Foods high in omega-3 — ALA and EPA/DHA are not the same thing

These are the fatty acids that build cell membranes. DHA in particular concentrates in the retina and the grey matter of the brain, which is why it matters for fetal and infant neurological development. EPA is the raw material for eicosanoids, the signalling molecules that regulate inflammation, and both reduce triglyceride production in the liver.

Omega-3 comes in three forms. ALA is found in plants — perilla, walnut, flaxseed. EPA and DHA come from oily fish and algae.

For ALA, the adequate intake is 1.6 g a day for men and 1.1 g for women. There is no official requirement for EPA and DHA, but several bodies suggest 250–500 mg a day of the two combined. Eating fish twice a week generally lands in that range.

You cannot substitute ALA for EPA and DHA by eating more of it. Conversion runs at 5–8 % to EPA and under 1 % to DHA. On a plant-based diet, DHA from algal oil is the practical answer.

Fat-soluble, so it absorbs best with a meal. It degrades with heat and oxygen — keep perilla oil refrigerated once opened and use it quickly. Rancid oil means the omega-3 is already damaged.

Fish loses more the longer and hotter it is cooked. Grilling or steaming beats deep-frying.

Expectations of supplements run ahead of the evidence. A Cochrane review of 86 randomised trials (162,796 people) found omega-3 supplementation lowered triglycerides by about 15 % (high certainty) but made essentially no difference to all-cause mortality or cardiovascular events. The authors noted that the evidence comes largely from supplement trials, with little on eating fish.

Plant ALA shows a different picture in observational work. Pooling 41 cohorts (1,197,564 people), higher ALA intake came with 10 % lower all-cause mortality (0.90, 95 % CI 0.83–0.97), and each extra gram a day with 5 % lower risk. But in the same analysis cancer mortality was 6 % higher (1.06, 1.02–1.11). These are observational studies — do not read them as cause and effect.

High-dose supplements can increase bleeding tendency, so check with a clinician if you take anticoagulants. Large fish accumulate mercury; in pregnancy, watch both the species and the frequency.