Two people can eat the exact same handful of walnuts or spoonful of flaxseed oil and end up with meaningfully different amounts of EPA and DHA in their bloodstream afterward. Diet alone does not explain this gap. A significant part of the answer lies in a gene called FADS1, which controls one of the key enzymatic steps your body uses to convert the plant-based omega-3 ALA into the long-chain forms your brain, heart, and cells actually use.
The Conversion Pathway ALA Has to Travel
Alpha-linolenic acid, or ALA, is the omega-3 fatty acid found in plant sources like flaxseed, walnuts, and chia seeds. Unlike EPA and DHA, which the body can use directly, ALA has to be converted through a multi-step biochemical pathway before it becomes useful in the same way. That pathway involves a series of desaturation and elongation reactions, and the enzymes carrying out those reactions are encoded by a small cluster of genes, most notably FADS1, FADS2, and ELOVL2.
FADS1 encodes an enzyme called delta-5 desaturase, which handles one of the later steps in the pathway, converting an intermediate compound into EPA, a step that then feeds into further elongation toward DHA. FADS2, working earlier in the same pathway, encodes delta-6 desaturase, which is generally considered the rate-limiting first step of the whole conversion process. Even in people with fully typical enzyme activity, this conversion pathway is inefficient. Only a modest fraction, commonly estimated in the range of 5 to 10 percent, of dietary ALA is ultimately converted to EPA, and conversion to DHA specifically is lower still.
What Happens When FADS1 Activity Is Reduced
Certain common genetic variants, or single nucleotide polymorphisms (SNPs), in the FADS1 gene are associated with reduced delta-5 desaturase activity. The most studied of these variants, including rs174546 and rs174537, show up in a substantial share of the population, and research using red blood cell fatty acid measurements has found that carriers of the minor alleles tend to have lower levels of long-chain polyunsaturated fatty acids, consistent with less efficient desaturase activity. In practical terms, this means that for someone with these reduced-activity variants, eating ALA-rich plant foods produces a smaller downstream increase in EPA and DHA than it would for someone without them, even when intake is identical.
How Researchers Study This Effect
Much of the research linking FADS1 variants to fatty acid conversion relies on comparing genotype groups after a fish oil or ALA-rich dietary intervention, then measuring the resulting fatty acid composition in blood or red blood cell membranes. A 2025 study looking at FADS1 and a related elongase gene, ELOVL2, found that baseline omega-3 percentages did not differ meaningfully by genotype, but the degree of improvement after fish oil supplementation did vary by genotype, illustrating that these gene variants shape how someone responds to omega-3 intake rather than simply setting a fixed starting point.
An Evolutionary Backstory: Diet Shaped This Gene Over Time
One of the more interesting angles on FADS1 comes from evolutionary genetics rather than clinical nutrition. Research comparing ancient and modern European DNA found that the allele associated with more efficient FADS1 activity became substantially more common after the introduction of farming roughly 8,000 to 10,000 years ago, when European diets shifted from a hunter-gatherer pattern rich in animal foods and seafood toward a more plant-heavy, agricultural diet. The interpretation offered by researchers is that farmers carrying the more efficient variant, sometimes informally referred to as a “vegetarian-favoring” allele, had a metabolic advantage synthesizing long-chain fatty acids from the plant foods that made up more of their diet, and that advantage was favored by natural selection over subsequent generations.
Separately, research looking at populations of different ancestries has found that FADS1 variant frequencies differ considerably by population, with the more efficient “derived” haplotype notably more common in some African populations than in European populations, reflecting different evolutionary dietary pressures across human history. This is a useful reminder that there is no single “normal” human FADS1 profile, genetic variation at this locus has tracked real dietary differences across populations over thousands of years.
What This Means for Vegans, Vegetarians, and Anyone Relying on Plant-Based ALA
For someone eating a diet that includes fish or algae-based DHA directly, FADS1 genotype matters less, since EPA and DHA are already present in a usable form and do not need to be synthesized from ALA at all. The gene becomes far more relevant for people relying on plant sources like flaxseed, chia, or walnuts as their only omega-3 intake, since the entire benefit of that intake depends on a conversion pathway that a substantial share of the population is genetically less equipped to carry out efficiently.
This is one of the more concrete biological reasons that vegans and vegetarians are often advised to seek out a direct source of EPA and DHA, such as an algae-based supplement, rather than relying solely on ALA-rich plant foods and assuming the body will convert enough of it. Since most people do not know their own FADS1 genotype without specific genetic testing, and conversion efficiency cannot be reliably predicted from diet or symptoms alone, a direct algae-based DHA source removes the guesswork and the genetic lottery from the equation entirely.
Frequently Asked Questions
What does the FADS1 gene actually do?
FADS1 encodes an enzyme called delta-5 desaturase, which carries out one of the key steps in converting plant-based ALA into the longer-chain omega-3s EPA and DHA that the body uses directly.
How common are FADS1 variants associated with reduced conversion?
Certain low-activity FADS1 variants, such as rs174546 and rs174537, are common in the general population, and research indicates carriers show measurably lower levels of long-chain omega-3s in blood and red blood cell membranes compared with non-carriers.
Can I find out my own FADS1 genotype?
Genetic testing that includes FADS1 variants exists, though it is not standard practice in most routine medical care and is more commonly used in research settings or specialized nutrigenomic testing services.
Does FADS1 genotype matter if I already take an algae-based DHA supplement?
Less so. FADS1 governs the conversion of ALA into EPA and DHA, but a direct algae-based DHA supplement already provides the long-chain fatty acid itself, bypassing the conversion step and its genetic variability entirely.
Why do FADS1 variant frequencies differ between populations?
Research suggests these differences reflect evolutionary adaptation to different historical diets. Populations with longer histories of plant-heavy agricultural diets show higher frequencies of the more efficient conversion variant, while populations with diets more centered on animal foods and seafood show different variant patterns.
