Previous research has shown that a Mediterranean diet - high in fruit, vegetables and fish and low in meat and dairy products - has been linked to a reduced incidence of Alzheimer's disease. Researchers from University College London studied 3,486 people with an average age of 55 taking part in a long-term study of Whitehall civil servants. They asked them about their diet and then five years later assessed them for depression. The study found that - where the average chance of developing depression was 1 - people who had a 'whole-food' diet with lots of vegetables, fruit and fish had a 0.74 chance of developing depression whereas people who consumed a processed food diet with lots of puddings, fried food, processed meat, refined grains and dairy products had a 1.58 chance of becoming depressed.
Akbaraly, Tasnime N. ... [et al] - Dietary pattern and depressive symptoms in middle age British Journal of Psychiatry November 2009, 195(5), 408-413