Mediterranean Diet Still Best for Your Heart

Flaws in the research don’t change the results

Foods on mediterranean diet, high in healthy fats such as Salmon, olive oil, nuts and avocados with vegetables and herbs.

The best diet for a healthy heart is still the Mediterranean diet, says Steven Nissen, MD, Chair of Cardiovascular Medicine at Cleveland Clinic. The diet has received some media skepticism lately, since the 2013 research study that made it famous has been under scrutiny.

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But uncertainties about the study don’t mean uncertainties about the diet — at least for Dr. Nissen, who recommended the diet for lowering the risk of heart attack and stroke long before 2013. He referenced it in Heart 411, his 2012 book with Marc Gillinov, MD, Chair of Cleveland Clinic’s Department of Thoracic and Cardiovascular Surgery.

People on the Mediterranean diet eat:

  • Mostly fruits, vegetables, grains, olive oil and nuts.
  • Some fish and poultry — and drink some wine with meals.
  • Minimal dairy products, red meat, processed meats and sweets.

“For years we have noticed that people living in some Mediterranean countries have better heart health,” says Dr. Nissen. “We assumed it’s because of their diet. Some small research studies have supported this link, but we were thrilled when the 2013 PREDIMED trial came out. It was the best evidence yet of the Mediterranean diet’s cardiovascular benefits.”

Good evidence gone bad?

The PREDIMED trial studied more than 7,000 people in Spain who were at high risk of heart disease. Each participant was randomly assigned to one of three diets:

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  • A Mediterranean diet with more extra-virgin olive oil.
  • A Mediterranean diet with more mixed nuts.
  • A typical low-fat diet.

After following the participants for nearly five years, researchers found that those on the Mediterranean diet with olive oil or nuts were 30 percent less likely to have a heart attack or stroke than those on the low-fat diet.

That was big news. Not only was the outcome striking, it had been achieved in a “randomized controlled” study. That’s the highest standard of scientific research — difficult to conduct, yet the most reliable.

However, earlier this month we learned that the randomized study wasn’t as random as everyone thought. Some participants were assigned to a diet merely because someone they lived with had been assigned to it already. And a few test sites assigned all participants to the same diet. These technicalities could have caused biased results.

The lead researchers didn’t mention these flaws when they first published the study in The New England Journal of Medicine. So they retracted their original article — and then published another without the potentially biased data.

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Turns out the results were the same: Participants eating a Mediterranean diet still were 30 percent less likely to have a heart attack or stroke.

Old news is good news

“I give lots of credit to the journal and the authors for acknowledging the errors and republishing the study,” says Dr. Nissen. “But it really didn’t change the findings.”

Although the study is slightly weakened, evidence of the Mediterranean diet’s cardiovascular benefits is still strong, he says. He would like to see more studies confirming it. Yet he continues to recommend the diet for anyone concerned about heart health.

“In the grocery checkout line, you can see one book after another touting diets that have zero scientific evidence,” says Dr. Nissen. “The Mediterranean diet still has the best evidence of any diet.”

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