A woman buys fruit at a market in Barcelona, Spain. Mediterranean diets have long been touted as heart-healthy, but that's based on observational studies. Now, one of the longest and most scientific tests suggests this style of eating can cut the chance of suffering heart-related problems. (Emilio Morenatti/AP)

The “Mediterranean diet,” featuring vegetables, fruits, fish, nuts and olive oil but almost no red meat or sweets, slightly reduces the risk of cardiovascular disease. Most of the effect was seen in a reduction in strokes.

That is the conclusion of a five-year diet experiment conducted in Spain, the results of which were revealed Monday at a meeting in California.

While the benefit was small, this route to better health was without risk or side effects — and included wine.

“Usually doctors tell you not to do pleasant things,” said Miguel Angel Martinez-Gonzalez, a physician at the University of Navarre who headed the study. “But this is very tasty and easy to follow. You do not need to suffer for the Mediterranean diet.”

The experiment compared three different diets in people at higher-than-normal cardiovascular risk. (Half had Type 2 diabetes, and about 80 percent had hypertension). All of the diets were significantly different from what most Americans eat.

For example, virtually everyone in the Spanish study used olive oil as their main culinary fat, ate less than one serving of red meat a day and had at least one meatless day a week. Two-thirds ate fish three times a week. Almost everyone had less than one soft drink a day, and nearly three-quarters had fewer than two baked sweets a week.

How such a diet might affect health in the United States is uncertain. It is possible the benefits might be even greater.

The benefit of the Mediterranean diet was first recognized more than 50 years ago by Ancel Keys, a physiologist at the University of Minnesota who compared rates of heart disease in seven countries with different diets.

In the new study, about 7,500 people, most in their 60s, were randomly assigned either one of two Mediterranean diets or a control diet.

People in the Mediterranean ­diets were advised to emphasize olive oil, nuts, fresh fruits and vegetables, fatty fish, poultry instead of red meat, a sauce called “sofrito” (made by simmering herbs, garlic, tomatoes and oil together), and red wine with dinner if they drank alcohol. An incentive to use important dietary constituents, one group was given a quart of extra-virgin olive oil and the other a half-pound of nuts (mostly walnuts) each week.

People assigned to the control diet got slightly different advice. Lean fish, pasta and bread were recommended, and olive oil, nuts and sofrito were discouraged. They received small non-edible gifts but no free food.

The researchers looked at numerous health outcomes, the main one being a combination of heart attack or stroke or cardiovascular death (measured as the number of events per 1,000 years spent consuming each diet). In the two Mediterranean diets there were eight events, compared with 11 in the control diet — a reduction of about 30 percent.

When the researchers examined the events, the most dramatic decline was in the rate of stroke in the Mediterranean diet groups. The rates of heart attack and death were slightly lower too, but not significantly so in statistical terms. With a larger or longer study, it’s possible a clear reduction in those outcomes might have emerged.

The Mediterranean diet added to cardiovascular benefits the participants were getting elsewhere. Forty percent were taking cholesterol-lowering statin drugs, and 20 percent were on aspirin. About 30 percent of people drank at least a glass of wine a day — a habit also known to protect against heart attack.

The Mediterranean diet proved beneficial even though the people on the control diet cut their calories over the five-year experiment. At the end, they were consuming 1,960 calories a day, compared with about 2,200 for those on the Mediterranean diet.

The study, called Predimed, was presented at the Sixth International Congress on Vegetarian Nutrition at Loma Linda University in California. It was published online by the New England Journal of Medicine.

Martinez-Gonzalez said he and his colleagues are about to start a new study involving 7,000 people in which everyone will consume a Mediterranean diet (with both oil and nuts especially recommended). Half the people will be randomly assigned to add three other interventions to their diet — a target for daily calories, a target body weight and a minimum amount of exercise.

The goal is to see whether, and by how much, that might further reduce cardiovascular disease.