FADS1 Genotype

If you have ever wondered why fish oil seems to shift your blood omega-3 levels differently than a friend's on the same dose, part of the answer may be written into your DNA. The FADS1 (fatty acid desaturase 1) gene carries the instructions for an enzyme that converts the shorter fats you eat into the longer omega-3 and omega-6 fats your cells, brain, and heart actually use.

This test reads which version of FADS1 you inherited. The result is a one-time genetic readout that helps explain how efficiently your body builds long-chain fats like arachidonic acid (AA), EPA, and DHA from dietary precursors, and how strongly your body might respond to changes in fish oil, plant oils, or omega-rich foods.

What FADS1 Actually Does

FADS1 codes for a converter enzyme called delta-5 desaturase. Its job is to take the shorter fats you get from food (linoleic acid from seed oils and alpha-linolenic acid from plants like flax) and step them up into the longer fats your body uses for cell membranes, brain tissue, and inflammation signaling. Some people inherit a highly active version of this gene. Others inherit a less active version, which tends to leave them with lower baseline long-chain omega-3 levels and a stronger case for getting EPA and DHA directly from oily fish or supplements rather than relying on plant precursors to be efficiently converted.

Several common single-letter changes in this gene (called SNPs, with names like rs174546, rs174547, rs174550, and rs174556) shift the enzyme's output. Carriers of the less active version tend to have lower blood levels of AA, EPA, and DHA and higher levels of the precursor linoleic acid. Carriers of the more active version convert short fats into long ones more readily.

Why This Genotype Matters

FADS1 sits upstream of nearly every fat-related health pathway. The fats it helps produce go on to build cell membranes, fuel brain development, regulate inflammation, and influence cholesterol particles. Because the gene's effect shows up in blood, liver, fat tissue, and even breast milk, your inherited version quietly shapes a wide range of biology.

In a meta-analysis of the common rs174556 variant, A-allele carriers had significantly lower blood levels of AA, EPA, and DHA and higher linoleic acid in blood samples (the higher linoleic acid pattern was seen in blood but not in the breast milk subgroup). In studies of pregnant and lactating women, minor-allele homozygotes had lower AA, EPA, and DHA in plasma, red blood cells, and breast milk. The pattern repeats across populations: the genotype you carry partly sets your baseline omega-3 and omega-6 status, regardless of how well you eat.

Heart and Metabolic Health

FADS1 variants have been linked to cardiometabolic traits in several human studies. In a small case-control study of 120 newly diagnosed type 2 diabetes patients, the C allele of rs174547 was more common and was tied to lower desaturase activity. This is a single small study, and at the genome-wide level FADS1-2-3 variants have not been robustly tied to overall risk of type 2 diabetes or atherosclerotic cardiovascular disease, even though they do shift lipids, inflammatory markers, and fasting glucose. Other observational work has connected FADS1 variants to differences in cholesterol, triglycerides, and arterial stiffness.

A study of 154 people found that certain FADS1 variants were associated with higher liver fat content and lower hepatic FADS1 expression, suggesting the genotype can quietly influence fat handling in the liver. Population data from a survey of Brazilian adults showed that some FADS1 variants associate with more favorable lipid patterns and may mark lower cardiometabolic risk, while others appear to track in the opposite direction depending on which allele is involved.

How You Respond to Fish Oil and Plant Oils

This is where FADS1 testing becomes most practical. Several randomized and controlled trials show that your genotype changes how much your blood fat profile shifts when you take omega-3 supplements or change cooking oils.

In a randomized trial of adults with obesity, those carrying the rs174547 variant of FADS1 showed meaningful changes in red blood cell fatty acid composition after omega-3 supplementation. Large cohort data from the Nurses' Health Study and Health Professionals Follow-Up Study (n=2,288) show that minor-allele (less active) carriers actually have a larger proportional increase in circulating EPA per unit of dietary EPA/DHA intake than major-allele carriers, even though they start from a lower baseline. In a clinical trial of botanical oils, a modest daily dose raised blood GLA and DGLA in a way that depended on the rs174537 genotype. In a separate genotype-based randomized trial on linoleic and alpha-linolenic acid-rich plant oils, the FADS1 genotype shaped the metabolic response. And in an exploratory study, people with the CC genotype of rs174550 saw bigger improvements in cellular energy production after an alpha-linolenic acid-enriched diet.

In breast milk research from mother-infant pairs, DHA levels rose with fish and fish-oil intake only in mothers carrying the major allele. Mothers with the minor allele needed direct DHA sources to bring milk levels up, because their bodies could not efficiently make DHA from shorter fats.

Pregnancy and Early Life

In pregnant and lactating women, FADS1 and the nearby FADS2 variants shape the AA, EPA, and DHA in maternal blood and breast milk. A study of 1,931 mother-child pairs using FADS variants in a Mendelian randomization design also linked variations in this gene cluster to gestation duration, suggesting that long-chain fat metabolism may influence the timing of birth. The takeaway is that what your genotype means for your body extends to what it can pass on through pregnancy and breastfeeding.

One-Time Result, Lifelong Use

FADS1 genotype is fixed from birth. You do not retest it, and the result does not change year to year. The value comes from what you do with the information over the long run.

If you carry the less active version, you have a stronger case for getting long-chain omega-3s (EPA and DHA) directly from oily fish or supplements rather than relying on plant-based alpha-linolenic acid to be efficiently converted. If you carry the more active version, plant sources may meet a larger share of your needs. Either way, what should be retested over time is the downstream picture: your Omega-3 Index, a fatty acid panel, lipid markers, and inflammation markers like hs-CRP (high-sensitivity C-reactive protein). A reasonable cadence is a baseline now, a follow-up 3 to 6 months after any meaningful change in diet or supplements, and at least annual checks on the downstream fats themselves.

What to Do With an Unexpected Result

FADS1 genotyping is a research-grade marker, not a clinical diagnosis. A risk-associated genotype does not mean you will develop heart disease, diabetes, or fatty liver. It means your body's chemistry for handling certain fats is tilted in a particular direction, and that tilt becomes more clinically relevant when it stacks with other risks.

If your genotype suggests reduced conversion efficiency, the most useful next step is to measure the fats themselves. Pair this test with an Omega-3 Index or fatty acid panel to see whether the genetic prediction is showing up in your blood. Layer on a lipid panel, hs-CRP, and HbA1c (hemoglobin A1c, a three-month measure of average blood sugar) to see the broader cardiometabolic picture. If multiple downstream markers are off, a lipidologist, cardiologist, or genetic counselor can help integrate the findings. The genotype itself does not need to be repeated.

Limits of What This Test Can Tell You

FADS1 is a research-stage genetic marker. There are no standardized clinical cutpoints, and no guideline body currently recommends ordering it as part of routine care. The available evidence shows consistent biological effects on blood fat composition, but does not yet show that genotype-based testing changes hard outcomes like heart attacks or strokes in real-world practice. At the genome-wide level, FADS1 variants have not been robustly linked to overall risk of type 2 diabetes or atherosclerotic cardiovascular disease, even though they clearly shift intermediate cardiometabolic traits.

This test detects only the specific FADS1 variants the assay is designed to read. It does not capture every rare variant in the gene, and it does not test FADS2, ELOVL2, or other genes in the same pathway that also shape fat metabolism. The clinical meaning of any single variant can also differ by ancestry, since allele frequencies vary across populations. And carrying a risk variant does not guarantee you will develop any associated condition. Many factors, including diet, exercise, and other genes, ultimately decide that.