Can reduced EPA availability and arachidonic acid dominance keep the AA/EPA ratio high?

The balance between membrane-bound omega-6 and omega-3 fatty acids is a primary driver of systemic inflammatory tone. At the center of this dynamic is the ratio of arachidonic acid (AA) to eicosapentaenoic acid (EPA) within cellular membranes.

Cellular and enzymatic mechanisms

• Enzymatic competition: AA and EPA compete directly for the same cyclooxygenase (COX), lipoxygenase (LOX), and cytochrome P450 (CYP) enzymes.
• Mediator shift: An elevated AA-to-EPA ratio shifts downstream metabolism toward pro-inflammatory 2- and 4-series eicosanoids (such as PGE2 and LTB4) while suppressing the synthesis of weaker 3- and 5-series counterparts and anti-inflammatory E-series resolvins.

Genetic and dietary conversion bottlenecks

• Desaturase impairment: Genetic polymorphisms in the FADS1/FADS2 gene cluster, such as the minor alleles of rs174547 or rs174537, limit delta-5 and delta-6 desaturase activity, creating a bottleneck in endogenous EPA synthesis.
• Dietary competition: Excess dietary linoleic acid (LA) competes for these same rate-limiting enzymes, further reducing the conversion of alpha-linolenic acid (ALA) to EPA by up to 40%.

Inflammatory amplification

• Substrate release: When inflammatory pathways are activated, phospholipases cleave fatty acids from membrane pools. Under conditions of AA dominance, this enzymatic cleavage selectively floods pathways with AA, compounding the synthesis of pro-inflammatory mediators and reinforcing chronic cellular inflammation.

Bottom line

• Inherited genetic bottlenecks in the FADS1/FADS2 pathway and high dietary omega-6 intake interact to severely restrict EPA availability and drive AA dominance. Under active inflammatory demand, this skewed ratio favors the synthesis of pro-inflammatory eicosanoids over pro-resolving mediators, sustaining a chronic pro-inflammatory state.