FADS1 rs174538: Fatty Acid Metabolism Genetics
The rs174538 single nucleotide polymorphism is an intronic variant located within the fatty acid desaturase gene cluster on chromosome 11. It is primarily associated with variations in fatty acid desaturase enzyme expression and the conversion efficiency of plant-derived polyunsaturated fatty acids into long-chain forms like EPA and DHA. Research shows that carriers of different alleles exhibit measurable differences in circulating lipid and fatty acid profiles.
What each genotype means
Typical fatty acid conversion
Carriers of two C alleles typically have baseline expression of fatty acid desaturase enzymes, which supports the conventional conversion of plant-based alpha-linolenic acid into long-chain omega-3 fatty acids like EPA and DHA. Research shows this genotype is associated with standard endogenous synthesis rates, although overall blood fatty acid levels remain heavily modulated by direct dietary intake. Evidence for specific health outcome changes linked to this variant alone remains limited and variable across different populations.
Carried by approximately 40% to 45% of individuals of European ancestry, but less common in African populations where the T allele is more prevalent.
Intermediate fatty acid conversion
Carrying one copy of the T allele is linked to intermediate fatty acid desaturase activity and slightly altered circulating levels of polyunsaturated fatty acids. Observational studies suggest modest differences in the efficiency of converting dietary precursor fatty acids into EPA and DHA compared to homozygous genotypes. However, because findings vary across ethnic cohorts and tissue compartments, this statistical association does not represent a definitive metabolic impairment.
Carried by approximately 45% to 50% of people of European and East Asian descent.
Altered fatty acid desaturase efficiency
Individuals with two copies of the T allele tend to have altered fatty acid desaturase expression, which research has linked to lower endogenous synthesis of long-chain polyunsaturated fatty acids from dietary plant precursors. While some studies observe lower circulating EPA or altered lipid profiles among TT carriers, the real-world physiological impact is modest and largely dependent on background dietary fatty acid intake. If you have questions about your lipid profile or nutritional needs, discuss them with a qualified healthcare provider or dietitian.
Carried by roughly 10% to 15% of European populations, but observed at much higher frequencies (around 35% to 45%) in individuals of African ancestry.
Genomic Context and the FADS Gene Cluster
The single nucleotide polymorphism rs174538 resides on chromosome 11 within the fatty acid desaturase (FADS) gene cluster. This region contains three tightly linked genes: FADS1, FADS2, and FADS3. These genes share high structural similarity and often demonstrate strong linkage disequilibrium, meaning variations across this region are frequently inherited together in specific haplotypic blocks. The rs174538 variant is an intronic single-base change between cytosine (C) and adenine (T/A depending on strand orientation; commonly annotated as C/T or G/A in genomic references). Although non-coding, rs174538 acts as a key expression quantitative trait locus (eQTL) and proxy marker for regulatory variation that modulates the transcriptional activity of desaturase genes in liver and adipose tissues.
Biological Function of the FADS1 Enzyme
The FADS1 gene encodes delta-5 desaturase, an essential rate-limiting enzyme in the biosynthesis of long-chain polyunsaturated fatty acids (LC-PUFAs). Humans ingest essential precursors, such as alpha-linolenic acid (ALA, an omega-3) and linoleic acid (LA, an omega-6), from plant sources. The delta-5 desaturase enzyme catalyzes the critical desaturation steps required to convert these precursors into biologically active downstream molecules. For omega-3 fatty acids, this pathway facilitates the transformation of ALA into eicosapentaenoic acid (EPA) and subsequently docosahexaenoic acid (DHA). In the omega-6 pathway, it drives the production of arachidonic acid (AA). Variations affecting FADS1 expression directly influence the speed and efficiency with which cells carry out these desaturation steps, shifting relative circulating levels of precursor versus end-product fatty acids.
Scientific Evidence and Metabolic Associations
Multiple genome-wide association studies (GWAS) and biochemical analyses have linked rs174538 and neighboring FADS variants to blood fatty acid concentrations. In general, the major C allele is linked to elevated FADS1 expression, resulting in higher endogenous conversion rates of ALA to EPA and LA to arachidonic acid. Conversely, the alternative allele is associated with attenuated desaturase expression, leading to lower circulating levels of long-chain metabolites like EPA and arachidonic acid, alongside higher levels of their plant-derived precursors. However, current clinical evidence linking rs174538 directly to hard cardiovascular or inflammatory clinical endpoints is considered limited and mixed. While associations with circulating lipid metabolites are robust, downstream disease risks depend heavily on dietary background and environmental interactions.
Ancestral Diversity and Evolutionary History
Allele frequencies for rs174538 and linked FADS variants differ significantly across global populations, reflecting distinct evolutionary selective pressures related to ancestral nutrition. In European populations, the minor allele frequency is approximately 0.35, whereas it reaches higher frequencies in other continental groups, hovering around 0.55 in East Asian populations and roughly 0.65 in African populations. Anthropological genomics suggests that populations whose traditional diets relied heavily on agricultural and plant-based foods experienced positive natural selection for alleles that maximize endogenous conversion of plant fatty acids. In contrast, populations with ancestral diets already rich in marine or animal-derived preformed long-chain fatty acids did not experience the same selective pressure, preserving higher frequencies of lower-efficiency alleles.
Applying Genetic Insights Responsibly
Knowledge of an individual's rs174538 genotype provides educational insight into baseline endogenous fatty acid desaturase activity, but it cannot be used to diagnose any disease or dictate clinical treatments. Carrying a genotype associated with slower conversion efficiency does not indicate a medical deficiency, as humans can directly obtain EPA and DHA through dietary sources such as fatty fish, algae, or fortified foods. Individuals interested in personalizing their dietary intake or taking nutritional supplements should consult a registered dietitian or physician. Any clinical biomarkers, including lipid panels or inflammatory markers, should be interpreted by a healthcare provider alongside holistic lifestyle and clinical factors rather than single-gene genetic tests alone.
How common is this variant?
The rs174538 variant displays significant ancestral diversity, with a minor allele frequency of approximately 0.35 in populations of European ancestry, about 0.55 in East Asian populations, and roughly 0.65 in African populations.
Frequently asked questions
What is the biological function of the FADS1 gene?
The FADS1 gene encodes delta-5 desaturase, an essential enzyme responsible for adding double bonds to polyunsaturated fatty acids. This enzymatic step is critical for converting plant-based fatty acids like ALA and LA into longer, biologically active fats such as EPA, DHA, and arachidonic acid.
Does having the rs174538 variant mean I have an omega-3 deficiency?
No, carrying a variant linked to reduced conversion does not mean you have a clinical deficiency. It simply suggests your body may be less efficient at converting plant-derived ALA into long-chain omega-3s, which can be directly acquired through dietary sources like fish or algae.
Should I change my diet based on my rs174538 genotype?
Genetic test results from single markers should not be used as isolated medical or dietary prescriptions. If you have questions about whether to include more dietary sources of EPA and DHA or use nutritional supplements, discuss your goals with a doctor or registered dietitian.
Why do allele frequencies for rs174538 differ across populations?
Variations across ancestral populations are believed to be the result of natural selection driven by historical diets. Populations that historically depended heavily on agricultural plant-based diets favored alleles with higher conversion efficiency, whereas populations with marine- or animal-rich diets faced different evolutionary pressures.
Sources & further reading
Educational information only, last refreshed 9/12/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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Key regulatory polymorphism governing the efficiency of dietary polyunsaturated fatty acid (PUFA) conversion to arachidonic and eicosapentaenoic acids.
Regulatory variant in FADS1 associated with the efficiency of long-chain polyunsaturated fatty acid biosynthesis.
Variant in the FADS gene cluster associated with plasma levels of long-chain polyunsaturated fatty acids.
The ancestral C allele of this FADS1 variant influences blood fatty acid profiles, specifically reducing arachidonic acid.
Influences the efficiency of processing plant-based Omega-3 into EPA/DHA.
This variant in the FADS1 gene influences how efficiently the body converts plant-based fats into essential Omega-3 and Omega-6 fatty acids.