The association is established; acting on it is not advised
The gene cluster that decides whether your body actually turns flaxseed oil into the omega-3s fish already contain — and no guideline tests it before recommending a source.
Solid lines are connections this site curates. Dashed lines mean the two ends share a research paper — worth knowing, and not a claim that one explains the other.
Plants make one omega-3, alpha-linolenic acid (ALA) — found in flaxseed, chia and walnuts. The two omega-3s with the strongest evidence behind them, EPA and DHA, are what fish accumulate by eating algae that already made them. The human body can convert ALA into EPA and DHA itself, through a chain of desaturase enzymes, but how efficiently varies from person to person — and the biggest known reason is genetic.
FADS1 and FADS2, sitting next to each other on chromosome 11, encode the delta-5 and delta-6 desaturases that run that conversion. A 2006 study of 727 adults found variants across this cluster associated with the fatty acid composition of blood phospholipids at p < 1×10⁻¹³ — not only for arachidonic acid, the omega-6 the same enzymes also process, but for the omega-3s EPA and DPA as well. The effect is large enough that it has since been replicated in dozens of cohorts across different ancestries, with allele frequencies that differ substantially between them.
What this means in practice: someone carrying the low-conversion alleles gets measurably less EPA and DHA from the same ALA intake than someone who does not. For a strict vegetarian or vegan relying on flaxseed or algae-derived ALA, that genotype is a real reason blood levels might lag behind someone eating the same diet. Fish oil and algal-oil supplements sidestep the question entirely, since they already contain EPA and DHA rather than the precursor.
None of this is tested for in practice. No professional body recommends FADS1/FADS2 genotyping before choosing a supplement or a diet, and the workaround — checking an actual omega-3 blood level, or simply taking a preformed EPA/DHA source rather than ALA — is available to everyone regardless of genotype.
Omega-3 fatty acids are fats important for heart and brain health, found directly in fish oil or converted by the body from plant sources like flaxseed oil. A gene cluster affects how well that conversion happens.
If you rely on plant-based ALA, a low-conversion genotype is a real reason blood levels might lag behind someone eating the same diet. Fish oil and algal-oil supplements sidestep the conversion step entirely, since they already contain EPA and DHA.
No professional body recommends FADS1/FADS2 genotyping before choosing a supplement or diet. Checking an actual blood omega-3 level is the practical alternative, available to anyone.
Yes — the same enzymes process both, and the original study found its strongest associations with arachidonic acid, an omega-6, alongside the omega-3s EPA and DPA.
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Omega-3 fatty acids (fish oil). MyGeneLog™. https://www.mygenelog.com/supplements/omega-3
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