A Mediterranean diet supplemented with olive oil or nuts reduces the risk of major cardiovascular events by 30% in comparison with a low-fat control diet. This finding from the primary prevention PREDIMED study conducted in Spain has been reported in the New England Journal of Medicine.

Trial participants were men aged 55–80 years and women aged 60–80 years who had either type 2 diabetes mellitus or at least three major risk factors for cardiovascular disease. A total of 7,447 individuals were randomly assigned to one of three diets: a Mediterranean diet with an allowance of 40 ml of extra virgin olive oil per day; a Mediterranean diet with an allowance of 30 g of mixed nuts (almonds, hazelnuts, and walnuts) per day, or a low-fat diet. No calorie restriction was specified for any of the diets.

During follow-up (median 4.8 years), the incidence of the primary end point (composite of myocardial infarction, stroke, and cardiovascular death) was lower in the Mediterranean diet groups (olive oil 3.8%; nuts 3.4%) than in the control group (4.4%). The adjusted hazard ratios for cardiovascular events for the olive oil and nut Mediterranean diets, respectively, were 0.70 (95% CI 0.54–0.92, P = 0.01) and 0.72 (95% CI 0.54–0.96, P = 0.03) compared with control.

The investigators caution that their results need to be confirmed in other populations, because the trial was conducted in a Mediterranean country in which the normal diet of most trial participants closely mirrored the two study diets. However, they hypothesize that their findings “might explain, in part, the lower cardiovascular mortality in Mediterranean countries than in northern European countries or the USA”.