Mediterranean diets reduced cardiovascular events more than a low-fat diet in high-risk persons

A randomized controlled trial (RCT) in Spain included older patients with type 2 diabetes mellitus or at least three major risk factors for cardiovascular disease. They were assigned to one of three diets: a Mediterranean diet supplemented with extra-virgin olive oil, a Mediterranean diet supplemented with mixed nuts, or a control diet (advice to reduce dietary fat). The trial was stopped after a median follow-up of 4.8 years, when the two Mediterranean diet groups had significantly lower rates of cardiovascular events.

The study was published in the April 4 New England Journal of Medicine. The following commentary by Paul Glasziou, RACGP, PhD, was published in the ACP Journal Club section of the June 18 Annals of Internal Medicine.

Interest in the possible benefits of a Mediterranean diet was boosted in 1994 when a large French trial found that it reduced mortality in patients after myocardial infarction. The large RCT by Estruch and colleagues provides replication and has the power to examine effects on CV events. The results echo the earlier French study and extend the findings to persons at high risk for CV disease. If we accept that the diet is effective, clinicians and patients will have questions, including: What is a Mediterranean diet? How does it work? What are the important components?

The small improvements in weight, blood pressure, glucose, and C-reactive protein shown in a meta-analysis of the effects of the Mediterranean diet on risk factors are not enough to explain the results. Perhaps it was antiarrhythmic effects of omega-3 fatty acids, but a meta-analysis of omega-3 supplements was disappointing and could not explain the effects. One simplification is that there was no difference between the olive oil– and nut-enhanced diets, so we would be free to choose either. But without knowing what the other effective elements were, we will need to use the whole intervention package, which included individual assessment and tailoring by a nutritionist, with both individual and group sessions. The appendices and Web site of the PREDIMED trial provide many needed details but are largely in Spanish. Considerable enthusiasm and work by clinicians will be needed to implement the intervention! It is certainly more than a handful of free mixed nuts but might be worth the (tasty) effort.