About 30 percent of heart attacks, strokes and deaths from heart disease can be prevented in people at high risk if they switch to a Mediterranean diet rich in olive oil, nuts, beans, fish, fruits and vegetables, and even drink wine with meals, a large and rigorous new study has found.
The findings, published Monday on The New England Journal of Medicine's website, were based on the first major clinical trial to measure the diet's effect on heart risks. The magnitude of the diet's benefits startled experts. The study ended early, after almost five years, because the results were so clear that it was considered unethical to continue.
The diet helped those following it, even though they did not lose weight and most of them were already taking statins or blood pressure or diabetes drugs to lower their heart disease risk.
"Really impressive," said University of Vermont nutrition professor Rachel Johnson, an American Heart Association spokeswoman. "And the really important thing, the coolest thing, is that they used very meaningful end points. They did not look at risk factors like cholesterol or hypertension or weight. They looked at heart attacks and strokes and death. At the end of the day, that is what really matters."
Until now, evidence that the Mediterranean diet reduced the risk of heart disease was weak, based mostly on studies showing that people from Mediterranean countries seemed to have lower rates of heart disease -- a pattern that could have been attributed to factors other than diet.
Some experts had been skeptical that the diet's effect could be detected, if it existed at all, because so many people are already taking powerful drugs to reduce heart disease risk. Other experts hesitated to recommend the diet to those who already had weight problems because oils and nuts have a lot of calories.
Heart disease experts said the study was a triumph because it showed that a diet was powerful in reducing heart disease risk, and it did so using the most rigorous methods. Scientists randomly assigned 7,447 people in Spain who were overweight, were smokers, or had diabetes or other risk factors for heart disease to follow the Mediterranean diet or a low-fat one.
Low-fat diets have not been shown in any rigorous way to be helpful, and they are also very hard for patients to maintain -- a reality borne out in the new study, said Steven E. Nissen, chairman of the Cleveland Clinic Foundation's department of cardiovascular medicine. "Now, along comes this group and does a gigantic study in Spain that says you can eat a nicely balanced diet with fruits and vegetables and olive oil and lower heart disease by 30 percent," Dr. Nissen said. "And you can actually enjoy life."
The study by University of Barcelona professor of medicine Ramon Estruch and his colleagues was long in the planning. The investigators sought advice around the globe on how best to answer the question of whether a diet alone could make a big difference in heart disease risk.
In the end, they decided to randomly assign subjects at high heart disease risk to three groups. One would be given a low-fat diet and counseled on how to follow it. The other two groups would be counseled to follow a Mediterranean diet.
At first, the Mediterranean dieters got more intense support, meeting regularly with dietitians. The low-fat group just got an initial visit to train them in how to adhere to the diet, followed each year by a leaflet on the diet. Then researchers decided to add more intensive counseling for them, too, but they still had difficulty staying with the diet.
One group assigned to a Mediterranean diet was given extra virgin olive oil each week and instructed to use at least 4 tablespoons a day. The other group got a combination of walnuts, almonds and hazelnuts and was told to eat about an ounce of the mix each day.
The diet mainstays consisted of at least three fruit servings and at least two of vegetables daily. Participants were to eat fish at least three times a week and legumes -- beans, peas and lentils -- at least three times a week. They were to eat white meat instead of red, and, for those accustomed to drinking, to have at least seven glasses of wine a week with meals.
To assess compliance with the Mediterranean diet, researchers measured levels of a marker in urine of olive oil consumption -- hydroxytyrosol -- and a blood marker of nut consumption -- alpha-linolenic acid. Participants stayed with the Mediterranean diet, investigators reported. But those assigned a low-fat diet did not lower their fat intake much.
Dr. Estruch said he thought the the Mediterranean diet's effect was because of the entire package, not just the olive oil or nuts. He didn't expect to see such a big effect so soon.
Researchers were careful to say in their paper that while the diet clearly reduced heart disease for those at high risk, more research was needed to establish its benefits for those at low risk.
Not everyone is convinced, though. Caldwell Blakeman Esselstyn Jr., author of the best-seller "Prevent and Reverse Heart Disease: The Revolutionary, Scientifically Proven, Nutrition-Based Cure," who promotes a vegan diet and does not allow olive oil, dismissed the new study.