rs174541 — FADS1 FADS1 C>G (delta-5 desaturase depth)

Intronic regulatory variant in FADS1 that reduces delta-5 desaturase expression and activity, impairing conversion of dietary omega-6 and omega-3 precursors to arachidonic acid and EPA respectively; independently associated with plasma triglyceride levels and omega-3/omega-6 fatty acid ratios.

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FADS1 rs174541 — Delta-5 Desaturase Depth

Your body's ability to build long-chain omega-3 and omega-6 fatty acids from dietary precursors hinges on a single enzyme: delta-5 desaturase11 delta-5 desaturase
FADS1 (Fatty Acid Desaturase 1) — the enzyme that adds a double bond at the fifth carbon position, converting DGLA to arachidonic acid in the omega-6 pathway and eicosatetraenoic acid (ETA) to EPA in the omega-3 pathway. rs174541 is an intronic variant in the FADS gene cluster on chromosome 11q12.2 that acts as an independent regulator of how much FADS1 enzyme your cells make. The C allele dampens FADS1 expression, reducing the throughput of both the omega-6 pathway (less arachidonic acid from dietary linoleic acid) and the omega-3 pathway (less EPA from plant-derived ALA). Because the C allele also affects circulating triglyceride concentrations, this variant sits at the junction between fatty acid metabolism and broader cardiometabolic risk.

The Mechanism

rs174541 sits within FADS1's intronic regulatory architecture, in high linkage disequilibrium with the established functional cluster of FADS1 variants (rs174546, rs174547, rs174548, rs174537). Intronic variants in this region influence transcription factor binding sites and enhancer elements between FADS1 and FADS2 — the C allele at rs174541 tracks with reduced FADS1 mRNA levels and lower delta-5 desaturase enzyme activity across liver and blood cells.

The functional consequence plays out across two metabolic pathways simultaneously. In the omega-6 pathway: dietary linoleic acid (LA) → GLA → DGLA → [delta-5 desaturase] → arachidonic acid (AA). Reduced FADS1 activity means more DGLA accumulates and less AA is produced. In the omega-3 pathway: plant ALA → stearidonic acid → ETA → [delta-5 desaturase] → EPA. Again, the rate-limiting step is impaired, meaning less EPA is synthesised from the plant-sourced precursor. Neither pathway can compensate for the other — both require the same enzyme.

The Evidence

A Bayesian quantitative trait nucleotide analysis22 Bayesian quantitative trait nucleotide analysis
Voruganti et al. Variants in CPT1A, FADS1, and FADS2 are Associated with Higher Levels of Estimated Plasma and Erythrocyte Delta-5 Desaturases in Alaskan Eskimos. Front Genet, 2012 in 761 Alaskan Eskimos assigned rs174541 a posterior probability >0.8 for functional effect on erythrocyte delta-5 desaturase activity — the strongest statistical evidence available in a Bayesian framework for a variant being causally linked to its phenotype, not merely in LD with the causal site.

The broader FADS1 locus evidence is overwhelming. A landmark GWAS in the InCHIANTI study33 landmark GWAS in the InCHIANTI study
Tanaka et al. Genome-wide association study of plasma polyunsaturated fatty acids in the InCHIANTI Study. PLoS Genet, 2009 of 1,075 Italian adults found that FADS1 cluster variants explain 18.6% of all additive variance in circulating arachidonic acid (p=5.95×10⁻⁴⁶), by far the largest explained variance for any common PUFA-metabolism variant. The CHARGE Consortium meta-analysis44 CHARGE Consortium meta-analysis
Lemaitre et al. Genetic loci associated with plasma phospholipid n-3 fatty acids. PLoS Genet, 2011 across 8,866 European ancestry participants confirmed that FADS1 minor alleles are the dominant genetic predictor of lower circulating EPA (p=5×10⁻⁵⁸) and higher plant ALA (p=3×10⁻⁶⁴).

Beyond fatty acid ratios, FADS1 variants have direct consequences for clinical lipid panels. In 21,004 Japanese individuals55 21,004 Japanese individuals
Nakayama et al. A single nucleotide polymorphism in the FADS1/FADS2 gene is associated with plasma lipid profiles. Hum Genet, 2010, the C allele at the tightly linked rs174547 was significantly associated with higher triglycerides (p=1.5×10⁻⁶) and lower HDL-C (p=0.03), demonstrating that FADS1 reduced activity has effects visible on a standard fasting lipid panel — not just on specialised PUFA measurements. A study of 8,842 Korean adults66 study of 8,842 Korean adults
Lee et al. Functional Impact of the FADS1 rs174546 Single Nucleotide Polymorphism on Serum Lipid Levels. Mol Nutr Food Res, 2024 quantified this: the FADS1 minor allele increases fasting serum triglycerides by 6.48 ± 1.84 mg/dL per allele, mediated through reduced LC-PUFA production and downstream effects on VLDL assembly and clearance.

Practical Actions

For C allele carriers, the core problem is that dietary plant-based omega-3 sources (flaxseed, chia, walnuts, canola oil) supply ALA which requires FADS1 to reach EPA. When FADS1 activity is reduced, that conversion chain slows — the ALA enters the bloodstream but stalls before reaching EPA. Direct supplementation with preformed EPA and DHA from marine or algae-based sources entirely bypasses the impaired step. The dosage depends on genotype: CT carriers benefit from 1–2 g EPA+DHA daily; CC homozygotes need 2–4 g to overcome the more complete impairment.

The triglyceride finding adds a monitoring dimension. If you carry the C allele and have other cardiovascular risk factors, a fasting lipid panel captures the clinical footprint of this genotype — elevated triglycerides and reduced HDL are the measurable downstream signal of impaired FADS1 activity.

Interactions

rs174541 is in high linkage disequilibrium (r² >0.8) with the established FADS1 functional cluster including rs174547, rs174548, rs174546, and rs174537. Users may carry risk alleles at multiple sites on the same haplotype — carrying the C allele at rs174541 in combination with risk alleles at rs174548 and rs174547 increases the probability of being on the full reduced-function FADS1 haplotype. No additional effect beyond what each individual variant predicts is needed for interpretation, as the variants tag the same underlying expression phenotype.

The ELOVL2 gene variant rs17606561 (also in the platform) encodes elongase 2, which converts EPA to DHA. A user who carries both FADS1 reduced-activity alleles and an ELOVL2 impairment faces a double block in the ALA → EPA → DHA pathway, potentially producing the most severe DHA deficiency of any single-enzyme genotype combination. For such users, a DHA-specific supplement target (≥500 mg DHA per day) matters beyond total EPA+DHA.

Nutrient Interactions

alpha-linolenic acid (ALA) impaired_conversion
linoleic acid (LA) impaired_conversion
eicosapentaenoic acid (EPA) increased_need
DHA (docosahexaenoic acid) increased_need
arachidonic acid (AA) altered_metabolism

Genotype Interpretations

What each possible genotype means for this variant.

TT Efficient Converter Normal

Normal delta-5 desaturase activity — effective omega-3 and omega-6 conversion

The TT genotype is associated with normal FADS1 mRNA levels and full delta-5 desaturase activity. In GWAS studies of the FADS1 cluster, individuals on the T/T haplotype show lower precursor fatty acid concentrations (ALA, LA, DGLA) and higher long-chain product levels (AA, EPA), consistent with an uninhibited desaturation step.

Population stratified data show this is the common allele in African ancestry populations (>96% T frequency), where historically higher consumption of preformed AA from animal-protein diets may have reduced evolutionary pressure to maintain high FADS1 activity. In European populations the T allele frequency is approximately 65%, making TT the second most common genotype after CT heterozygotes.

CT Intermediate Converter Intermediate

One C allele — partially reduced FADS1 activity with modest impact on omega-3 conversion and triglycerides

Heterozygotes show intermediate FADS1 mRNA levels and partial delta-5 desaturase activity. The CHARGE Consortium meta-analysis confirmed that each C allele copy shifts circulating fatty acid profiles toward higher precursor accumulation (ALA, DGLA) and lower long-chain products (EPA, AA), with effects scaling linearly with allele dose.

For CT carriers, the conversion impairment becomes clinically relevant when dietary intake of preformed EPA and DHA is consistently low — such as in vegetarians, vegans, or individuals who rarely eat fatty fish. The triglyceride effect (approximately 3–6 mg/dL per allele based on data from linked variants) is modest at one allele but becomes more meaningful when combined with other cardiometabolic risk factors.

CC Poor Converter Poor Converter

Two C alleles — substantially reduced FADS1 activity with impaired EPA synthesis and elevated triglycerides

The CC genotype carries the full reduced-function FADS1 haplotype. In population studies, two C alleles produce the lowest circulating AA and EPA levels at baseline, the highest precursor accumulation (ALA, DGLA), and the most pronounced triglyceride elevation. In the Nakayama et al. 2010 study of Japanese individuals, each minor allele at the tightly linked rs174547 increased triglycerides at p=1.5×10⁻⁶ — in CC homozygotes, this represents approximately two allele-doses of effect, detectable as elevated fasting triglycerides on a standard lipid panel.

The triglyceride mechanism connects to FADS1's role in producing LC-PUFAs that modulate VLDL particle lipid composition. Reduced AA production alters the phospholipid content of VLDL particles, affecting hepatic lipase clearance and postprandial triglyceride disposal.

The omega-3 impact is most consequential for individuals on plant-based diets. In CC homozygotes, eating flaxseed daily will raise plasma ALA but will not translate into meaningful EPA elevation — the conversion bottleneck at FADS1 is severe enough that this pathway cannot be relied upon. Only preformed EPA from marine sources or algae-based supplements bypasses the block entirely. Intervention studies with related FADS1 cluster variants confirm that poor converters show the greatest proportional EPA response to supplementation, suggesting the baseline deficit creates more room for improvement.