Do FADS1/FADS2 variants alter omega-6 conversion toward arachidonic acid?

Genetic variations within the FADS1 and FADS2 gene cluster dictate how individuals metabolize dietary omega-6 fatty acids, directly influencing the pathway's rate-limiting enzymatic steps.

Molecular and metabolic mechanisms

• Enzymatic cascade: FADS2 encodes delta-6 desaturase, which initiates the pathway by converting linoleic acid (LA) to gamma-linolenic acid (GLA). Sequentially, FADS1 encodes delta-5 desaturase, which catalyzes the final conversion of dihomo-gamma-linolenic acid (DGLA) to arachidonic acid (AA).
• Genotypic variations: Individuals carrying "high-activity" alleles—such as the rs174537 G allele or the rs174546 C allele—exhibit significantly elevated desaturase activity, reflected in high product-to-precursor ratios (AA:LA). Low-activity variants (e.g., rs174550 or rs174547 minor alleles) limit this conversion efficiency.
• Inflammatory pathways: Accelerating the conversion of LA to AA expands the intracellular substrate pool, directly driving the production of pro-inflammatory eicosanoids. This upregulation of eicosanoids is linked to increased arterial inflammation and cardiovascular risk.

Dietary interaction and substrate load

• Substrate saturation: When dietary omega-6 intake is high (e.g., representing approximately 10% of total energy), the enzymatic capacity of FADS1/FADS2 becomes a critical metabolic bottleneck.
• Genotype-dependent divergence: Under a high-LA dietary load, individuals with high-activity genotypes experience accelerated conversion, resulting in high levels of circulating AA and inflammatory mediators. In contrast, low-activity carriers reach enzymatic saturation, causing precursor substrates (LA and DGLA) to accumulate while downstream AA levels plateau or decrease.

Bottom line

• FADS1/FADS2 genotypes dictate the rate of omega-6 fatty acid conversion. Under high dietary omega-6 conditions, high-activity genotypes accelerate the synthesis of arachidonic acid and pro-inflammatory eicosanoids, potentially increasing cardiovascular risk, whereas low-activity carriers exhibit a metabolic plateau that limits this downstream accumulation.