Omega-3 fats: real effects and a mixed cardiovascular picture

Omega-3 fats — EPA and DHA from oily fish, and ALA from flax and walnuts — have real biological effects and a genuinely mixed outcome literature.

Where the evidence is solid. Triglycerides fall substantially at high doses (2-4 g daily of EPA+DHA), which is a large and reproducible effect. In rheumatoid arthritis, fish oil reduces morning stiffness and joint tenderness modestly in pooled analyses.

Where it is mixed. The cardiovascular outcome trials are inconsistent. Some large trials of high-dose EPA showed a reduction in cardiovascular events; others, including large trials of EPA+DHA combinations, showed no benefit, and one meta-analysis found an association with cardiovascular outcomes that has not been replicated consistently. The reasonable position is that omega-3 is not a substitute for a statin or for risk-factor control, and that whether it helps an individual depends on what is being treated — triglycerides respond, hard outcomes are not reliably reduced.

Where it failed. Large trials of omega-3 for dementia prevention were negative despite positive observational associations. For depression, pooled analyses show a small effect, strongest for EPA-dominant preparations, with inconsistent results.

The formulation matters more than the label. What is sold as "fish oil" varies enormously in EPA+DHA content, in the ratio of the two, and in freshness. Two practical points: look at the actual EPA+DHA milligrams, not the total oil weight, and check for oxidation — rancid fish oil is a common problem and a product with a stated TOTOX value is more accountable than one without.

Contaminants and sourcing. Fish oil concentrates can carry PCBs and heavy metals depending on the source and the refining; a product with a batch analysis is preferable. Algal oil is a vegan DHA source and is chemically equivalent for DHA purposes.

The cautions. High-dose omega-3 may add to bleeding risk in people on anticoagulants or antiplatelets, and it should be stopped before surgery on advice. It can also cause GI upset, and it is a source of extra calories at therapeutic doses.

The intervention that beats a capsule. Eating oily fish two or three times a week delivers omega-3 with protein, selenium, vitamin D and iodine, and the observational evidence for fish intake is stronger than for supplements.