Clinical Question: For patients at high cardiovascular risk, can dietary counseling on a Mediterranean-type diet decrease the incidence of type 2 diabetes?

Bottom Line: Extensive and ongoing dietary counseling about a Mediterranean-type diet (including a high consumption of vegetables, legumes, nuts, and olive oil and a low consumption of meat and dairy products) decreased the incidence of diabetes, as compared with counseling about a low-fat diet, over 4 years in patients with 3 or more cardiovascular risk factors. The patients in this study were also supported with large quantities of free olive oil or mixed nuts. (Level of Evidence: 1b)

Reference: Salas-Salvado J, Bullo M, Babio N, et al, for the PREDIMED Study Investigators. Reduction in the incidence of type 2 diabetes with the Mediterranean diet. Results of the PREDIMED-Reus nutrition intervention randomized trial. Diabetes Care 2011;34(1):14-19.

Study Design: Randomized controlled trial (nonblinded)

Funding Source: Industry + government

Setting: Outpatient (any)

Synopsis: The Spanish researchers conducting this study enrolled 418 patients at higher risk for cardiovascular disease (defined as having at least 3 risk factors, but not diabetes). The patients were then randomized to counseling about either a low-fat diet or about 1 of 2 Mediterranean diets. All patients had quarterly individual interviews and group sessions with a dietitian, aimed at creating dietary patterns, recipes, and shopping lists; they were not counseled about calorie reduction or physical activity. Patients in the low-fat group were also counseled about fat reduction in their diet. Patients in the Mediterranean diet groups were given free allotments of olive oil (1L/week!) or mixed nuts (30 g/day). After a median follow-up of 4.0 years, diagnoses of diabetes were significantly lower in the olive oil group (10.1%) and the mixed nuts group (11.0%) than in the low-fat group (17.9%), an average 52% reduction in diabetes incidence with the Mediterranean diet counseling (95% CI, 27%-86%). Body weight and caloric expenditure were not decreased, on average, despite the decrease in diabetes incidence.