About 30 percent of heart attacks, strokes and heart disease deaths can be prevented in people with high risk factors if they switch to a Mediterranean diet rich in olive oil, nuts, beans, fish, fruits, vegetables and even wine with meals, according to a large and rigorous new study.
The findings, published Monday in the New England Journal of Medicine, were based on the first major clinical trial to measure the heart effects of the diet, whose fans have long promoted it as healthy.
The magnitude of the diet’s benefits startled experts. In fact, the study was 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 even though most of them were already taking statins or blood pressure or diabetes drugs to lower their risks.
“Really impressive,” said Rachel Johnson, a professor of nutrition at the University of Vermont and a spokeswoman for the American Heart Association.
“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 for the Mediterranean diet was weak, based mostly on studies showing that people from Mediterranean countries seemed to have lower rates of heart disease, a pattern that could stem from factors other than diet.
And some experts had been skeptical that the effect of diet could be detected, if it existed at all, because so many people were already taking powerful drugs to reduce heart disease risk. Other experts hesitated to recommend the diet to people who had weight problems, because oils and nuts contain a lot of calories.
Heart disease experts said the study was a triumph because it showed that the diet is powerful in reducing risk and did so using the most rigorous methods. Scientists randomly assigned 7,447 people in Spain who were overweight, smoked and had diabetes or other risk factors for heart disease to follow the Mediterranean diet or a very low-fat one.
Very low-fat diets have not been shown in any rigorous way to be helpful, and they are hard to stick to.
“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,” said Dr. Steven Nissen, chairman of cardiovascular medicine at the Cleveland Clinic Foundation. “And you can actually enjoy life.”
The study, led by Dr. Ramon Estruch, a professor of medicine at the University of Barcelona, was long in the planning.
The researchers decided to randomly assign the high-risk subjects to three groups. One would be given a low-fat diet and counseled on how to follow it.
The two other groups would be counseled to follow a Mediterranean diet, with one group instructed to consume at least 4 tablespoons of extra-virgin olive oil a day, while the other Mediterranean diet group was told to eat about an ounce of walnuts, almonds and hazelnuts a day. An ounce of walnuts is about a generous handful.
The mainstays of the diet: At least three servings a day of fruits and at least two servings of vegetables. Fish at least three times a week. Legumes, which include beans, peas and lentils, at least three times a week. White meat instead of red. And for those accustomed to drinking, at least seven glasses of wine a week with meals.
The Mediterranean eaters were encouraged to avoid commercially made cookies, cakes and pastries and to limit their consumption of dairy products and processed meats.
To assess compliance, researchers measured levels of a marker in urine of olive oil consumption — hydroxytyrosol — and a blood marker of nut consumption — alpha-linolenic acid.
The participants stuck with the Mediterranean diet, the investigators reported. But those assigned to the very low-fat diet did not lower their fat intake much. So the study wound up comparing the usual modern diet, with its regular consumption of red meat, soft drinks and commercial baked goods, to a diet that shunned all that.
Estruch said he thought the effect of the Mediterranean diet was because of the entire package, not just the olive oil or nuts. But he said he did not expect to see such a big effect so soon.
“This is actually really surprising to us,” he said.
Not everyone is convinced, though.
Dr. 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 report.
Esselstyn said participants in the Mediterranean diet study still had heart attacks and strokes. So the study just showed that “the Mediterranean diet and the horrible control diet were able to create disease in people who otherwise did not have it,” he said.
Others hailed the study.
“This group is to be congratulated for carrying out a study that is nearly impossible to do well,” said Dr. Robert Eckel, a professor of medicine at the University of Colorado and past president of the American Heart Association.
As for the researchers themselves, Estruch said, many have changed their own diets and are following a Mediterranean one.
“We have all learned,” he said.