Finally, there's hard evidence that a Mediterranean diet can prevent heart disease.
Shunning red meats and processed food in favor of fresh fruits, vegetables, fish, nuts, olive oil, and even some wine can reduce heart attacks, strokes, and deaths from heart problems, according to the first study to demonstrate the diet's benefits using the most reliable type of clinical trial.
Rachel Johnson, head of the American Heart Association's nutrition committee, welcomed the findings. "We have moved away from the low-fat-at-all-cost message. It's important to include these healthy fats in a diet," such as olive oils and nuts.
Spanish researchers tracked thousands of participants over roughly five years and found a 30 percent reduction in the rate of heart disease, primarily strokes, among the Mediterranean diet eaters compared with people who consumed more traditional low-fat fare. That diet included more starch and grains, but fewer nuts and oils.
Earlier studies had concluded there probably were benefits from a Mediterranean diet, but they weren't definitive because of the design of the studies, including their reliance on participants' recall of meals. Health and nutrition specialists who reviewed the latest study, published online Monday by the New England Journal of Medicine, said its size, controlled structure, and focus on patients who were at risk of heart disease offered powerful and much-needed evidence of a protective heart effect from a Mediterranean diet.
Dr. Ramon Estruch, a senior consultant at the Hospital Clinic of Barcelona who led the Spanish team, said the findings should give physicians confidence to urge patients, particularly those who are overweight or have diabetes or other risk factors for heart disease, to follow a Mediterranean approach.
"As a doctor it is easier to say take a pill," Estruch said. "But diet is a very powerful effect in protecting against cardiovascular disease."
Estruch's team enrolled 7,447 people, ages 55 to 80, and then randomly assigned them to one of three groups: one that was directed to eat a Mediterranean diet that included at least 4 tablespoons a day of extra-virgin olive oil; another that also followed the Mediterranean diet and received roughly 1 additional ounce daily of a mixture of walnuts, hazelnuts, and almonds; and a third control group that was counseled to eat a low-fat diet that did not include olive oil or nuts. The olive oil included amounts used in cooking, poured on salads, and eaten in meals outside home.
All of the participants had diabetes or at least three major risk factors for heart disease, such as obesity, high blood pressure, elevated levels of bad cholesterol, or a family history of early heart disease.
Drug treatment regimens, such as medications to lower high blood pressure or cholesterol, were similar for those in all three groups.
Participants were asked annually to complete questionnaires about their health, leisure-time activities, and their diet. Scientists also tracked participants' weight, height, and waistline measurements, in addition to testing the urine and blood of those receiving the extra-virgin olive oil and nuts to confirm compliance with the diet. No restrictions were placed on how much food any of the groups could consume.
After approximately five years, scientists counted 109 heart attacks, strokes, or deaths from heart disease in the control group, which did not eat the Mediterranean diet. By comparison, there were 83 in the Mediterranean group that ate extra nuts, and 96 in the Mediterranean group that consumed additional olive oil.
Scientists said that means that for every 1,000 people who followed the Mediterranean diet, three people each year would avoid a heart attack or stroke because of the diet.
"Even the best available drugs, like statins, reduce heart disease by about 25 percent, which is in the same ballpark as the Mediterranean diet," said Dr. Walter Willett, professor of epidemiology and nutrition at the Harvard School of Public Health. "But the statins increase the risk of diabetes, whereas this diet can help reduce the risk."
This study, which focused on people at high risk for heart disease, was not designed to measure whether a Mediterranean diet also protects the hearts of healthy individuals. But Willett said that based on what scientists know about cardiovascular disease, the same diet would be beneficial in healthier people.
The Spanish researchers said their findings may have been more dramatic if they compared the Mediterranean diet with more Western fare. They said most people in Spain typically eat a version of the Mediterranean diet, so the control group's diet didn't differ much from the Mediterranean diet, likely muting the study results. "The differences probably would be huge" if the comparison group ate a typical American diet, said Dr. Miguel Angel Martinez-Gonzalez, a study co-author and chairman of the Department of Preventive Medicine at the University of Navarra.
Getting American patients to adhere to a Mediterranean diet long term can sometimes be challenging.
Jack Bishop, editorial director at America's Test Kitchen, a Brookline-based company that produces the popular TV show of the same name and Cooks Illustrated magazine, said a Mediterranean diet is easier to maintain than ones that require super low-fat intake.
"I am encouraged by this study," Bishop said. "There are so many studies that leave you aloft as to what you are supposed to do, but this one is fairly clear, and the message seems doable and satisfying at the same time.".
One unanswered question involves the type of extra-virgin olive oil used in the study. The scientists noted that they supplied a type of Spanish oil to participants that had a high level of polyphenols, a naturally occurring anti-oxidant found in fresh fruits and vegetables that is believed to have heart healthy benefits. Typical refined olive oils have much less of this substance.
Johnson, the head of the American Heart Association's nutrition committee and a nutrition professor at the University of Vermont, said the findings demonstrate that the dietary advice offered by the association and other health groups is on the right track.