AbstractObjectiveAdherence 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.DesignElectronic 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.SettingMeta-analysis of randomized controlled trials and cohort studies.SubjectsEligibility criteria: 19+years of age.ResultsOne 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, I²=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, I²=0 %). The Egger regression test provided no evidence of substantial publication bias (P=0·254).ConclusionsGreater 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.