A Mediterranean diet could stave off depression as well as heart disease, suggests new research.

The study, involving more than 15,000 people, shows a diet loaded with fruit, vegetables, beans and nuts and olive oil, with low levels of processed meats, could prevent the onset of depression.

Researchers, whose findings were published in the journal BMC Medicine, looked at the impact of three major diets on mental health: the Pro-vegetarian Dietry Pattern; the Alternative Healthy Eating Index-2010 and the Mediterranean diet.

Meat, sweets and other sources of animal fats and trans and saturated fatty acids scored low, while nuts, fruits, veg and other sources of omega-4 fatty acids, vitamins and minerals, scored highly.

Ten years alter, the participants were asked to complete another survey on their diets.

A total of 1,550 participants reported a clinical diagnosis of depression or had used antidepressant drugs since the study began.

The Alternative Healthy Eating Index-2010 was found to be the associated with the greatest reduction of the risk of depression, but most of its effect could be associated with the major elements of the Mediterranean Diet.

So scientists say common nutrients and food items such as omega-3 fatty acids, vegetables, fruits, beans, nuts and moderate alcohol intake present in both patterns could be responsible for cutting the risk of depression.

Author Dr Almudena Sanchez-Villegas, from the University of Las Palmas de Gran Canaria explained the thinking behind the study.

He said: 'We wanted to understand what role nutrition plays in mental health, as we believe certain dietary patterns could protect our minds.

'These diets are all associated with physical health benefits and now we find that they could have a positive effect on our mental health.