A Cochrane review included 8 studies with a total of 5956 subjects. All 8 studies had an exercise plus diet and a standard recommendation group and 2 studies also had a exercise only group. Study duration ranged from one to six years. Interventions varied between studies but mainly consisted of caloric restriction if the person was overweight, low fat content (especially saturated fat), high carbohydrate content and the increase of fibre intake. Physical activity varied but on average at least 150 minutes each week of brisk walking or other activities such as cycling or jogging were recommended.
Overall, exercise plus diet interventions reduced the risk of diabetes compared with standard recommendations (RR 0.63, 95% CI 0.49 to 0.79; 8 studies, n=4228) and had favourable effects on body weight, waist circumference and blood pressure. No statistically significant effects on diabetes incidence were observed (RR 0.69, 95% CI 0.37 to 1.29; 2 studies, n=351) when comparing exercise only interventions with standard recommendations, although the larger trial alone showed a positive effect of exercise in preventing diabetes. No firm conclusion can be drawn about the effectiveness of exercise alone in preventing diabetes.