There are few simple rules to avoid the blues. One just should follow the Mediterranean diet, according to the Spanish scientists' report.
Based on "food patterns typical of Crete, much of the rest of Greece, and southern Italy in the early 1960s", this diet, in addition to "regular physical activity," emphasizes "abundant plant foods, fresh fruit as the typical daily dessert, olive oil as the principal source of fat, dairy products (principally cheese and yogurt), and fish and poultry consumed in low to moderate amounts, zero to four eggs consumed weekly, red meat consumed in low amounts, and wine consumed in low to moderate amounts". Total fat in this diet is 25% to 35% of calories, with saturated fat at 8% or less of calories.
The principal aspects of this diet include high olive oil consumption, high consumption of legumes, high consumption of unrefined cereals, high consumption of fruits, high consumption of vegetables, moderate consumption of dairy products (mostly as cheese and yogurt), moderate to high consumption of fish, low consumption of meat and meat products, and moderate wine consumption.
The Mediterranean diet usually is recommended to reduce the risk of heart attack, stroke and other cardiovascular problems. This study, reported in the October issue of the Archives of General Psychiatry, is one of only a few to assess its effect on mental function.
The Spanish researchers followed more than 10,000 healthy adults who filled out questionnaires between 1999 and 2005. All were free of depression when the trial started. Their adherence to the Mediterranean diet was measured by looking at nine components, such as low intake of meat, moderate intake of alcohol and dairy products, and high intake of fruits, nuts, cereals, vegetables and fish.
After an average follow-up of 4.4 years, the overall incidence of depression for those who most followed the diet was 30 % lower than for those who most ignored the dietary rules. Even lower rates of depression were associated with intake of specific elements of the Mediterranean diet, such as fruits, vegetables and olive oil.
There are several possible explanations for the reported protective effect. The Mediterranean diet improves the function of the endothelium, the delicate inner lining of blood vessels, which is involved in the production of brain-derived neurotrophic factor (BDNF), a molecule that is responsible for the growth and function of nerve cells.
In addition, olive oil improves the binding of serotonin to its receptors and serotonin is a key neurotransmitter in depression.
And the omega-3 fatty acids found in some fish might help improve the function of the central nervous system, Martinez-Gonzalez said. "All these mechanisms may lead to an improved brain function and a greater resilience to better face the frustrations of every day, to control stress, and so on," he said.
But researchers do not recommend that people diagnosed with depression try to treat it by adopting this diet. "The Mediterranean diet might be ideal for the prevention of depression, but not for its treatment," they said. "For those patients who already have depression, the best thing they can do is to seek the proper medical treatment by a psychiatrist."
U.S. News and World Report contributed to the report.