n-3 fatty acids and serum lipoproteins: human studies

Abstract

The effects of n-3 fatty acids from fish oils (eicosapentaenoic acid and docosahexaenoic acid) and plant oils (alpha-linolenic acid) on human serum lipids and lipoproteins are reviewed. Studies were included in this review if they were placebo-controlled, crossover, or parallel design studies providing < 7 g n-3 fatty acids/d and with treatment periods of > or = 2 wk duration. Only three studies were available for evaluation of the effects of alpha-linolenic acid on serum lipid concentrations. From these studies it appeared that alpha-linolenic acid (18:3n-3) was equivalent to n-6-rich oils vis-vis lipid and lipoprotein effects. Only when very large amounts of flaxseed oil were fed did the hallmark effect of marine n-3 fatty acids-reduced triacylglycerol concentrations-appear. Thus, in terms of effects on lipoprotein metabolism, the plant-derived n-3 fatty acid is not equivalent 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 concentrations decrease by 25-30%. These effects of marine n-3 fatty acids are now well-established; what remains is to determine the mechanisms behind these effects and, more importantly, their health consequences.

Effects of enhanced consumption of fruit and vegetables on plasma antioxidant status and oxidative resistance of LDL in smokers supplemented with fish oil

“…The 7% increase in plasma LDL concentration and 28% decrease in plasma triglyceride concentration agree well with the 5-10% increase in LDL and 20-30% decrease in triglycerides observed in a recent review of EPA/DHA supplementation studies (Harris, 1997). These observations, together with the observed increases in plasma phospholipid EPA and DHA concentrations, indicate that subjects complied with the fish oil supplementation protocol.…”

Effects of trans- and n-3 unsaturated fatty acids on cardiovascular risk markers in healthy males. An 8 weeks dietary intervention study

“…This further emphasizes the need for investigating other mechanisms of action of these food components on CHD risk. The effects of the n-3 PUFA diet on HDL-C and triglycerides were parallel to results from the majority of other studies (Harris, 1997).…”

Effects of docosahexaenoic acid supplementation on blood lipids, estrogen metabolism, and in vivo oxidative stress in postmenopausal vegetarian women

“…Plasma TG level decreased by 18%, which did not reach statistical significance and was not as pronounced as the findings reported in other studies (25-30%) (Harris, 1997). The mild effect might be due to the low daily dose of n-3 fatty acids and original favorable lipid profiles in these postmenopausal vegetarians.…”