Dietary interventions to prevent dementia or cognitive decline are generally safe, readily available, and can be easier to implement than interventions such as exercise. But evidence supporting these interventions varies. Perhaps the best studied is the Mediterranean diet, which is high in grains, vegetables, fruit, potatoes, nuts, seeds, legumes, fish, and olive oil, and low in red meat, poultry, dairy, and alcohol.
Source: Medscape via http://www.medscape.com/viewarticle/869379