The Mediterranean Diet: A Closer Look (The PREDIMED Study)
Updated: May 12, 2019
Q: There have been many news reports on a recent study in the NEJM on the Mediterranean diet. The reports all said it was a well designed study without any major flaws. The results showed that olive oil and nuts were more protective than a low-fat diet in regard to cardiovascular disease. Is this true?
A. The study in question was recently featured in the NY Times Health section in the article, Mediterranean Diet Shown to Ward Off Heart Attack and
The NY Times article stated, "About 30 percent of heart attacks, strokes and deaths from heart disease can be prevented in people at high risk if they switch to a Mediterranean diet rich in olive oil, nuts, beans, fish, fruits and vegetables, and even drink wine with meals, a large and rigorous new study has found."
They were reporting on a study that was published in the New England Journal of Medicine where that randomly assigned 7,447 people in Spain who were overweight, were smokers, or had diabetes or other risk factors for heart disease to follow a Mediterranean diet with added olive oil, a Mediterranean diet with added nuts, or a low-fat diet.
Since this study is getting so much attention, let's take a closer look at the study.
To me, this is a great example of a study that is being misrepresented by both the researchers & the media. The flaws in the way it is being reported are enormous and only further my concerns about how media misrepresents health info & how researchers can promote conclusions that are not supported by their work.
Here are some of the problems with the study;
- The low fat group was not low fat at all as they consumed a diet that was 37% fat.
- In addition, the reduction in fat they experienced over the course of the study was only from 39% to 37% fat, a 2% reduction. Not only was the group not low fat, they experienced a non-significant reduction in total fat.
- The authors knew from the very beginning that the group they were calling low fat would have poor compliance and they actually stated that in an earlier paper on the same study and diet
"Limitations of the study: Fat consumption is customarily high in Mediterranean countries. Due to this fact, some participants have difficulty in following a low-fat diet on the long-term. We acknowledge this limitation because participants in the low-fat diet Control group belong to a Mediterranean culture and their food habits are derived from the fat-rich traditional MeDiet (Serra-Majem, 2007)."
- In spite of knowing this and the difficulty the low fat group would have in complying, the low fat group received virtually no support at all in following this diet during the first half of the study.
- The low fat group was also encouraged to consume refined grains & carbs and even sugary drinks (like sodas).
- The low fat group still consumed fatty dairy & meat.
- As reported on the 1, 3, and 5-yr follow-up diet scores, the 2 experimental groups (the olive oil and nut groups) consumed a statistically significant greater amount of legumes, vegetables and fruits and less butter, cream and margarine than the control group (the low-fat group). The experimental groups also consumed less commercial bakery products on the 1 and 3-yr follow ups than the control group.
- While I do not think funding itself is always an issue, this study was not well done, is being misrepresented & the funding sources of the lead authors sounds like the marketing team for the Mediterranean travel & tourism bureau (See below).
- The two Mediterranean diet groups were encouraged to include sources of omega 3 fatty acids which may be heart healthy. On the other hand, the low fat diet groups was discouraged from consuming sources of omega 3's. This may turn out to be the real difference that mattered in this study, as neither olive oil nor nuts (which are being promoted as being the dietary factor that made the difference that mattered) are a significant source of Omega 3's
- There was no significant difference for most all outcomes including heart attacks (myocardial infarction), death from cardiovascular causes, or death from any cause. The only significant difference was for stroke, which is not surprising considering the emphasis on omega 3’s in the 2 experimental groups.
- The absolute differences between the groups was not great and it could be viewed that all groups experienced somewhat similar rates of disease. So another way to look at it is that all 3 high fat Mediterranean diets produced similar rates of disease but the groups that emphasized healthier foods and more omega 3's, experienced a little less disease. They were also more at risk for stroke from the beginning.
- The conclusion of the study should be that they found a significant reduction in stroke in those consuming a Mediterranean diet encouraged to be higher in omega‑3 fatty acids and healthier foods when compared to those who were not making these same changes in their diet.
That is not new news and should have been expected and does not in anyway compare to the results we see with our programs.
N Engl J Med 2013; 368:1279-1290 DOI: 10.1056/NEJMoa1200303
Lead Authors and Funding Sources
Dr. Estruch reports serving on the board of and receiving lecture fees from the Research Foundation on Wine and Nutrition (FIVIN); serving on the boards of the Beer and Health Foundation and the European Foundation for Alcohol Research (ERAB); receiving lecture fees from Cerveceros de España and Sanofi-Aventis; and receiving grant support through his institution from Novartis.
Dr. Ros reports serving on the board of and receiving travel support, as well as grant support through his institution, from the California Walnut Commission; serving on the board of the Flora Foundation (Unilever); serving on the board of and receiving lecture fees from Roche; serving on the board of and receiving grant support through his institution from Amgen; receiving consulting fees from Damm and Abbott Laboratories; receiving consulting fees and lecture fees, as well as grant support through his institution, from Merck; receiving lecture fees from Danone, Pace, AstraZeneca, and Rottapharm; receiving lecture fees and payment for the development o