by Marion Nestle
Jun 19 2018

What’s up with the retracted Mediterranean diet study?

In a most unusual action, the New England Journal of Medicine has retracted a 2013 study of Mediterranean diets and published a new version of it at the same time.

The studies asked participants to consume one of three diets: (1) a Mediterranean diet supplemented with extra-virgin olive oil, (2) a Mediterranean diet supplemented with mixed nuts, and (3) a control diet with advice to reduce dietary fat.

The authors describe Mediterranean diets as containing a

high intake of olive oil, fruit, nuts, vegetables, and cereals; a moderate intake of fish and poultry; a low intake of dairy products, red meat, processed meats, and sweets; and wine in moderation, consumed with meals.

The conclusion of the original, widely publicized, but now retracted study:

In this study involving persons at high cardiovascular risk, the incidence of major cardiovascular events was lower among those assigned to a Mediterranean diet supplemented with extra-virgin olive oil or nuts than among those assigned to a reduced-fat diet.

The conclusion of the newly analyzed version:

In this study involving persons at high cardiovascular risk, the incidence of major cardiovascular events was lower among those assigned to a Mediterranean diet supplemented with extra-virgin olive oil or nuts than among those assigned to a reduced-fat diet.

Looks the same, no?

The most thorough analysis of the study that I have seen comes from Hilda Bastian at PLoS Blogs.

Even for the full group, there was no statistically significant difference on myocardial infarction or CVD mortality – just for stroke. And in the supplementary information, there wasn’t a difference in the Kaplan Meier analysis for stroke either.

What are we to make of all this?

Diet trials are notoriously difficult to conduct and interpret and the Mediterranean diet—largely vegetarian with olive oil as the principal fat—was associated with great health and longevity based on studies of people who lived on the island of Crete immediately after the Second World War; they did not have much food to eat and were highly physically active.

And then there’s the matter of who paid for the study.  The retracted study and its revision were funded independently.  But a study published on June 13 concludes:

Adults who are overweight or moderately obese may improve multiple cardiometabolic disease risk factors by adopting a Mediterranean-style eating pattern with or without reductions in red meat intake when red meats are lean and unprocessed.

The funder?  The Beef Checkoff and the National Pork Board.

Overall, the 2015-2020 Dietary Guidelines for Americans recommends Mediterranean dietary patterns for their health benefits, defines what goes into them in Table 1.2 (p. 35), and provides more details in Appendix 4 (starting on p. 83).

Mediterranean diets are delicious.  While the scientists are arguing about exactly how healthy they might be, enjoy!

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