Niha Zubair, Arivale Clinical Research Scientist, PhD
The Mediterranean diet – rich in fruits, vegetables, whole grains, beans, nuts and seeds, healthy oils, and fish; limited in poultry and dairy products; and very limited in red meat – has been extensively studied for its health benefits, which include well-documented benefits on heart health.
Earlier this month, however, a 2013 study in the New England Journal of Medicine titled “Primary Prevention With a Mediterranean Diet” was retracted due to questions about the validity of its methods, NPR reports. The study had concluded that people eating the Mediterranean diet supplemented with olive oil were 30 percent less likely to experience a heart attack, stroke, or death from cardiovascular causes than people assigned to a low-fat diet.
Fortunately, the paper is not being retracted completely but replaced with a “corrected” version that essentially states the individuals in the study did have reduced levels of heart attacks and strokes, but researchers can’t draw a direct causation between diet and cardiovascular outcomes.
This large randomized trial of 7,447 adults with high risk for cardiovascular disease was divided into two groups, one assigned to the Mediterranean diet (with supplemental olive oil and mixed nuts) or a control group, which followed a low-fat diet. The study participants were followed for a median of 4.8 years.
The original conclusion of the study stated that those who followed the Mediterranean diet had a reduced incidence of cardiovascular events. More specifically, those who followed a Mediterranean diet with olive oil were 30 percent less likely to experience a heart attack, stroke, or death from cardiovascular disease as compared to the group eating a low-fat diet.
Enter British anesthesiologist Dr. John Carlise, who began to evaluate the methods behind the reported outcome. Carlise looked into the randomization methods reported in the study and found discrepancies. Randomization is important in studies to avoid bias and allow researchers to determine cause and effect relationships.
When the data was audited by the study’s lead author, he found approximately 14 percent of the study’s participants hadn’t been randomly assigned. Couples that joined were put on the same diet, and in one of the 11 study sites, the lead investigator assigned the diet to an entire village and did not disclose this to the rest of the investigators.
Although this was only a small proportion of the study’s participants, as a result the study can’t claim the diet directly caused the outcomes seen.
There are thousands of published papers reporting health benefits associated with adherence to the Mediterranean diet. Although primary prevention was not able to be proven with this paper, it doesn’t remove the well-known fact that sticking to the Mediterranean diet is associated with reduced cardiovascular disease.
There are a number of systematic reviews, meta-analyses, and case-controlled studies associating the Mediterranean diet with reductions in overall mortality, cardiovascular mortality, and cancer incidence and mortality, as well as reduced incidence of Parkinson’s and Alzheimer’s disease. Studies have also found a reduced risk for colorectal, prostate, oropharyngeal, and breast cancers in those eating the Mediterranean diet.
Although this particular study was updated and its conclusions “softened,” that doesn’t change the fact that the Mediterranean diet has shown significant health benefits.
However, it’s important to note there’s no “one-size-fits-all” diet. Genetics, current health history, personal preferences, and lifestyle all play a role in determining what eating plan is appropriate for an individual. Some people are going to benefit more on a low-fat diet and others on a higher-fat Mediterranean diet. Part of the reason that studies comparing high-fat to low-fat diets – or other head-to-head diet comparisons – can never be completely perfect is precisely because people are randomized, meaning you can’t personalize the study based on their genetics, physiology, or lifestyle factors.
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[Arivale Hot Topics address health stories currently in the news. The Arivale Clinical Team’s commentary on these news articles is not a review of the scientific evidence, nor an endorsement of a specific study, and is not meant as official medical opinion.]