Retracted, Redone Mediterranean Diet Study Shows Same Result: Good

Greek salad. (Photo by Eurokinissi, file)

It’s unlikely to surprise people in Greece and on the island of Crete where they’ve been eating fruits, vegetables, nuts and olive oil since ancient times, but a study redone after its methods were found to be flawed has come to the same conclusion: the Mediterranean Diet works.

It took the authors to swallow their pride and acknowledge errors in how the study published in the New England Journal of Medicine in 2013 was done but one of the lead researchers,  Dr. Miguel A. Martínez-González of the University of Navarra in Spain, said the result was gratifying.

“After all this long work, I am more convinced than ever” by the study’s data that was redone after some embarrassing moments when the original work was questioned. “Seldom has a trial undergone more scrutiny,” he added.

The results of the retracted, redone study were reported in the New York Times and showed that despite some skepticism that the Mediterranean Diet can cut risk of heart attacks and strokes by 30 percent in those at high risk.

While the research was done in Spain, the diet studied was strikingly similar to that in Greece and other Mediterranean countries and the re-analysis showed essentially what the landmark original did.

Not everyone is convinced. “Nothing they have done in this re-analyzed paper makes me more confident,” said Dr. Barnett Kramer, Director of the Division of Cancer Prevention at the National Cancer Institute told the paper.

The flaws threatened to undercut the credibility of the study, especially among doubters and because the assignment of diets into three groups wasn’t as random as it was supposed to be, skewing the first results.

The trial enrolled 7,447 participants aged 55 to 80 who were assigned one of three diets: a Mediterranean diet with at least four tablespoons a day of extra virgin olive oil; the same diet with an ounce of mixed nuts; or a traditional low-fat diet.

The participants were followed for a median of nearly five years. Dr. Martínez-González and his colleagues reported that there were fewer cardiovascular events in the groups consuming olive oil and nuts.

All that came into question last year when Dr. John Carlisle of Torbay Hospital in England challenged the data and a statistician at the New England Journal of Medicine suggested the researchers look at the methods at each center that recruited participants and the not-so-random assignments in some cases.

On re-evaluating their data, the scientists running the new study soon found what Dr. Martínez-González said were “small problems affecting 10 percent of participants.”

Some investigators would assign one person in a household — the wife, for example — to one arm of the study — say, to the group consuming olive oil. Then they would ask other members of the household to share that diet, including them as though they had been randomly assigned to it.

We realized we had never reported that,” Dr. Martínez-González said.It got worse.

A researcher at one of the 11 clinical centers in the trial worked in small villages. Participants there complained that some neighbors were receiving free olive oil, while they got only nuts or inexpensive gifts.

So the investigator decided to give everyone in each village the same diet. He never told the leaders of the study what he had done. “He did not think it was important,” Dr. Martínez-González said.

It was because it meant the participants were not randomized and forced the team make another adjustment to data on 652 people in the trial along with 390 others who hadn’t been randomly assigned one of the three diets.

The investigators spent a year working on the re-analysis in collaboration with Dr. Miguel Hernan of the Harvard T.H. Chan School of Public Health.

In the end, they concluded that the original findings were still accurate, but the disbelievers remain unconvinced and excoriated the researchers and the work that created a flawed study in the first place.

“These people were naïve,” said Donald Berry, a statistician at MD Anderson Cancer Center in Houston.  “They were sloppy and didn’t know they were being sloppy.”

He said he wants to believe because he loves nuts and has taken to cooking with extra virgin olive oil but doesn’t think the re-analysis solved the study’s problems beyond a doubt that can’t be calculated.

But he remains unconvinced, because the re-analysis did not solve the study’s problems, he said.

Dr. Bradley Efron, a statistics professor at Stanford University, also was skeptical. The revamped results “wouldn’t convince me to be on a Mediterranean diet,” he said.

Dr. Steven Nissen, a cardiologist at the Cleveland Clinic, is persuaded though and said he plans to continue advising patients to go on the Mediterranean Diet and is satisfied with the new findings that were the old findings.

It turned out about 14 percent of the more than 7,400 study participants hadn’t been assigned randomly to either the Mediterranean Diet or a low-fat one.

“This affected only a small part of the trial,” said Martínez González. When the researchers reanalyzed the data excluding the nonrandomized people, the results were the same, he added

Still, because everybody wasn’t randomly assigned to different groups, the study can no longer claim the diet directly caused those health benefits. “We need to tone down the results, but it is just a little bit,” he said, according to NPR.

David Allison, Dean of the School of Public Health at Indiana University in Bloomington told the radio station some logic is needed too, the way he put it.

“I don’t know anybody who would turn around from this and say, ‘Now that this has been revealed, we should all eat cotton candy and turn away from the Mediterranean Diet,'”