MINNEAPOLIS — A Mediterranean diet with extra servings of olive oil or mixed nuts reduced the risk of a first heart attack, stroke and death by almost 30 percent in less than five years, according to a study from Spanish researchers.

The research involved 7,477 high-risk volunteers, all of whom were diabetic or had a host of risk factors including obesity, high cholesterol, family history of heart disease or smoking. Heart damage was significantly more likely to occur in people told to watch their fat intake than in those given olive oil or nuts and told to follow a Mediterranean diet, according to the study in the New England Journal of Medicine. The study was halted after the benefits of the diet became clear, the researchers said.

The findings add more weight to the benefits of a Mediterranean diet rich in fruits, vegetables, fish and oils, the researchers said. While numerous studies show healthy eating can cut complications in people who already have heart disease and help ward off ailments including Alzheimer's disease and diabetes, the study is the first to show a diet can prevent deadly heart disease from developing.

"These results support the benefits of the Mediterranean diet for cardiovascular risk reduction," said the researchers led by Ramon Estruch from the University of Barcelona. "They are particularly relevant given the challenges of achieving and maintaining weight loss," they said. "The results of our trial might explain, in part, the lower cardiovascular mortality in Mediterranean countries than in northern European countries or the United States."

In the study, 3.4 percent of those on a Mediterranean diet who were given extra nuts experienced a heart attack, stroke or died from cardiac complications, compared with 3.8 percent on a Mediterranean diet plus extra olive oil and 4.4 percent of those asked to follow a low-fat diet. No one was told to curtail their calories or assigned an exercise program.

Recommended foods in the Mediterranean diet were olive oil, nuts, fruits and vegetables, fish, legumes, a mix tomato, onion and garlic, and wine with meals. Soda, baked goods, spreads and red or processed meats were discouraged. Those in the comparison group were encouraged to eat low-fat dairy products, bread, potatoes, pasta or rice, fruits and vegetables, lean fish and seafood, and told to avoid vegetable oil, baked goods, nuts, red meat, fatty fish, spreads and the mix of tomato, onion and garlic known as sofrito.

The study was funded by the Spanish government's Instituto de Salud Carlos III.