Scientific Study

Objective: To test the effects of two Mediterranean-diet interventions versus a low-fat diet on incidence of diabetes. Research Design and Methods: Three-arm randomized trial in 418 nondiabetic subjects aged 55-80 years recruited in one center (PREDIMED-Reus; North-Eastern Spain) of the PREDIMED study; a large nutrition-intervention trial for primary cardiovascular prevention in persons at high cardiovascular risk. Participants were randomized to education on a low-fat diet (control group) or one of two Mediterranean diets; supplemented with either free virgin olive oil (1 liter/week) or nuts (30 g/day). Diets were ad libitum and no advice on physical activity was given. The main outcome was diabetes incidence diagnosed by the 2009 American Diabetes Association criteria. Results: After a median follow-up of 4.0 years; diabetes incidence was 10.1% (95% confidence interval [CI]; 5.1-15.1); 11.0% (5.9-16.1); and 17.9% (11.4-24.4) in the Mediterranean-diet with olive oil group; the Mediterranean-diet with nuts group; and the control group; respectively. Multivariable-adjusted hazard ratios of diabetes were 0.49 (0.25-0.97) and 0.48 (0.24-0.96) in the Mediterranean-diet groups supplemented with olive oil and nuts; respectively; compared to the control group. When pooling the two Mediterranean-diet groups compared to the control group; diabetes incidence was reduced by 52% (27-86). In all study arms; increased adherence to the Mediterranean-diet was inversely associated with diabetes incidence. Diabetes risk reduction occurred in the absence of significant changes in body weight or physical activity. Conclusion - Mediterranean diets without calorie restriction appear to be effective in the prevention of diabetes in subjects at high cardiovascular risk.