A Spanish study revealed that people who are on a Mediterranean diet, which includes an eating regime rich in fruits, vegetables, whole grains, fish and nuts, were less likely to develop depression.

Study co-author Dr. Miguel A. Martinez-Gonzalez, chair of preventive medicine at the University of Navarra said, "We are speaking of a relative reduction in risk of 42 percent to 51 percent, there is a strong association".

The Mediterranean diet usually is recommended to reduce the risk of heart attack, stroke and other cardiovascular problems.

This study is one of the few which have assessed its effect on mental function.

The researchers assessed the answers of more than 10,000 adults who filled out questionnaires between 1999 and 2005. All of them were free from depression when the trial began.

After a follow up of 4.4 years, the overall incidence of depression for those who mostly followed the diet was as much as 30 percent lower than for those who ignored the dietary rules mostly.

The factors which cause the protective effect can be due to the fact that Mediterranean diet improves the function of the delicate inner lining of blood vessels, which is involved in the production of brain derived neurotrophic factor (BDNF), which is a molecule that is responsible for the growth and function of nerve cells.

Olive oil improves the binding of serotonin to it receptors and serotonin is a key neurotransmitter in depression. The omega-3 fatty acids present in some fish might help improve the function of the central nervous system.

However the Mediterranean diet can’t be treated as a treatment for depression but if you have a family history of depression and are concerned about it then this is a good place to start.