rs174553 — FADS1

Intronic variant in the FADS1 gene cluster that reduces delta-5 desaturase activity, impairing conversion of DGLA to arachidonic acid (omega-6) and dietary omega-3 precursors toward EPA, leaving G allele carriers with lower circulating long-chain PUFAs and greater dependence on preformed EPA and DHA

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FADS1 rs174553 — When Your Fatty Acid Factory Runs Slow

Your body cannot synthesize omega-3 and omega-6 fats from scratch. It starts with short-chain precursors — alpha-linolenic acid (ALA) from flaxseed and walnuts for omega-3, linoleic acid (LA) from vegetable oils for omega-6 — and extends them through a series of enzymatic steps into the longer-chain forms that actually drive biology: EPA, DHA, and arachidonic acid (AA). The rate-limiting enzyme in this pipeline is FADS111 FADS1
Fatty acid desaturase 1, also called delta-5 desaturase (D5D); catalyzes the final desaturation step converting DGLA → AA in the omega-6 pathway and ETA → EPA in the omega-3 pathway. rs174553 is an intronic variant in the FADS1 gene cluster that alters how efficiently this enzyme operates — and the difference shows up directly in your blood.

The Mechanism

As an intronic variant22 intronic variant
a DNA change within a non-coding intron; can affect gene expression through regulatory elements, splicing signals, or mRNA stability without altering the protein sequence directly, rs174553 does not change the FADS1 protein. Instead, the G allele sits in a regulatory region of the FADS1 locus that is part of a tight haplotype block across the FADS1-FADS2 cluster on chromosome 11. Multiple studies confirm that carrying the G allele — or the broader minor-allele haplotype it tags — is associated with lower FADS1 desaturase activity across both the omega-6 and omega-3 pathways.

Practically, this means: - DGLA → arachidonic acid (AA): reduced efficiency, lower circulating AA - ETA → EPA: reduced efficiency, lower endogenous EPA from dietary ALA precursors - Precursor accumulation: higher dihomo-gamma-linolenic acid (DGLA) and linoleic acid (LA), which build up when the desaturation step is slow

The A allele, which corresponds to the GRCh38 plus-strand reference at this position, is associated with normal or higher FADS1 activity.

The Evidence

The most rigorous evidence comes from a study of 224 individuals in a geographically isolated founder population33 study of 224 individuals in a geographically isolated founder population
Mathias et al. FADS genetic variants and omega-6 polyunsaturated fatty acid metabolism in a homogeneous island population. J Lipid Res, 2010. Across 16 FADS cluster SNPs tested against 22 fatty acids, rs174553 G allele carriers showed consistently lower omega-6 long-chain PUFAs. The FADS1 omega-6 activity ratio (AA/DGLA) showed the strongest association of any fatty acid measure (p = 2.11×10⁻¹³ to 1.8×10⁻²⁰) — an exceptionally strong signal for a common intronic variant.

In pregnant and lactating women, Xie and Innis demonstrated44 Xie and Innis demonstrated
Xie L, Innis SM. Genetic variants of the FADS1 FADS2 gene cluster are associated with altered (n-6) and (n-3) essential fatty acids in plasma and erythrocyte phospholipids in women during pregnancy and in breast milk during lactation. J Nutr, 2008 that GG homozygotes had lower arachidonic acid, lower EPA, and higher linoleic acid in both plasma phospholipids and red blood cell membranes — confirming the conversion impairment extends into tissue-level fatty acid composition, not just circulating levels.

A key clinical implication emerged from an infant RCT with 276 participants55 infant RCT with 276 participants
Meldrum et al. Can polymorphisms in the FADS gene cluster alter the effects of fish oil supplementation on plasma and erythrocyte fatty acid profiles? Eur J Nutr, 2018 where minor G allele homozygotes across FADS1 SNPs, including rs174553, showed significantly higher DHA levels after fish oil supplementation than other genotypes. This counterintuitive finding — poor converters respond better to preformed DHA — reflects that when endogenous conversion is impaired, exogenous EPA and DHA are incorporated more efficiently because there is less competition from endogenously synthesized product.

Population frequencies vary substantially: the G allele is rare in African populations (~8%) but common in East Asian (~55%) and Latino (~49%) populations, suggesting population-specific dietary adaptations to traditional marine food sources in some ancestry groups.

Practical Actions

For G allele carriers, the core implication is that relying on plant-based omega-3 sources (ALA from flaxseed, chia, walnuts) is insufficient to maintain adequate EPA and DHA levels, because the conversion machinery is slower. GG homozygotes in particular should obtain preformed EPA and DHA directly from marine or algae-based sources, bypassing the impaired desaturation step. Target 2–4 g combined EPA+DHA daily for GG carriers; 1–2 g for AG heterozygotes. Algae-based DHA/EPA supplements are equally effective and suitable for vegetarians.

On the omega-6 side, lower FADS1 activity means less AA is produced — which reduces the substrate for pro-inflammatory eicosanoids. GG carriers may therefore have a lower baseline inflammatory tone from the omega-6 pathway, but this comes at the cost of the reduced EPA and DHA synthesis described above.

Interactions

rs174553 is in high linkage disequilibrium with rs174537, rs174547, and rs174546 in the same FADS1 haplotype block. These variants co-segregate, and carrying the minor haplotype across multiple positions compounds the reduction in desaturase activity. The nearby FADS2 gene (encoding delta-6 desaturase, which acts upstream of FADS1) also contains functionally relevant variants — combined FADS1+FADS2 impairment more severely restricts the full ALA → EPA → DHA conversion pathway than either gene alone.

The ELOVL2 gene (rs953413, rs2397142) encodes the elongase enzyme that operates between FADS steps; ELOVL2 variants that reduce elongase efficiency interact with FADS1 impairment to further reduce DHA synthesis capacity.

Nutrient Interactions

omega-3 fatty acids (ALA) impaired_conversion
eicosapentaenoic acid (EPA) increased_need
docosahexaenoic acid (DHA) increased_need
arachidonic acid (AA) altered_metabolism

Genotype Interpretations

What each possible genotype means for this variant.

AA Efficient Converter Normal

Normal FADS1 activity — efficient omega-3 and omega-6 conversion

The AA genotype is associated with normal FADS1 desaturase activity in studies measuring the AA/DGLA ratio and omega-6 PUFA concentrations. The Mathias et al. (2010) study in a founder population confirmed that the A allele (major/reference allele in global populations outside East Asia and Latin America) is associated with higher FADS1 enzymatic efficiency compared to G allele carriers.

Normal conversion efficiency means your AA levels are maintained through endogenous synthesis, and plant-based ALA can be partially converted to EPA (though conversion is still inefficient even with optimal genetics — the ALA→EPA pathway efficiency is only ~5-15% even in efficient converters). Marine or algae-based EPA/DHA supplements remain beneficial at standard dosages, but you are not at elevated risk of functional EPA deficiency from impaired conversion.

AG Reduced Converter Intermediate

One copy of the G allele — moderately reduced FADS1 activity, partial impairment of long-chain PUFA synthesis

The AG heterozygote falls between the efficient AA converter and the substantially impaired GG homozygote. In the Mathias et al. (2010) founder population study, single G allele carriers showed intermediate FADS1 omega-6 activity ratios compared to the two homozygous groups. The Xie and Innis (2008) study in pregnant women confirmed that plasma and erythrocyte fatty acid profiles reflect genotype in a dose-response fashion, with one G allele producing intermediate reductions in AA and EPA relative to two G alleles.

Because FADS1 is the rate-limiting step for both omega-6 and omega-3 long-chain PUFA synthesis, even partial impairment means your body produces less AA and less endogenous EPA than AA homozygotes. The practical gap is manageable with dietary adjustment toward preformed EPA and DHA.

GG Poor Converter Poor Converter

Two copies of the G allele — substantially reduced FADS1 activity, significant impairment of omega-3 and omega-6 long-chain PUFA synthesis

The GG genotype represents the poorest-converting end of the FADS1 spectrum at this locus. The Mathias et al. (2010) study documented the strongest FADS1 omega-6 activity ratio associations in the entire FADS cluster at rs174553 (p = 2.11×10⁻¹³ to 1.8×10⁻²⁰), with GG carriers showing consistently lower omega-6 long-chain PUFAs compared to AA carriers. In pregnant and lactating women (Xie and Innis, 2008), GG homozygotes showed lower arachidonic acid, lower EPA, and higher linoleic acid in both plasma phospholipids and erythrocyte membranes — confirming that tissue-level fatty acid composition is genuinely altered, not just circulating levels.

The clinical picture is nuanced: lower AA means less substrate for pro-inflammatory omega-6 eicosanoids, which may partly explain why East Asian and some Latino populations (where the G allele is common) have historically had lower incidence of certain inflammatory conditions when consuming traditional marine-heavy diets. However, the same impairment reduces EPA synthesis capacity, creating functional omega-3 deficiency unless preformed EPA and DHA are supplied directly.

The Meldrum et al. (2018) infant RCT found that minor G allele homozygotes had significantly higher DHA levels after fish oil supplementation than other genotypes — GG carriers absorb and incorporate supplemental EPA and DHA more efficiently, likely because there is less competition from endogenous product. This makes supplementation particularly effective in GG individuals.