LONDON (Reuters) – A Mediterranean diet rich in fruits and vegetables — already known to protect against heart disease — also appears to help ward off diabetes, Spanish researchers said on Friday.

The study published in the British Medical Journal showed that people who stuck closely to the diet were 83 percent less likely to develop type 2 diabetes than those who did not.

“The new thing is that we have been able to assess adherence to a Med diet and the incidence of diabetes in people who were initially healthy,” said Miguel Martinez-Gonzalez, an epidemiologist at the University of Navarra in Spain, who led the study. “We didn’t expect such a high reduction.”

The World Health Organisation estimates more than 180 million people worldwide have diabetes — a number likely to more than double by 2030 as more nations adopt a Western lifestyle.

Type 2 diabetes accounts for 90 percent of all cases and is closely linked to obesity and heart disease. The condition accounts for an estimated 6 percent of all global deaths.

For their study the Spanish researchers recruited 13,000 former students at the university with an average age of 38 who had no history of diabetes. They tracked their dietary habits and health over an average four years.

The volunteers also initially completed a food frequency questionnaire to measure the kinds of food they ate. The list included questions on the use of fats and oils, cooking methods and dietary supplements.

People who strictly adhered to a Mediterranean diet full of vegetables, fish and healthy fats such as olive oil, and low in red meat, dairy products and alcohol had lower odds of diabetes.

Only about 40 people in the study developed diabetes but Martinez-Gonzalez added in a telephone interview that further study is needed to confirm the diet’s protective effects.

But the fact that the protection appeared to extend to older people, smokers and volunteers with a family history of diabetes — a group all the more prone to the disease — shows the diet works, Martinez-Gonzalez said in a telephone interview.

“These higher risk participants with better adherence to the diet, however, had a lower risk of diabetes, suggesting that the diet might have a substantial potential for prevention,” the researchers wrote.