Omega-3 (EPA/DHA), honestly

EPA and DHA are essential fats your body can’t make well. The clearest effect is on blood triglycerides; the cardiovascular story is more nuanced than the fish-oil marketing suggests. Food first, supplement to fill a gap.

What they are

Omega-3s EPA and DHA come from oily fish and algae. DHA is a major structural fat in the brain and eyes; EPA is more anti-inflammatory. ALA (from flax/walnuts) is a plant omega-3 the body converts poorly to EPA/DHA.

Where the EPA+DHA actually comes from

Where the EPA+DHA actually comes from — an illustrative chart on this page. Figures use honest, cited or clearly-illustrative data; they are visual aids, not personal measurements.

What the evidence shows

• Lowers blood triglycerides — The clearest, most reliable effect — dose-dependent, especially useful when triglycerides are high. (established)
• Cardiovascular benefit is dose- and population-dependent — High-dose purified EPA cut cardiovascular events in high-risk people already on statins (REDUCE-IT). But general low-dose fish-oil supplements in already-healthy people showed little benefit in large trials — the truth is in between the "does nothing" and "miracle" camps. (emerging)
• Structural role in brain and eyes — DHA is a building block of the brain and retina; adequate intake (usually via fish) is linked with better cognitive and eye ageing. (established)
• Food first — Two portions of oily fish a week covers most people. Supplement mainly if you rarely eat fish or need to lower triglycerides; choose quality products to limit oxidation. (note)

What’s oversold

• “Fish oil fixes everything” — Broad claims for mood, joints and general prevention outrun the evidence, especially at the low doses in most supplements. (hype)

What we still don’t know

• Who benefits from supplements The gap between REDUCE-IT (high-dose EPA, high-risk) and null low-dose trials means the right dose, form and population are still debated.
• EPA vs DHA vs combined Whether purified EPA, DHA or a mix is best for a given goal is not fully settled.

Key terms

• EPA An omega-3 fat (eicosapentaenoic acid), more anti-inflammatory; the form used in high-dose cardiovascular trials.
• DHA An omega-3 fat (docosahexaenoic acid), a structural building block of the brain and retina.
• ALA A plant omega-3 (from flax, walnuts) that the body converts only poorly to EPA/DHA.
• Triglycerides A blood fat; high levels raise cardiovascular risk, and omega-3 reliably lowers them.