Long-chain conversion of 13Clinoleic acid and α-linolenic acid in response to marked changes in their dietary intake in men

We studied the long-chain conversion of U-13Calpha-linolenic acid (ALA) and linoleic acid (LA) and responses of erythrocyte phospholipid composition to variation in the dietary ratios of 18:3n-3 (ALA) and 18:2n-6 (LA) for 12 weeks in 38 moderately hyperlipidemic men. Diets were enriched with either flaxseed oil (FXO; 17 g/day ALA, n=21) or sunflower oil (SO; 17 g/day LA, n=17). The FXO diet induced increases in phospholipid ALA (>3-fold), 20:5n-3 eicosapentaenoic acid (EPA), >2-fold, and 22:5n-3 docosapentaenoic acid (DPA), 50% but no change in 22:6n-3 docosahexanoic acid (DHA), LA, or 20:4n-6 arachidonic acid (AA). The increases in EPA and DPA but not DHA were similar to those in subjects given the SO diet enriched with 3 g of EPA plus DHA from fish oil (n=19). The SO diet induced a small increase in LA but no change in AA. Long-chain conversion of U-13CALA and U-13CLA, calculated from peak plasma 13C concentrations after simple modeling for tracer dilution in subsets from the FXO (n=6) and SO (n=5) diets, was similar but low for the two tracers (i.e., AA, 0.2%; EPA, 0.3%; and DPA, 0.02%) and varied directly with precursor concentrations and inversely with concentrations of fatty acids of the alternative series. 13CDHA formation was very low (<0.01%) with no dietary influences.