Public perceptions that diet influences children's behaviour are deeply ingrained, but the evidence base is flimsy. Omega-3 fatty acids are found in fish oil and there is some evidence from prisons that their inclusion in adult diets can reduce aggressive behaviour; animal evidence suggests they are important in neural development.

Research in this area is notoriously difficult because of large placebo effects and problems with blinding. American researchers working in Mauritius went to great lengths to design a rigorous study of the effects on omega-3 supplements on behaviour (Raine …