Mediterranean diet shown to reduce heart disease, landmark study finds

By Kay Lazar, Globe Staff

Consumers have, for years, been urged to eat a Mediterranean diet, which eschews red meats and processed food in favor of fresh fruits, vegetables, fish, nuts, olive oil, and wine, but the advice lacked a rigorous study to prove it prevented heart disease. Now there is one.

A Mediterranean diet supplemented with extra-virgin olive oil or mixed nuts can significantly reduce heart attacks, strokes, and deaths from heart problems, according to a study that is the first to demonstrate its benefits in a type of clinical trial considered the most reliable.

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 those who consumed more traditional low-fat fare. That diet included more starch and grains, but fewer nuts and oils.

Earlier studies analyzed health outcomes based on participants’ recall of meals and concluded there likely were benefits from a Mediterranean diet. 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 already 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, age 55 to 80, and then randomly assigned them to one of three groups: one that ate 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 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 the home.

All of the study 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 just 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.”

Willett said other studies have suggested another benefit of a Mediterranean diet, in reducing the risk of some forms of cancer, such as estrogen negative breast cancer. The new study didn’t examine this aspect.

Getting patients to adhere to a Mediterranean diet long term can sometimes be challenging, and Willett suggested that patients consider adding as many components of the diet as possible to their own, perhaps incorporating different spices to add variety.

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.

“How much that extra-virgin olive oil contributed to the heart benefit remains a question not completely answered,” Willett said.

Rachel Johnson, a registered dietician who heads the American Heart Association’s nutrition committee, said the findings demonstrate that the dietary advice offered by the association and other health groups is on the right track.

“It’s nice to see science validated and reaffirmed with such a strong study design,” said Johnson, Bickford professor of nutrition at the University of Vermont. “We have moved away from the low fat at all cost message. It’s important to include these healthy fats in a diet.”

Johnson said she would like to see a follow-up study that included a Mediterranean diet and efforts to control weight with increased exercise to determine if that added component would further reduce heart disease risks.

Estruch, the study’s lead author, said his team is planning such a follow-up.