Which diet for prevention of type 2 diabetes? A meta-analysis of prospective studies.

No specific diet is recommended to prevent type 2 diabetes. We did a meta-analysis of prospective cohort studies to assess the association between different diets and prevention of type 2 diabetes. We did a comprehensive search of multiple electronic databases (Medline, Scopus, EMBASE, and ISI web of knowledge) until August 2013 using predefined criteria. We included prospective cohort studies that evaluated the role of different diets in type 2 diabetes prevention. Studies were selected by 2 independent reviewers. We did random-effects meta-analyses to determine the relative risk (RR) of incident diabetes associated with healthful dietary patterns. A total of 21,372 cases of incident diabetes, from 18 prospective studies, with 20 cohorts, in 4 world regions were identified. In the random-effect meta-analysis of the 20 cohorts, RR was 0.80 (95 % confidence interval (CI) = 0.74-0.86, P < 0.001), with high heterogeneity (I (2) = 57 %, P = 0.001) and no evidence of publication bias (Egger's test, P = 0.653). Exclusion of two cohorts produced identical RR (0.80, 95 % CI 0.76-0.84), with nonsignificant heterogeneity (I (2) = 9 %). The risk of incident diabetes did not appreciably change considering the geography (USA, Europe, and Asia), the duration of follow-up (≤10 and >10 years), and type of diets (Mediterranean and DASH, Dietary Approaches to Stop Hypertension, diets). There was a difference between at risk and general population (P = 0.0487), but the evidence was limited to two studies only. The results of our study demonstrate that several healthy diets are equally and consistently associated with a 20 % reduced risk of future type 2 diabetes.