Linoleate inhibits EPA incorporation from dietary fish-oil supplements in human subjects

Thirty healthy male subjects were randomly allocated into one of two treatment groups: group H subjects were maintained on a hign-linoleic acid (LA) diet with the saturated fatty acids kept low and those in group L were kept on a low-LA, low saturate diet. After a 3-wk run-in period, subjects consumed a fish-oil supplement containing 1.6 g eicosapentaenoic acid (EPA)/d and 0.32 g docosahexaenoic acid as triglycerides for a further 4 wk. The diets alone resulted in a significant change in neutrophil phospholipid LA (H = 12.7 ± 2.9%, L = 9.0 ± 0.9%; P < 0.05). Dietary supplementation with fish oil resulted in a significant increase in EPA in neutrophil phospholipids that was greater in group L (mean 2.0 ± 0.4%) than group H (mean 1.5 ± 0.3%; P < 0.005). Reductions in arachidonic acid concentrations in neutrophil membranes were not different, nor could differences in leukotriene B₄ production be detected. Our study indicates that the ingestion of n-6 fatty acids within the diet is an important determinant of EPA incorporation into neutrophil membranes.