The effect of dietary energy percentage of fat and its P/S ratio on incorporation of n-3 PUFA and leukotriene production during fish oil supplementation in healthy volunteers.

The effect of low (25 per cent of energy) and high (35 per cent of energy) fat diets with either low (less than 0.4) or high (greater than 1.0) polyunsaturated/saturated fatty acid (P/S) ratios on fatty acid compositions of plasma cholesterol esters and neutrophil phospholipids, and leukotriene production was studied in four groups of healthy volunteers supplemented with 6 g fish oil daily for four weeks. Except for three subjects, eicosapentaenoic acid (20:5n-3) content markedly increased from baseline in the plasma cholesterol ester fraction and to a lesser extent in the neutrophil phospholipid fraction. The increase in the plasma cholesterol ester fraction was inversely, though weakly related to the dietary intake of linoleic acid (18:2n-6). At supplementation endpoints, the 20:5n-3/20:4n-6 ratio in both plasma cholesterol esters and neutrophil phospholipids was highest in the groups consuming diets with low P/S ratio. In vitro leukotriene B5 production by neutrophils, did not differ between groups and there was no consistent suppression of LTB4 production in this four-week study. It is suggested that factors other than the actual dietary 18:2n-6 intake additionally influence the accumulation of 20:5n-3 in tissue during dietary fish oil supplementation.