The Mediterranean Diet: What Are the Benefits?

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The Mediterranean diet may help prevent diabetes, cardiovascular disease, and cancer.
The Mediterranean diet may help prevent diabetes, cardiovascular disease, and cancer.

Randomized controlled trials provided some limited evidence that a Mediterranean diet without fat restriction may reduce the incidence of cardiovascular disease (CVD), cancer, and diabetes, according to a new systematic review. However, there was no observed effect on all-cause mortality.1

The Mediterranean diet first appeared in the medical literature in 1970 with the publication of the initial results of the Seven Countries Study by biologist Ancel Keys, PhD.  Dr Keys' report suggested that there was a lower incidence of CVD and coronary artery disease (CAD) in populations near the shores of the Mediterranean Sea. The diet was described as high in fruits, vegetables, whole grains, and fat primarily from nuts and olive oil, and low in meat.2 

Studies that have investigated the Mediterranean diet have also included fatty fish with ω-3 polyunsaturated fatty acids and lower-fat dairy products.2

In contrast, the standard Western diet tends to be higher in refined grains, saturated fats, and sugar. Diabetes, cancer, and CVD are major causes of mortality and morbidity in the United States with a suspected causal link to the suboptimal Western diet.1

Hanna E. Bloomfield, MD, MPH, of the Center for Chronic Disease Outcomes Research, the Minneapolis VA Health Care System, and professor of medicine at the University of Minnesota in Minneapolis, and colleagues conducted a systematic review and meta-analysis of studies assessing the outcomes of the Mediterranean diet with unrestricted fat content. Studies included in the review investigated the impact of the Mediterranean diet on primary prevention, progression, and mortality related to diabetes, CVD, hypertension, cancer, rheumatoid arthritis, kidney disease, and cognitive impairment. 

Of 10,349 abstracts, only 56 studies met their inclusion criteria. Of those included, 44 assessed primary prevention, 12 assessed secondary prevention, and no studies addressed adherence.

The analysis included 2 randomized control trials on primary prevention, which demonstrated no difference in all-cause mortality. The PREDIMED study had 7447 participants and compared the Mediterranean diet with olive oil, the Mediterranean diet with nuts, and a low-fat diet. Results indicated a lower incidence of diabetes (hazard ratio [HR], 0.70; 95% CI, 0.54-0.92), breast cancer (HR, 0.43; 95% CI, 0.21-0.88), and major CV events (HR, 0.71; 95% CI, 0.56-0.90) with the combined data from the 2 Mediterranean diets.1

Pooled analysis of 28 cohort studies with more than 2 million participants suggested that participants in the highest quantile of Mediterranean diet adherence had a 14% lower cancer mortality (risk ratio [RR], 0.86; 95% CI, 0.82-0.91) and a 4% decrease in cancer incidence (RR, 0.96; 95% CI, 0.95-0.97).1 Likewise, there was a 9% reduction in colorectal cancer incidence in the pooled data (RR, 0.91; 95% CI, 0.84-0.98) and a lower risk for breast cancer (RR, 0.96; 95% CI, 0.90-1.03) for the highest quantile of adherence.1 

For secondary prevention, only 1 of 3 randomized control trials showed a reduction in recurrent myocardial infarction risk (RR, 0.32; 95% CI, 0.15-0.70) and CV death risk (RR, 0.32, 95% CI: 0.13-0.78) with a Mediterranean diet.1

Cohort studies found similar cancer-related mortality and cancer recurrence between the lowest and highest quantile of adherence to the Mediterranean diet.1

Proposed mechanisms of the positive clinical outcomes include decreases in inflammatory markers, glucose, LDL cholesterol, and body weight associated with a Mediterranean diet.1

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