What this means

FADS1 codes for delta-5 desaturase, a key enzyme in the chain that converts the short plant-derived omega-3 ALA (from flaxseed, walnuts, chia) into the longer-chain EPA and DHA that the body actually uses for membranes and signalling. The rs174537 variant sits in a regulatory region that controls FADS1 expression; the G allele drives more enzyme, so G-carriers convert ALA more efficiently. People on plant-only diets who carry two T alleles can end up with measurably lower EPA/DHA status, and may want to consider algae-derived DHA.

Plants provide a short form of omega-3 (called ALA, from flaxseed, walnuts, chia). Your body has to extend it into the longer forms (EPA and DHA) it actually uses in cell membranes and the brain. The FADS1 enzyme does that conversion. One common version of the gene drives more enzyme; another drives less. If you eat oily fish like salmon regularly, you skip this step and the version of the gene barely matters. But on a plant-only diet with two slow copies, it's worth considering algae-based DHA to top up directly.

Caveats

• On an omnivorous diet eating any oily fish, the FADS1 genotype matters relatively little.
• The variant is well-replicated but effect sizes on circulating EPA/DHA vary by study.
• Allele frequency varies between populations.
• Plant-only eaters can offset slow conversion with algae-based DHA without much trouble.

References

• Schaeffer et al. — Common genetic variants of the FADS1 FADS2 gene cluster and their reconstructed haplotypes are associated with the fatty acid composition in phospholipids (Human Molecular Genetics, 2006)
• Ameur et al. — Genetic adaptation of fatty-acid metabolism: a human-specific haplotype increasing the biosynthesis of long-chain omega-3 and omega-6 fatty acids (AJHG, 2012)