Dietary oils and FADS1-FADS2 genetic variants modulate [ ¹³C]α-linolenic acid metabolism and plasma fatty acid composition

Background: Desaturation of dietary α-linolenic acid (ALA) to omega-3 (n - 3) long-chain fatty acids (FAs) is mediated through FA desaturases (FADS1-FADS2) and may be influenced by dietary FA composition. Objective: We investigated the effects of diets enriched in flaxseed oil (FXCO) or high-oleic acid canola oil (HOCO) compared with a Western diet (WD) and FADS1-FADS2 single nucleotide polymorphisms (SNPs) on plasma FAs and [U-¹³C]ALA metabolism. Design: In a randomized crossover design, 36 hyperlipidemic subjects consumed 3 isoenergetic diets enriched in FXCO (20.6 g ALA/d), HOCO (2.4 g ALA/d), or WD (1.3 g ALA/d) for 4 wk. On day 27, blood was sampled 0, 24, and 48 h after the subjects (n = 26) consumed 45 mg [U-¹³C]ALA. The subjects were genotyped for 4 FADS SNPs. Results: FXCO increased (P < 0.001) plasma ALA, EPA, and docosapentaenoic acid (DPA), with no change in DHA compared with the HOCO or WD diets. At 24 and 48 h, [U-¹³C]ALA recovered as plasma [¹³C]EPA and [¹³C]DPA were lower (P < 0.001) after the FXCO diet than after the HOCO and WD diets. No change in [ ¹³C]DHA was observed between diets. Minor allele homozygotes of rs174545, rs174583, rs174561, and rs174537 had lower (P < 0.05) plasma EPA, arachidonic acid (AA), EPA/ALA, and AA/linoleic acid compositions and lower (P < 0.05) plasma [¹³C]EPA enrichment at 24 and 48 h in comparison with carriers of the major allele after all diets. SNPs were not associated with plasma composition of DHA or [¹³C]DHA enrichment. Conclusion: An increase in ALA intake resulting in increased plasma EPA composition may be cardioprotective, especially in minor allele homozygotes.