We conducted a systematic review of the available studies that assessed the effect of a Mediterranean diet in type 2 diabetes. We searched publications up to 30 November 2009. Seventeen studies were included. Two large prospective studies report a substantially lower risk (83% and 35%, respectively) of type 2 diabetes in healthy people or in post-infarct patients with the highest adherence to a Mediterranean diet. Five randomized controlled trials have evaluated the effects of a Mediterranean diet, as compared with other commonly used diets, on indices of glycaemic control in subjects with type 2 diabetes. Improvement of fasting glucose and HbA1c levels was greater with a Mediterranean diet and ranged from 7 to 40mg/dl for fasting glucose, and from 0.1 to 0.6% for HbA1c. No trial reported worsening of glycaemic control with a Mediterranean diet. Two controlled trials in a secondary prevention setting demonstrated that post-infarct patients, including diabetic patients, had cardiovascular benefits from a Mediterranean diet. The evidence so far accumulated suggests that adopting a Mediterranean diet may help prevent type 2 diabetes, and also improve glycaemic control and cardiovascular risk in persons with established diabetes.
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