A diet rich in olive oil, grains, vegetables and fish can lower both the risk of death and of developing chronic diseases such as heart disease, cancer and Alzheimer's, new research suggests.

A team of researchers from the University of Florence analyzed the findings of 12 international studies that included more than 1.5 million participants.

Among subjects who strictly followed a so-called Mediterranean diet, the researchers found a:

• Nine per cent drop in overall mortality;
• Nine per cent drop in mortality from heart disease;
• 13 per cent reduction in incidences of Parkinson's and Alzheimer's disease, and;
• Six per cent reduction in cancer rates.

"These results seem to be clinically relevant for public health, in particular for encouraging a Mediterranean-like dietary pattern for primary prevention of major chronic diseases," the authors conclude.

The findings are published in the online edition of the British Medical Journal.

Recent studies have suggested that following the Mediterranean diet can lower a person's risk for heart disease and cancer.

However, this is the first time a vast array of international data has been compiled and analyzed to determine how the diet may lower a person's risk of chronic disease and even death.

The Mediterranean diet is rich in olive oil, grains, fruits, nuts, vegetables and fish, but low in meat, dairy products and alcohol.

It is most common among populations in countries that border the Mediterranean Sea.

The researchers said the next step in this field of study would be to develop a so-called adherence score for the diet. This would allow doctors to recommend the diet for patients to reduce their risk of disease and then evaluate how well they are following it.