The Mediterranean diet only works if you live in a household earning £35,000 and are highly educated, a new study suggests.

Although health experts advocate a diet rich in fresh fruit, vegetables, olive oil, fish and nuts, researchers now believe that the quality of food is crucial for seeing the benefits.

Italian researchers studied the impact of a Mediterranean diet on reducing heart disease risk in 18,000 men and women over a four-year period.

In line with similar research they discovered that sticking to the plan reduced the risk of heart disease by 15 per cent, but only for people with a household income of £35,000 or higher. No actual benefits were observed for the less advantaged groups.

The researchers said the finding was surprising, and have speculated that more affluent families are able to buy better quality food which is higher in antioxidants, polyphenols and lower in pesticides.