1. Eight healthy male volunteers (aged 22–39 years) supplemented their normal daily diet with 15 g encapsulated fish oil (MaxEPA) for a 6 week period. Fasting blood samples were taken before, at the completion of and 3 months after the period of supplementation.
2. Evaluation of nutrient intakes showed that the intake of n-3 polyunsaturated fatty acids rose significantly (P < 0·01) during supplementation. This was reflected in changes in the fatty acid composition of platelet phosphatidyl choline (PC) and phosphatidyl ethanolamine (PE) without any changes in phosphatidyl serine, phosphatidyl inositol or sphingomyelin.
3. In both PC and PE there were significant (P < 0·05) increases in the levels of 18:1 n-9 and 20:5n-3 fatty acids and a significant (P < 0·05) decrease in 20:4n-6 during supplementation. 16:0 rose significantly in PC (P < 0·05) while in PE, 18:0 fell and both 22:5n-3 and 22:6n-3 rose significantly (P < 0·05).
4. There were no significant effects of fish-oil supplementation on serum lipids, platelet cholesterol: phospholipid, collagen-induced platelet aggregation or collagen-induced platelet thromboxane B2 production. However, there was a significant correlation (P < 0·001; r+0·63) between total phospholipid arachidonic acid and platelet thromboxane production.
5. The fluorescent probe 1,6-diphenyl-1,3,5-hexatriene was used to determine whether fish-oil supplementation altered fluorescence polarization of isolated platelet plasma membrane and, by inference, platelet plasma membrane fluidity. No significant effect of fish-oil supplementation on fluorescence polarization was seen.