Omega-3 Fatty Acids: ALA, EPA, and DHA

The Omega-3 Family: ALA, EPA, and DHA

Omega-3 fatty acids are a family of polyunsaturated fats sharing a defining structural feature: a carbon-carbon double bond at the third carbon from the methyl (omega) end of the fatty acid chain. They are classified as essential fatty acids because the human body cannot synthesize them de novo — they must be obtained through diet.

Three omega-3s dominate the nutritional literature:

• Alpha-linolenic acid (ALA) — the plant-based omega-3, found in flaxseeds, chia seeds, walnuts, hemp seeds, and canola oil. ALA is the parent omega-3; the body can convert it to EPA and then DHA, but this conversion is inefficient: only about 5–10% of ALA converts to EPA and less than 1% converts to DHA.
• Eicosapentaenoic acid (EPA) — a 20-carbon omega-3 with potent anti-inflammatory effects. Found primarily in marine sources (fatty fish, algae).
• Docosahexaenoic acid (DHA) — a 22-carbon omega-3 that is the predominant structural fat in the brain (about 97% of brain omega-3s), retina (93% of retinal polyunsaturated fat), and heart. DHA is also found primarily in marine sources and is the most critical omega-3 for brain and eye development.

The Adequate Intake (AI) for ALA is 1.6 g/day for men and 1.1 g/day for women. There is no formal RDA for EPA or DHA, but most health authorities recommend 250–500 mg combined EPA+DHA per day for adults, and 200 mg DHA/day for pregnant and breastfeeding women.

Anti-Inflammatory Mechanisms

Omega-6 fatty acids (primarily linoleic acid, found in most vegetable oils) and omega-3 fatty acids compete for the same elongase and desaturase enzymes in the body. The modern Western diet has an omega-6 to omega-3 ratio of approximately 15:1 to 17:1, compared to an estimated ancestral ratio of 4:1 or lower.

This matters because omega-6 metabolism produces arachidonic acid (AA), which is the precursor to pro-inflammatory eicosanoids (prostaglandins, thromboxanes, leukotrienes). EPA, by contrast, produces anti-inflammatory eicosanoids (E3-series prostaglandins, E5-series leukotrienes). DHA is converted to resolvins and protectins — specialized pro-resolving mediators that actively resolve inflammation.

Increasing dietary EPA and DHA shifts the eicosanoid balance toward resolution of inflammation. This is the mechanistic basis for omega-3s' cardiovascular, joint, and anti-inflammatory benefits observed in clinical research.

Food Sources of Omega-3 Fatty Acids

Algal oil is the primary vegan source of pre-formed EPA and DHA. It is derived from the same microalgae that produce these fatty acids in fish (fish do not synthesize omega-3s themselves; they bioaccumulate them by eating algae and smaller fish). Algal oil supplements bypass the inefficient ALA conversion pathway and avoid concerns about marine pollutants.

Cardiovascular and Brain Health Evidence

Cardiovascular effects of EPA and DHA are among the best-studied nutritional interventions:

• Triglycerides: High-dose EPA+DHA (2–4 g/day) reduces serum triglycerides by 20–30%, an effect comparable to prescription fibrates. This is the basis for FDA-approved omega-3 pharmaceutical products (icosapentaenoic acid at 4 g/day).
• Platelet aggregation: EPA and DHA reduce platelet stickiness, contributing to anticoagulant effects. At supplemental doses, this may increase bleeding time slightly — clinically relevant before surgery.
• Blood pressure: Meta-analyses find modest reductions in systolic and diastolic blood pressure (approximately 1.5–3 mmHg) with omega-3 supplementation.
• Cardiac arrhythmias: DHA stabilizes cardiomyocyte membranes. Epidemiological data link higher EPA+DHA status with lower rates of sudden cardiac death.

Brain and cognitive health: DHA constitutes approximately 8% of brain dry weight. Lower DHA status is associated with accelerated cognitive decline and increased Alzheimer's risk in observational studies. DHA supplementation during pregnancy and early childhood is consistently associated with better neurodevelopmental outcomes. Evidence for benefit in preventing cognitive decline in adults without deficiency is less consistent.

Supplements and Practical Considerations

Fish oil supplements are the most common omega-3 source, typically providing 180 mg EPA and 120 mg DHA per standard 1,000 mg capsule — though "triple-strength" or concentrated products can provide 900 mg EPA+DHA per gram. Key considerations:

• Oxidation: Omega-3 fatty acids are highly susceptible to oxidation, which reduces potency and may produce harmful byproducts. Choose supplements that are third-party tested, stored properly (refrigerated after opening), and smell fresh — rancid fish oil has a sharp, unpleasant odor rather than the mild ocean smell of fresh product.
• Form: Triglyceride (TG) form is better absorbed than ethyl ester (EE) form; phospholipid form (found in krill oil) may also have superior bioavailability. Taking supplements with a fat-containing meal further improves absorption.
• Drug interactions: At doses above 3 g/day, omega-3s may enhance the effect of anticoagulant medications (warfarin, aspirin). Consult a healthcare provider if taking blood thinners.
• Mercury concerns: Fish oil supplements are typically purified and contain negligible mercury. Whole fish is also generally safe; the FDA's guidance for vulnerable populations (pregnant women, young children) recommends 2–3 servings per week of lower-mercury fish.