February 25th, 2013
Large Trial Shows Cardiovascular Benefits of Mediterranean Diet
A large new trial offers powerful evidence that a Mediterranean diet can reduce the risk for cardiovascular disease. Results of the PREDIMED (Prevención con Dieta Mediterránea) study were published online in the New England Journal of Medicine.
Investigators in Spain randomized 7447 people at high risk for cardiovascular disease to one of three diets: a Mediterranean diet supplemented with extra-virgin olive oil, a Mediterranean diet supplemented with nuts, or a control diet for which people were advised to lower their intake of dietary fat. The diets were designed not to restrict calories but to change the composition of the diet.
The trial was stopped early in July 2011 by the data and safety monitoring board when the benefits in the Mediterranean diet groups crossed a predetermined boundary. After 4.8 years of follow-up a primary endpoint event (the composite of MI, stroke, and death from CV causes) occurred in 3.8% of patients in the Mediterranean diet extra-virgin olive oil group, 3.4% in the Mediterranean diet with nuts group, and 4.4% of patients in the control group. After adjusting for small differences among the groups, the hazard ratios for the two Mediterranean diet groups were 0.70 (95% CI, 0.54-0.92) and 0.72 (95% CI, 0.54-0.96). The benefit in favor of the Mediterranean diet groups occurred early in the trial and continued throughout the follow-up period. The results were consistent across a broad range of subgroups.
Given that the results appear consistent with those from previous smaller trials and observational studies, the authors said that “a causal role of the Mediterranean diet in cardiovascular prevention has high biologic plausibility. The results of our trial might explain, in part, the lower cardiovascular mortality in Mediterranean countries than in northern European countries of the United States.”
The authors said the benefits of the Mediterranean diet may be explained by several different factors, including moderate alcohol consumption, low consumption of meat, and high consumption of vegetables, fruits, nuts, legumes, fish, and olive oil.
“Perhaps there is a synergy among the nutrient-rich foods included in the Mediterranean diet that fosters favorable changes in intermediate pathways of cardiometabolic risk, such as blood lipids, insulin sensitivity, resistance to oxidation, inflammation, and vasoreactivity.”
One limitation, acknowledged by the authors, is that the reduction in total fat intake in the control group was small. In addition, although people in the Mediterranean diet groups ate more fish and legumes, they did not substantially alter other aspects of their diet. The authors speculated that the consumption of the recommended olive oil and nuts, which were distributed for free to patients in the Mediterranean diet groups, may have been “responsible for most of the observed benefits of the Mediterranean diets.”
One PREDIMED investigator, Emilio Ros, told CardioExchange that he believes the results of the trial mean that current recommendations regarding dietary fat should be changed to reflect that a “high fat, high vegetable fat diet is optimal for cardiovascular health.” Another study investigator, Ramón Estruch, said that “a major problem with low-fat diets is their low potential for long-term sustainability.” He said that the results clearly demonstrate “the superiority of the Mediterranean diets.”