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

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 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 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 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-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 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 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.