The so-called Mediterranean diet, heavy on olive oil; fish; legumes, like beans, lentils and peas; fruits, vegetables and unrefined grains; and, in moderation, low-fat dairy products, eggs and wine, has been a trendy regimen for many years, based in part on anecdotal evidence about the health and longevity of people living in the region where it originated.
But as of today, there is more definitive scientific evidence than ever before of the diet's benefits. According to a study published online by The New England Journal of Medicine, the Mediterranean diet can help prevent 30 percent of heart attacks, strokes and heart disease death for people at high risk of those conditions.
The study is being acknowledged as the first substantial clinical trial of the diet's impact on heart disease risks, and experts immediately praised its methods and results. "The really important thing — the coolest thing — is that they used very meaningful endpoints," Rachel Johnson, a professor of nutrition at the University of Vermont who chairs the American Heart Association's nutrition committee, told The New York Times. "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."
The study, led by Dr. Ramon Estruch, professor of medicine at the University of Barcelona, took place in Spain and involved about 7,500 adults with such risk factors for heart disease as obesity, a smoking habit or diabetes. Subjects were assigned either the Mediterranean diet or a low-fat diet. Those asked to follow the Mediterranean diet were divided into two groups. One group was specifically asked to add more olive oil to their diets, and the other was given the same instruction regarding nuts. Researchers then tracked their compliance through regular blood and urine tests to detect biomarkers of each food, the anti-inflammatory compound hydroxytyrosol for olive oil and alpha-linolenic acid for nuts. The Mediterranean diet groups were also asked to eschew cookies, cakes and pastries and to limit consumption of processed meats.
Researchers provided nutritional counseling to all participants, but found that the adults they had asked to follow the low-fat diet had a much harder time sticking to the regimen than those assigned the Mediterranean diet. In the end, the researchers noted, they were in many cases comparing the Mediterranean diet not to a low-fat diet but to a standard modern one.
And as results came in, researchers actually decided to halt the study early, after five years, because the findings were so conclusive they determined it was unethical to continue having some participants continue to take part in the control group.
Given what had previously been mostly an anecdotal basis for following the diet, some heart-disease experts had been skeptical of its potential effect, especially among people already taking drugs to limit their risk. In the Spanish study, many of the subjects were already taking statins or other drugs to lower blood pressure or manage diabetes, making their pronounced drop in cardiac risk all the more impressive. "This is actually really surprising to us," Estruch said.
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Other experts, while acknowledging the potential benefits of the Mediterranean diet, had resisted advising patients to follow it because some of its building blocks, like nuts and oils, are high in calories. Indeed, subjects in the new study did not necessarily lose weight on the diet, but as Johnson told The Boston Globe, "We have moved away from the low-fat-at-all-cost message. It's important to include these healthy fats in a diet."
The study supports that message. No research has yet found low-fat diets to have a significant impact on heart risks. They are also, of course, difficult for many adults to follow. "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, and you can actually enjoy life," Dr. Steven Nissen, chair of the department of cardiovascular medicine at the Cleveland Clinic Foundation, told the Times.
The study did not measure the effect of the Mediterranean diet on people without heart-disease risks, but Estruch said he believes it would help such people as well, especially if it was followed as a lifelong approach to nutrition. He said that many members of his team switched to the Mediterranean diet as they saw results come into their labs.