June 13, 2018

expert reaction to retraction and republication of study looking at Mediterranean diet and heart disease

The article “primary prevention of cardiovascular disease with a mediterranean diet” has been retracted from the NEJM.

Dr Ian Johnson, Nutrition researcher and Emeritus Fellow, Quadram Institute Bioscience, said:

“The original paper was a rare example of an intervention trial with the whole diet as a variable and disease as the endpoint.  The paper is quite important in the diet field so a full scale retraction would have been significant – however my reading of this is that some initial statistical discrepancies have now been properly accounted for and that nothing has changed so far as the conclusions of the research are concerned.”

Prof Tom Sanders, Professor emeritus of Nutrition and Dietetics, King’s College London, said:

“It looks like there may have been some inconsistencies in the randomisation in the original paper.  However, the overall conclusion from the reanalysis does not change the overall conclusion that following a Mediterranean type diet has health benefits in terms of reducing risk of cardiovascular disease, which was the primary endpoint.

“Excluding site D, the results suggest that for every 1000 subjects enrolled over a five year period there would be 25 fewer cases of cardiovascular disease in the group who received the virgin olive oil group compared to the control group.  The difference was in the same direction for the virgin olive oil plus nuts but did not achieve statistical significance.  For the combined olive oil plus olive oil and nut groups compared to control there were 23 fewer cases of cardiovascular disease.  It is notable that on the secondary endpoints the reduction in risk of death from stroke was significant.  Stroke is strongly linked to raised blood pressure rather than elevated blood cholesterol.  There did not appear to be a significant effect on heart attacks (myocardial infarction).

“These main conclusions are the same as in the originally published study.”

Prof Naveed Sattar, Professor of Metabolic Medicine, University of Glasgow, said:

“This is a highly unusual step and I am sure that the NEJM took this decision very seriously and did a thorough investigation and asked the authors to rea-analyse in a manner that would satisfy their statistical reviewers.  It is reassuring to see results remain broadly similar but that said, for some people, this retraction and re-analysis might somewhat influence their view of the robustness of the trial results.  On the other hand, as the new paper is now also in NEJM, we have to accept that due process was done and that results remain valid and so it is unlikely recent guidelines which included these findings on Mediterranean diets will be revised.  Overall, this whole process will, I believe, lead to future lifestyle and diet trials to be of higher standards.”

* ‘Primary prevention of cardiovascular disease with a Mediterranean diet supplemented with extra-virgin olive oil or nuts’ by R. Estruch et al. published in the NEJM on Wednesday 13 June 2018.

Declared interests

Dr Ian Johnson: “No conflicts of interest.”

Prof Tom Sanders: “Honorary Nutritional Director of HEART UK.  Scientific Governor of the British Nutrition Foundation.”

Prof Naveed Sattar: “No COI.”