A Cochrane review [withdrawn from publication] examining the efficacy of a diet-only intervention for prevention of type 2 diabetes mellitus among subjects with impaired glucose tolerance included 2 studies with a total of 358 subjects. Two types of dietary advice were provided in the trials; common factors were reduction of energy intake and simple sugars, and an increase in fresh fruit and vegetables. In the 6-year Da Qing IGT & Diabetes study, the incidence of type 2 diabetes in the control group was 67.7% (95% CI 59.8% to 75.2%) which was reduced to 43.8% (95% CI 35.5% to 54.7%) in the diet group. Overall, the dietary intervention group had a 33% reduction in the incidence of diabetes after six years (P < 0.03). The Oslo Diet & Exercise Study (ODES) found significant (P<0.05) reductions in insulin resistance, fasting insulin (pmol/L), fasting C-peptide (pmol/L), fasting proinsulin (pmol/L), fasting blood glucose (mmol/L), BMI (kg/m²), mBP (mmHg) and fasting triglycerides (mmol/L), and a significant increase in fasting HDL cholesterol (mmol/L) and PAI-1 (U/ml) after 12 months of dietary intervention.
Comment: The quality of evidence is downgraded by study quality (unclear allocation concealment and inadequate intention-to-treat adherence).