Major Mediterranean Diet Study Is Flawed: What Was Wrong With The Landmark Research?


The New England Journal of Medicine on Wednesday retracted and republished a landmark study originally published in April 2013.

The research said that Mediterranean diet can significantly slash the risk of heart disease in people with high cardiovascular risk.

The authors of the Spanish government-funded study wrote in a letter published on NEJM on June 13 that there were irregularities in the randomization procedures of the study, and they have revised their report.

Studies With Questionable Data

The retraction came after John Carlisle of Torbay Hospital in England had scrutinized thousands of studies published from 2000 to 2015 and flagged the Mediterranean diet study as one of the medical reports with questionable data.

NEJM contacted the authors of the 11 studies flagged as suspicious. Within a week, 10 of the cases were resolved. Carlisle was wrong in five, while the authors of the five other studies committed terminology errors.

Problem With The Landmark Mediterranean Diet Study

The last study was the one that established consuming lots of fish, olive oil, vegetable, and nuts can reduce heart risk. After digging through the records, the researchers discovered that one study site did not strictly follow the procedures.

Miguel ángel Martínez-González, the lead author of the study, said that 14 percent of the nearly 7,450 participants had not been randomly assigned.

A field researcher decided to assign an entire village to a single group because some of the participants complained that their neighbors receive free olive oil, which means that the group assigned was not truly random.

Nonetheless, after reanalyzing the results without this group, the findings remained the same: Mediterranean diet can reduce the risk of heart attacks and strokes by about 30 percent among people who have high chances of developing cardiovascular disease.

"We have withdrawn our previously published report and now report revised effect estimates based on analyses that do not rely exclusively on the assumption that all the participants were randomly assigned," Martínez-González and colleagues wrote.

Retracted And Republished

The journal published the two versions of the study. Jeffrey Drazen, NEJM editor-in-chief, said that medical professionals and their patients can now use the information from the published version of the study with confidence.

"When we discover a problem we work very hard to get to the bottom of it," Drazen said. "There's no fraud here as far as we can tell. But we needed to correct the record."

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