Since what people eat -– the nutrients available to the body -– affects various bodily functions, it seems logical that diet would affect brain chemistry and mood as well. Diet decisions that improve the rest of the body may improve the brain’s outlook on the world.

When people are feeling better by dieting and losing weight or resolving symptoms that they’re having, that could have an impact on mood. When people engage in healthy lifestyle changes, there are improvements in depression.

Nutrition also influences the immune system, which has been shown to influence the risk of depression, as well. 

It could also come down to inflammation. A study published in January gave more support to the theory that increased inflammation in the body could play a role in depression. The study found that people who had depression had 46% higher levels in their blood samples of of C-reactive protein (CRP), a marker of inflammatory disease.

Diets like DASH and the Mediterranean Diet -- another brain-healthy diet with a focus on foods like olive oil, fish and vegetables -- are both rich in anti-inflammatory foods.

Foods like white bread, margarine, red meat, processed meat and fried foods can cause inflammation in the body and should be eaten minimally or avoided, according to Harvard Medical School.

Tomatoes, olive oil, green leafy vegetables, nuts, fish like salmon and sardines and fruits like oranges and strawberries are all foods that fight inflammation.

Although the determinants of mental health are complex, the emerging and compelling evidence for nutrition as a crucial factor in the high prevalence and incidence of mental disorders suggests that diet is as important to psychiatry as it is to cardiology, endocrinology, and gastroenterology.