Does a combined program of dietary modification and physical activity or the use of metformin reduce the conversion from impaired glucose tolerance to type 2 diabetes?

« Design: A cluster-randomised controlled trial with four arms.Setting: 33 health clinics in Da Cling, China.Patients: 557 people (mean age, 46.5 years; mean body mass index [BMI], 25.8 kg/m(2); 46.6% female) of more than 110 000 screened for diabetes who were found to have impaired glucose tolerance (IGT) on the basis of a two-hour glucose tolerance test (GTT) and who agreed to participate.Interventions: The arms were control, diet only, physical activity only, and diet plus physical activity. For people who were not overweight (BMI 25 kg/m(2)) who were overweight were encouraged to lose weight gradually but details of the diet were not specified. Patients received individual counselling and also attended group sessions. The exercise intervention was to increase physical activity by one unit, and preferably two units, per day (eg, 1 unit was 30 minutes of slow walking or five minutes of swimming). The control group was given general information about diabetes and IGT and a pamphlet about diet and exercise.Main outcome measure. Diabetes (glucose level > 11.1 mmol/L), determined by biennial two-hour GTT and confirmed by a repeat GTT. Patients also had three-monthly urine tests; if results were positive, plasma glucose was tested after a standard breakfast (100 g steamed bread). If plasma glucose was > 11.1 mmol/dL, or if the doctor suspected diabetes, a 75 g GTT was performed. Subjects also received a GTT if they had signs of diabetes at any time.Main results: Compared with the control group (six-year incidence, 15.7/100 person-years [py]) the incidence of diabetes was significantly reduced in all three intervention groups: 10.0/100 py in the diet group, 8.3/100 py in the exercise group and 9.6/100 py in the combined group. The interventions also reduced the incidence of diabetes within subgroups of those who were overweight and not overweight at baseline. Among those who were not overweight, all groups gained a small amount of weight, whereas among those overweight at baseline all groups lost weight, with the control and exercise groups both losing an average of 0.9 kg/m(2). There was no significant difference in the proportion of dietary energy derived from fat between the groups at follow-up. The two exercise groups significantly increased their exercise by 0.6 units/day (exercise only) and 0.8 units/day (exercise and diet), compared with 0.1 units/day in the control group.Conclusion: The authors concluded that increasing physical activity or altering the diet reduced the incidence of conversion from impaired glucose tolerance to diabetes. Combining physical activity with dietary modification was not more efficacious than altering one component alone. «