Mediterranean diet study retracted after review

In the integrative healthcare community, the Mediterranean diet has long been widely accepted for its benefits to health. Incorporating vegetables, fruits, fish, nuts, and olive oil, research has shown that people following this dietary regime show lower rates of heart disease.

The 2013 Primary Prevention of Cardiovascular Disease with a Mediterranean Diet landmark study is the first major clinical trials to measure the diet’s heart benefits. The five-year study, published in the New England Journal of Medicine, showed consuming a Mediterranean diet can lower risk of heart attack, stroke, or death from heart disease by roughly 30 percent in those at high risk.

On June 20, the study authors retracted their report, according to an editorial published on Wednesday morning. In it, the researchers explained that “due to irregularities in the randomization procedures,” they will withdraw their study and publish a new one.

The revised study offers the same conclusions as the original study, but the language has changed.  The original study said the diet “resulted in a substantial reduction in the risk” of major heart illness among high-risk people, while the new study said “those assigned” to a Mediterranean diet had a lower risk than those not assigned.

The original trial took place in Spain with over 7,000 people at high risk for heart disease assigned to one of three diets: a Mediterranean diet with extra-virgin olive oil, a Mediterranean diet with mixed nuts, and a control group on a low-fat diet.

The issue, according to the researchers, had to do with randomized controlled trials. A British anesthesiologist John Carlisle had for years been researching and reporting on cases where participants in studies were not assigned randomly to treatments, even when the study was referred to as random. His 2017 analysis looked at 5,087 randomized controlled trials over 10 years and found baseline variables that appeared near impossible to happen randomly, including 11 reports in the New England Journal of Medicine.

The journal reviewed the 11 reports and found only one of concern, the 2013 Mediterranean diet study. Carlisle’s analysis revealed questions as to whether the participants had really been assigned diets randomly. In his 2017 report, Carlisle urged the study’s authors to perform a new study.

Further review showed that individuals in the same household, and even in the same village, were assigned the same diet, making it difficult to rule out shared environmental factors that could have skewed study results.

The retraction of the 2013 study has led many in the medical community to question the legitimacy of the revised version. However, the New England Journal of Medicine stands by the results and says the evidence in favor of the diet is still strong.