The authors, from the universities of Las Palmas and Navarra, assess the evidence into links between diet and depression and find it lacking. ”Depression is similar in many aspects to heart disease” they explained. “Both are associated with low-grade inflammation, endothelial dysfunction and worse lipid profiles. This tends to suggest that the underlying causes, such as a diet high in trans fats, are also the same.”

Though there is plenty of evidence that there is an association, and that fast food increases risk of depression (while the Mediterranean diet decreases it), most of these studies do not show causality. Almudena Sanchez-Villegas continued, “It is difficult to be sure that the diet is responsible for depression – it could be that depressed people make bad food choices. Other study problems include ‘confounders’ which may influence dietary habits, such as marital status, exercise, alcohol (or smoking), medical conditions and social networks. Or simply genetics.”

Miguel A Martínez-González concluded, “To address these issues we need long term, randomised clinical studies similar to ones successfully conducted for diet and cardiovascular disease risk. Only then will we really understand the impact of diet of depression.”