Back in 2013, a study on the effect of the Mediterranean diet on people at high risk of heart disease and strokes shook the medical community. The study had concluded that a regime based on the Med diet could help reduce those incidents by 30 percent.
No previous trial has undergone such intense scrutiny.
But last week, the study was retracted to be reviewed by its authors, and then it was again released with the same results but a different tone in the language used.
The study, published in the New England Journal of Medicine, was huge both in terms of the time it took and the people involved; It went on for five years monitoring more than 7,000 people in 11 areas of Spain, who were following a specific diet assigned to them. Smokers, overweight, and diabetics were found to undergo fewer cardiovascular events if they switched to a Mediterranean eating style with four tablespoons of extra virgin olive oil a day, or the same diet but with an ounce of nuts a day.
Until the study was performed, evidence that the Mediterranean diet could help people suffering from heart disease was mostly based on observations that those living in countries of the Mediterranean basin had lower rates of incidents. Scientists already suspected that their eating habits were behind it, but there was room for other factors too, like environmental conditions or their specific lifestyle.
The initial report had gained a lot of praise because clinical trials in the field are difficult to carry through, due to the fact that participants have to stick to a certain behavioral pattern and must be monitored continuously.
But it was the statistical analysis of one physician, John Carlisle, which showed that some of the data used in the study were not properly collected. The actual problem was that the study presupposed that diets were randomly assigned to the participants to ensure that a possible improvement in their health condition stemmed from the diet and only that, but this was not always true.
In a few cases, the same diet was assigned to a whole family or even a whole village, possibly causing faulty results since data was collected from a group of people sharing many common habits and environmental parameters. The investigators could not be certain whether the diet or other common factors had led to their improved conditions.
The re-evaluation of the findings of the original research took almost one year to complete. In their revised report, the researchers made statistical adjustments to compensate for the matters raised. They also changed the vocabulary and expressions used.
It is quite common for scientific papers to go under the microscope of academics after publication who look for discrepancies and possible rogue data, but it is highly uncommon for authors to retract and review their work.
Miguel A. Martínez-González, one of the researchers, told The Washington Post that after reviewing their initial work, he and the rest of the team were more confident of their conclusions since they were actually double-checked and reaffirmed. The team “took more care to adjust for potential imbalances,“ he added. “No previous trial has undergone such intense scrutiny.”
But the event caused mixed reactions from other researchers. Donald Berry, a statistician at MD Anderson Cancer Center in Houston, told the New York Times that the investigators “were sloppy and didn’t know they were being sloppy.” He added that, while he uses olive oil for cooking, he is still not sure about the specific study.
Bradley Efron, a professor at Stanford, said that the reviewed study was not enough to make him stick to a Mediterranean diet.
Cardiologist Steven Nissen of the Cleveland Clinic said he was thrilled to see “an impeccable trial” in the first paper, and the reviewing of it “reassured” him that the results were correct.
The Mediterranean diet is perhaps the most celebrated dietary regime on the planet, with hundreds of reports and studies showing its beneficial effects. The study in question was reviewed and re-published with the outcome being the same, that a Med diet eating pattern can help people at high risk suffer 30 percent less from heart attacks and strokes.
But regardless of the study’s outcome, as John Carlisle said, “Whatever you believe, it shouldn’t depend upon just one paper. Try to have not only a balanced diet but also a balanced view.”