rs174548 — FADS1

FADS1 rs174548 — The Omega-3 Bottleneck

Your ability to build the long-chain omega-3s that your brain, heart, and immune system rely on is not just about what you eat — it depends on how efficiently your body can convert short-chain fatty acids into their active forms. FADS1 encodes delta-5 desaturase¹¹ delta-5 desaturase
The rate-limiting enzyme that adds a double bond at the delta-5 position of the carbon chain, catalysing the conversion of DGLA (an n-6 fatty acid) to arachidonic acid (AA) and dihomo-gamma-linolenic acid to EPA in the omega-3 pathway, the enzyme that sits at the critical bottleneck where plant-derived short-chain fatty acids are elongated into the biologically potent long-chain PUFAs²² long-chain PUFAs
Long-chain polyunsaturated fatty acids (LC-PUFAs) include arachidonic acid (AA, C20:4n-6), EPA (eicosapentaenoic acid, C20:5n-3), and DHA (docosahexaenoic acid, C22:6n-3) — the forms actually used in cell membranes and signalling that your cells actually use.

rs174548 is an intronic variant in FADS1 that influences how much of this enzyme gets made. It sits in high linkage disequilibrium with a cluster of functionally related FADS1 variants, making it one of the top GWAS signals for plasma PUFA levels across multiple large studies. The G allele reduces FADS1 gene expression, dampening delta-5 desaturase activity and impairing the conversion of dietary omega-6 linoleic acid (LA) to arachidonic acid and dietary omega-3 alpha-linolenic acid (ALA) to EPA.

The Mechanism

In the n-6 pathway: LA → GLA → DGLA → [delta-5 desaturase] → AA. In the n-3 pathway: ALA → SDA → ETE → [delta-5 desaturase] → EPA. When delta-5 desaturase activity is reduced, both pathways back up at the same step. The G allele at rs174548 is associated with lower FADS1 mRNA expression in liver and blood ³³ Wang et al. Metabolome-wide association study identified the association between a circulating polyunsaturated fatty acids variant rs174548 and lung cancer. Carcinogenesis, 2017, translating directly to measurable changes in fatty acid profiles: higher precursor levels (LA, ALA, DGLA) and lower product levels (AA, EPA). This is not a rare mutation — the G allele is carried by roughly 30% of Europeans and nearly 60% of Latino populations, reflecting differential evolutionary selection pressure associated with ancestral dietary patterns.

The Evidence

A genome-wide association study in the InCHIANTI cohort⁴⁴ genome-wide association study in the InCHIANTI cohort
Tanaka T et al. Genome-wide association study of plasma polyunsaturated fatty acids in the InCHIANTI Study. PLoS Genet, 2009 of 1,075 Italian adults identified the FADS1 locus as the single strongest genetic determinant of plasma PUFA levels, with the lead SNP explaining 18.6% of additive variance in arachidonic acid — a remarkably large effect for a common variant. Replication in 1,076 subjects from the GOLDN study confirmed the signal.

A CHARGE consortium meta-analysis⁵⁵ CHARGE consortium meta-analysis
Smith CE et al. Dietary fatty acids modulate associations between genetic variants and circulating fatty acids in plasma and erythrocyte membranes: meta-analysis of nine studies. Mol Nutr Food Res, 2015 of 11,668 participants across nine cohorts specifically examined rs174548 alongside rs174538 in FADS1. The study found compartment-specific gene-diet interactions: dietary alpha-linolenic and linoleic acid intake modified the genetic association with DHA and DPA in plasma versus erythrocyte membranes, underscoring that the G allele's impact depends partly on what you eat.

A metabolome-wide association study⁶⁶ metabolome-wide association study
Wang C et al. Metabolome-wide association study identified the association between a circulating polyunsaturated fatty acids variant rs174548 and lung cancer. Carcinogenesis, 2017 validated the rs174548–PUFA link in 253 Chinese subjects (beta = −0.57, P = 1.68 × 10⁻³⁾ and additionally showed the G allele associated with reduced FADS1 gene expression (beta = −0.84, P = 6.49 × 10^−3). The same study found the G allele was associated with reduced lung cancer risk (OR_meta = 0.87, P = 1.76 × 10⁻¹⁵ across 32,292 Europeans and Asians), suggesting PUFA pathway modulation has broader tissue-level consequences.

Practical Actions

For GG homozygotes — roughly 9% of Europeans — the impairment in PUFA conversion is substantial. Eating flaxseed, chia, or walnuts for their omega-3 content will raise ALA in the blood but will not efficiently translate to EPA or DHA, the forms that reduce cardiovascular risk and support brain function. These individuals benefit most from direct preformed EPA/DHA supplementation from marine sources (fish oil or algae). A supplementation trial⁷⁷ supplementation trial
Meldrum SJ et al. Can polymorphisms in the fatty acid desaturase gene cluster alter the effects of fish oil supplementation on plasma and erythrocyte fatty acid profiles? Eur J Nutr, 2018 found minor homozygous carriers of FADS1 cluster SNPs (including rs174548) showed significantly greater DHA increases with fish oil supplementation than other genotypes — consistent with greater baseline deficit and more room for improvement.

For CG heterozygotes, the conversion impairment is partial but meaningful, especially for vegetarians, vegans, and those who rarely eat fish.

Interactions

rs174548 is in high linkage disequilibrium with rs174547, rs174546, and rs174537 within the FADS1–FADS2–FADS3 gene cluster on chromosome 11q12. These variants often travel together as a haplotype, and GWAS signals for PUFA levels frequently colocalize across this region. rs17606561 in the neighboring ELOVL2 gene (elongase 2, which extends EPA to DHA) interacts with FADS1 variants to further influence DHA synthesis capacity — individuals with impaired function in both enzymes may have particularly pronounced DHA deficiency.

Dietary context matters: the CHARGE consortium analysis showed gene-diet interactions, with the G allele's impact on circulating DHA modified by dietary ALA intake. Even poor converters can partially compensate through very high fish intake or direct supplementation.