Well, you’d have to eat 36 cups of walnuts just to ingest as much docosahexaenoic acid (DHA) – or 2 cups for as much eicosapentaenoic acid (EPA) – as 84g of Alaska salmon.
That’s because plant sources of omega-3 contain a different type of fat, called alpha-linolenic acid (ALA). “This is the parent fatty acid of EPA and DHA, but most people don’t metabolise ALA efficiently,” says Dr Artemis Simopoulos, author of The Omega Diet.
In fact, less than 5 per cent of the ALA you eat is converted into EPA, and less than 1 per cent to DHA, according to a study review in the Journal of Nutrition. For a bona fide fish substitute, go with an omega-3 supplement that delivers about 500mg each of EPA and DHA.