Review of previous impaired glucose tolerance intervention studies

Long-term intervention studies have evaluated the effect of diet, exercise and pharmacological regimens on the conversion rate of impaired glucose tolerance (IGT) to non-insulin dependent diabetes mellitus (NIDDM). Two UK studies, the Bedford study (10 years) and the Whitehall study (5 years), found that a diet which restricts carbohydrate intake to less than 120 g/day had no effect on the development of NIDDM in subjects with IGT. In contrast, the Swedish Malmöhus study (10 years) found that the conversion rate was reduced from 29% in the control group to 13% in a group told to limit their intake of carbohydrates and lipids and to reduce weight when overweight. A further Swedish study, the Malmö study (6 years and ongoing) is investigating a combination of dietary intervention and a strenuous exercise programme. In this study the conversion rate decreased from 29% in the control group to 11% in the diet plus exercise group. The Bedford and Whitehall studies also investigated intervention with tolbutamide and phenformin, respectively. Neither drug was found to have an effect on the conversion rate in either study. In contrast, positive results for tolbutamide were obtained in the Malmöhus study. No subjects in the tolbutamide plus diet group developed NIDDM compared with 29% in the control group. This regimen was also found to have beneficial effects on blood pressure, serum lipids and on cardiovascular morbidity and mortality.