The FADS Gene and Omega-3: Why Some People Get Less EPA/DHA from Plants

Key points in 1 minute

• The FADS1 and FADS2 genes build the enzymes that act as a "bottleneck" in converting plant omega-3 (ALA) into the EPA and DHA your body actually uses.
• On average people convert only about 5–10% of ALA into EPA, and less than 1% into DHA — and low-efficiency genetic variants push those numbers even lower.
• Variants (SNPs) in the FADS region, such as rs174537, are clearly associated with differences in blood EPA/DHA levels.
• People with "slow-converter" variants who rely mainly on plant omega-3 (flaxseed, chia, walnuts) may not get enough EPA/DHA, and should consider direct sources from oily fish or algae oil.
• This is a modifiable tendency, not a verdict — genetic data is one tool for planning nutrition, not a diagnosis.

Hello, from the medical team at Geneus DNA. One question I hear constantly is: "I eat flaxseed and chia every day, so why isn't my blood omega-3 going up?" Part of the answer is hidden in a group of genes called FADS. Today I'll walk you through how these genes work, why two people eating the same diet can end up with different EPA/DHA levels, and how this insight can help you choose omega-3 sources more wisely.

Not all omega-3s are the same, and your body uses them differently

When we say "omega-3," we're actually talking about several different fatty acids. The three main ones to know are:

• ALA (alpha-linolenic acid) — the short-chain, plant-based omega-3 found in flaxseed, chia, walnuts, and canola oil. Your body cannot make it, so it is an essential fatty acid.
• EPA (eicosapentaenoic acid) — a long-chain omega-3 involved in regulating inflammation and heart health.
• DHA (docosahexaenoic acid) — a long-chain omega-3 that is a key structural building block of the brain and retina.

The point is that most of the health benefits we hear about, especially for the heart and brain, come mainly from EPA and DHA. Plant-based ALA has to be "converted" into EPA/DHA before it can deliver those benefits — and that is exactly where the FADS genes come in.

The FADS genes: the bottleneck of omega-3 conversion

The FADS1 and FADS2 genes sit next to each other on chromosome 11 and produce two enzymes: delta-5 desaturase (from FADS1) and delta-6 desaturase (from FADS2). Together this pair works like machines on a production line, gradually extending and adding bonds to ALA until it becomes EPA, then continuing on toward DHA.

The problem is that this step is naturally inefficient. Human studies estimate that, on average, we convert only about 5–10% of ALA into EPA and less than 1% into DHA, with women of reproductive age converting slightly better than men due to the influence of estrogen. When conversion is already low, genetic differences matter even more, because they can push these numbers lower still.

How FADS SNPs affect blood omega-3 levels

Single-nucleotide variations, or SNPs, in the FADS region (commonly studied ones include rs174537, rs174546, and rs174575) are associated with how active the desaturase enzymes are. In simple terms:

• People with a high-efficiency haplotype convert ALA into EPA/DHA better and often show higher blood EPA/DHA on the same diet.
• People with a low-efficiency haplotype convert more slowly, so relying on plant ALA alone is harder for them.

Interestingly, the frequency of these variants differs by ancestry, reflecting adaptation to ancestral diets. This is a great example of nutrigenomics, the study of how genes and diet interact.

Who may benefit more from direct EPA/DHA

Based on the mechanism above, the following groups have good reason to consider ready-made EPA/DHA sources rather than relying on plant ALA alone:

• People with low-efficiency FADS variants — especially when confirmed by genetic testing.
• Vegetarians and vegans who don't eat fish and get their omega-3 mainly from ALA — for this group, algae oil is an excellent plant-based EPA/DHA option.
• People whose Omega-3 Index (the proportion of EPA+DHA in red blood cell membranes) tests low despite eating plant sources regularly.

Common direct EPA/DHA sources include oily fish (salmon, mackerel, sardines), fish oil, and algae oil for those who don't eat fish. The advantage of these sources is that they "skip the bottleneck" of the desaturase enzymes entirely, so your body doesn't have to rely as heavily on FADS gene efficiency.

What the science does NOT say — read your results wisely

I want to be clear that our knowledge of the FADS genes has limits worth keeping in mind when interpreting results.

• Association is not always causation — FADS SNPs are "associated" with blood omega-3 levels, but those levels also depend on diet, absorption, and many other factors. Having a slow-converter variant doesn't automatically mean you're omega-3 deficient.
• There is no fixed threshold for exactly how much EPA/DHA a given genotype "needs" — recommendations are tailored to your blood results and individual context.
• The benefit of fish oil supplements on long-term health outcomes (such as heart disease) remains debated in large trials, depending on the dose used and the population studied.

In short, FADS gene data is "one piece of a larger picture" that helps you choose omega-3 sources that suit you better — not a health verdict. Before starting supplements or making major dietary changes, especially if you have a chronic condition or take blood-thinning medication, always consult your doctor first. This same idea of using genetics to guide nutrition also applies to other nutrients, such as vitamin D and genetics.

References

1. National Library of Medicine. FADS1 gene / FADS2 gene, MedlinePlus Genetics. medlineplus.gov
2. Brenna JT, et al. alpha-Linolenic acid supplementation and conversion to n-3 long-chain polyunsaturated fatty acids in humans. Prostaglandins Leukot Essent Fatty Acids. 2009. pubmed.ncbi.nlm.nih.gov
3. Schaeffer L, et al. Common genetic variants of the FADS1 FADS2 gene cluster and their reconstructed haplotypes are associated with fatty acid composition. Human Molecular Genetics. 2006. pubmed.ncbi.nlm.nih.gov
4. National Institutes of Health, Office of Dietary Supplements. Omega-3 Fatty Acids — Health Professional Fact Sheet. ods.od.nih.gov