Effects of fish oil alone and combined with long chain (n-6) fatty acids on some coronary risk factors in male subjects

The effects of fish oil alone were compared with those of fish oil combined 1:1 with evening primrose oil rich in long chain (n-6) fatty acids in a double-blind cross-over study. After administration of fish oil there was a highly significant increase in 20:5 (n-3) (eicosapentaenoic acid) and 22:6 (n-3) (docosahexaenoic acid) and a significant decrease in (n-6) fatty acids in plasma phospholipids. After consumption of the fish oil/evening primrose oil mixture, the increase in (n-3) and the decrease in (n-6) fatty acids were considerably smaller. Triglycerides in serum decreased by 36% (P < 0.01) after the fish oil and by 29% (P < 0.05) after the fish oil/evening primrose oil mixture. Atherogenic index decreased by 12% (P < 0.05) after fish oil/evening primrose oil and by 6% (P = ns) after fish oil alone. This difference was statistically significant (P < 0.05). Plasma homocysteine was reduced by 10% (P < 0.05) after the fish oil/evening primrose oil mixture and decreased 4% (P = ns) after the fish oil alone. Plasma fibrinogen decreased after both oils. The combined oils did not raise plasminogen activator inhibitor-1 (PAI-1) antigen at all, whereas after fish oil there was a 49% (P < 0.05) increase. Fish oil increased the ratio C20:4 to C20:3, an index of delta-5-desaturase, by 96% (P < 0.001) and reduced the ratio of C20:3 to C18:2, an index of delta-6-desaturase, by 38% (P < 0.001), whereas the fish oil/evening primrose oil mixture left these indexes unchanged. A high index of delta-5-desaturase has been found to be correlated to increased insulin sensitivity. In conclusion, combination of fish oil and evening primrose oil had a more favorable effect on the atherogenic index and caused no increase in PAI-1 antigen. The effects on triglycerides and PAI-1 of the fish oil and the mixture appears to be a result of their (n-3) fatty acid content.