Food · lesson 8 of 12
Omega-3 (EPA & DHA) — fats that act like nutrients
Anti-inflammatory fats for brain and heart, the ALA conversion problem, the omega-3 index, and fish vs algae.
7 min read · reviewed October 2026
Omega-3s are fats, but they behave like micronutrients: tiny structural and signaling roles with outsized effects. The two that matter most are EPA and DHA, the long-chain omega-3s found in fatty fish.
DHA is a literal building block of your brain and the retina of your eye — it's a major structural fat in neural cell membranes. EPA is the bigger player in calming inflammation. Both are "essential" in the practical sense: your body can't make enough on its own.
How omega-3s calm inflammation
Omega-3s get built into your cell membranes and become the raw material for signaling molecules that turn inflammation DOWN — partly by displacing omega-6 fats that tend to turn it up.
How it works →
EPA and DHA incorporate into the phospholipids of every cell membrane. From there they're converted into specialized pro-resolving mediators (resolvins, protectins) that actively switch OFF inflammation once a threat has passed. They also compete with arachidonic acid (an omega-6) for the same enzymes (COX, LOX), shifting the balance of eicosanoids toward less inflammatory signaling. More omega-3 in the membrane = a calmer baseline inflammatory tone.
What the studies show →
The strongest randomized evidence is for triglyceride lowering (high-dose EPA/DHA reliably cuts blood triglycerides) and for cardiovascular risk in specific high-dose, high-risk settings. Broad supplementation in well-nourished, low-risk people shows smaller and less consistent effects. The brain/cognition story is biologically strong but clinically mixed — again, the clearest benefit is in people starting low (e.g. those eating little fish).
Roughly what percent of plant-based ALA omega-3 does the body convert into the active EPA, and even less into DHA?
Somewhere between 1 and 50 %.
Reveal the answer →
~5–10% to EPA, often <1–5% to DHA
ALA (the omega-3 in flax, chia, walnuts) must be elongated into EPA and DHA, and that conversion is inefficient — typically only ~5–10% reaches EPA and often under 5% (sometimes <1%) reaches DHA, with conversion lower in men. So while ALA foods are healthy, they're an unreliable way to raise DHA. Direct EPA/DHA from fish or algae is far more efficient.
Where omega-3s come from
Salmon, sardines, mackerel, anchovies, herring — the gold standard, delivering preformed EPA and DHA your body can use directly. Two servings of fatty fish per week is the common dietary target. Smaller fish (sardines, anchovies) carry less accumulated mercury.
Fish get their omega-3 from algae — you can go to the source. Algae oil supplements deliver DHA (and increasingly EPA) directly, making them the reliable vegan/vegetarian route, bypassing the poor ALA conversion entirely.
Flaxseed, chia, walnuts, hemp deliver ALA, which converts only weakly to EPA/DHA. Genuinely healthy foods, but don't rely on them alone to hit DHA — pair with fish or algae if DHA is the goal.
DHA, the brain, and the fish-vs-algae question
DHA is a structural fat your brain and eyes are partly built from, and you can get it straight from fish or — since fish get it from algae — from algae oil. Plants like flax only give the precursor, which converts poorly.
How it works →
DHA is one of the most abundant fatty acids in neuronal membranes and the retina, where it keeps membranes fluid and supports the function of embedded receptors and ion channels. Marine algae are the original producers of EPA and DHA; fish accumulate them by eating algae (or smaller fish that ate algae). So algae-oil supplements deliver preformed DHA directly, sidestepping the inefficient ALA→DHA conversion that limits plant sources.
What the studies show →
DHA's structural role in the developing brain underpins the recommendation for adequate omega-3 in pregnancy and infancy. In adults, observational data tie higher omega-3 intake/status to better cognitive aging, though randomized trials are mixed and most convincing in people who started with low intake. Algae-derived DHA has been shown to raise blood DHA comparably to fish-derived sources, validating it as a genuine vegan equivalent.
The omega-3 index
The best status marker isn't a food diary — it's the omega-3 index, the percentage of EPA + DHA in your red blood cell membranes. Below ~4% is considered high-risk; ~8%+ is the proposed optimal target. It reflects your long-term intake (membranes turn over slowly), unlike a single blood-fat reading, and is the closest thing omega-3 has to a 25-OH-D-style test.
Browse which fish and plant foods deliver the most omega-3 — and lean on oily fish a couple of times a week before reaching for a capsule.
Why are flax and chia an unreliable way to raise DHA?
- They contain no omega-3 at all
- Their ALA omega-3 converts only weakly into EPA and especially DHA
- DHA is destroyed by cooking these seeds
- They contain omega-6 instead of omega-3
Show the answer →
B.Their ALA omega-3 converts only weakly into EPA and especially DHA
Flax, chia and walnuts provide ALA, which the body must convert to EPA and DHA — and that conversion is inefficient (often <5% reaches DHA). They're healthy foods, but for DHA specifically, fish or algae oil is far more reliable.