Sir

SIR — The mackerel pictured in A. K. Duttaroy's review of Susan Allport's book Queen of Fats (Nature 444, 425; doi:10.1038/444425a2006) are indeed a source of omega-3s, but others are just as good and more sustainable. Early humans evolved eating fish, probably inter-tidal shellfish, while living a shoreline existence in Africa. They didn't have boats to trawl for pelagic oily fish such as mackerel, nor did they have hooks and lines. Now, as then, inter-tidal herbivorous shellfish such as mussels and clams can help people reach a healthy 1:1 balance of omega-3 and omega-6 fats in their diets, instead of the current 1:17.