Adherence to a Mediterranean diet and risk of diabetes: a systematic review and meta-analysis

Objective: Adherence to a Mediterranean diet is associated with significant improvements in health status. However, to date no systematic review and meta-analysis has summarized the effects of Mediterranean diet adherence on the risk of type 2 diabetes mellitus. Design: Electronic searches for randomized controlled trials and cohort studies were performed in MEDLINE, SCOPUS, EMBASE and the Cochrane Trial Register until 2 April 2014. Pooled effects were calculated by an inverse-variance random-effect meta-analysis using the statistical software Review Manager 5.2 by the Cochrane Collaboration. Setting: Meta-analysis of randomized controlled trials and cohort studies. Subjects: Eligibility criteria: 19+ years of age. Results: One randomized controlled trial and eight prospective cohort studies (122 810 subjects) published between 2007 and 2014 were included for meta-analysis. For highest v. lowest adherence to the Mediterranean diet score, the pooled risk ratio was 0.81 (95 % CI 0.73, 0.90, P < 0.0001, I-2 = 55 %). Sensitivity analysis including only long-term studies confirmed the results of the primary analysis (pooled risk ratio = 0.75; 95 % CI 0.68, 0.83, P < 0.00001, I-2 = 0 %). The Egger regression test provided no evidence of substantial publication bias (P = 0.254). Conclusions: Greater adherence to a Mediterranean diet is associated with a significant reduction in the risk of diabetes (19 %; moderate quality evidence). These results seem to be clinically relevant for public health, in particular for encouraging a Mediterranean-like dietary pattern for primary prevention of type 2 diabetes mellitus.