n = 29) design studies reached the same conclusions: total cholesterol is not materially affected by n-3 fatty acid consumption, low-density- lipoprotein cholesterol concentrations tend to rise by 5-10% and high- density-lipoprotein cholesterol by 1-3%, and serum triacylglycerol con centrations decrease by 25-30%. These effects of marine n-3 fatty acid s are now well-established; what remains is to determine the mechanism s behind these effects and, more importantly, their health consequence s.