Do higher arachidonic-acid-to-EPA and omega-6-to-omega-3 ratios favor a more inflammatory balance, and does FADS1 rs174547 affect inflammatory lipid mediator availability?

Clinical and metabolic evidence

• Substrate competition and eicosanoid balance: Arachidonic acid (AA) and eicosapentaenoic acid (EPA) compete for the same cyclooxygenase (COX) and lipoxygenase (LOX) enzymes. High membrane ratios of AA to EPA, driven by elevated dietary omega-6 to omega-3 intake, bias enzymatic pathways toward synthesizing highly active series-2 prostaglandins (e.g., PGE2) and series-4 leukotrienes (e.g., LTB4) over less inflammatory series-3 prostaglandins and series-5 leukotrienes.
• Systemic inflammatory markers: Elevated AA:EPA and omega-6:omega-3 ratios are positively associated with elevated levels of circulating interleukin-6 (IL-6), a key driver of systemic cytokine signaling. Lowering these ratios through omega-3 supplementation has been shown to downregulate these inflammatory lipid milieus and decrease IL-6 levels.

Mechanistic explanations

• Genetic regulation of LC-PUFA metabolism: The FADS1 gene encodes the delta-5 desaturase (D5D) enzyme, which catalyzes the rate-limiting step converting dihomo-γ-linolenic acid (DGLA) to AA, and eicosatetraenoic acid to EPA.
• Impact of rs174547 polymorphism: Carrying the minor C allele of the FADS1 rs174547 variant significantly decreases D5D expression and enzymatic activity. This impairment results in a accumulation of upstream precursor fatty acids (such as linoleic acid and alpha-linolenic acid) and a substantial reduction in downstream long-chain polyunsaturated fatty acids (LC-PUFAs), particularly AA and EPA.
• Substrate pool depletion: Because AA and EPA serve as the primary baseline substrate pools for COX, LOX, and cytochrome P450 pathways, the rs174547-driven reduction in these fatty acids severely limits the endogenous availability and generation of both pro-inflammatory eicosanoids and specialized pro-resolving mediators (such as resolvins and protectins).

Bottom line

A higher AA:EPA and omega-6:omega-3 ratio shifts the cellular environment toward a pro-inflammatory eicosanoid and cytokine profile. This metabolic pathway is heavily modulated by the FADS1 rs174547 polymorphism; individuals carrying the minor allele have genetically reduced delta-5 desaturase activity, which significantly lowers their endogenous synthesis of AA and EPA, thereby altering the baseline substrate availability for downstream inflammatory and resolving lipid mediators.