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

Abstract

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.

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.

Keywords: Systematic review.

Fig. 1

Flow diagram showing detailed steps of the article selection process for the present meta-analysis (RR, relative risk; MD, Mediterranean diet)

Fig. 2

Forest plot showing the relative risk (RR) and 95 % confidence interval of type 2 diabetes for the highest v. lowest adherence to a Mediterranean diet score for one randomized controlled trail (RCT) and eight prospective cohort studies (122 810 subjects) published between 2007 and 2014. For each study, the black square indicates the RR, the size of which indicates the study’s weight in the analysis (weights are from random-effects analysis) and the horizontal line represents the 95 % CI. The centre of the diamond indicates the summary estimate of the RR and its width represents the 95 % CI of the summary RR estimate