A 2013 study on the Mediterranean diet which found it protects against heart disease but was later withdrawn has been re-analyzed only to produce the same result.
Results that suggested the consumption of fruits, vegetables and olive oil reduced the risk of heart disease was first published in the New England Journal of Medicine, but this week an unusual “re-analysis” of the data was published in the same outlet.
The New York Times reports the data were disputed because of the way the study was conducted. Now the conclusions are the same, namely that a Mediterranean diet can cut the chances of heart attack and stroke by about 30 percent in at-risk people.
The original study was conducted in Spain by a team headed up by Dr. Miguel A. Martinez-Gonzalez of the University of Navarra. Their work enrolled 7,447 participants aged 55 to 80 who were assigned one of three diets: a Mediterranean diet with at least four tablespoons of extra virgin olive oil a day; the same diet with an ounce of mixed nuts; or a traditional low-fat diet, the New York Times reports.
The participants were followed for a median of nearly five years. The team reported that there were fewer cardiovascular events in the groups consuming olive oil and nuts.
However, the study was disputed in 2017 because the methodology seemed suspect.
A statistician at the New England Journal of Medicine suggested the researchers look at the methods at each center that recruited participants. The groups of participants were not equivalent, as some members were older or healthier than others, and so on.
But skeptics said that if subjects are not assigned at random, the investigators cannot be sure that the effects they see result from the treatment. And attempts to correct statistically after the fact are difficult.
Some of the participants were same family members, with the wife, for example, being assigned to a group and the husband in another. But that eliminates the randomized nature of the trial, because if both family members are healthy, it would be difficult to say that their diet is the only reason.
In the re-analysis, the investigators statistically adjusted data on 390 people who happened to be same family members but whose diets were not randomly assigned.
In the end of the study, researchers concluded that the original findings were still accurate.
Despite the errors presented, the doctor was reassured that the conclusions are correct with Dr. Martinez-Gonzalez believing strongly in his study on the Mediterranean diet. “After all this long work, I am more convinced than ever,” he was quoted as saying.