Effects of diet and exercise in preventing NIDDM in people with impaired glucose tolerance. The Da Qing IGT and Diabetes Study. Lifestyle changes may reverse development of the insulin resistance syndrome. The Oslo Diet and Exercise Study: a randomized trial.
Individuals with impaired glucose tolerance (IGT) have a high risk of developing NIDDM. The purpose of this study was to determine whether diet and exercise interventions in those with IGT may delay the development of NIDDM, i.e., reduce the incidence of NIDDM, and thereby reduce the overall incidence of diabetic complications, such as cardiovascular, renal, and retinal disease, and the excess mortality attributable to these complications.
                In 1986, 110,660 men and women from 33 health care clinics in the city of Da Qing, China, were screened for IGT and NIDDM. Of these individuals, 577 were classified (using World Health Organization criteria) as having IGT. Subjects were randomized by clinic into a clinical trial, either to a control group or to one of three active treatment groups: diet only, exercise only, or diet plus exercise. Follow-up evaluation examinations were conducted at 2-year intervals over a 6-year period to identify subjects who developed NIDDM. Cox's proportional hazard analysis was used to determine if the incidence of NIDDM varied by treatment assignment.
                The cumulative incidence of diabetes at 6 years was 67.7% (95% CI, 59.8-75.2) in the control group compared with 43.8% (95% CI, 35.5-52.3) in the diet group, 41.1% (95% CI, 33.4-49.4) in the exercise group, and 46.0% (95% CI, 37.3-54.7) in the diet-plus-exercise group (P < 0.05). When analyzed by clinic, each of the active intervention groups differed significantly from the control clinics (P < 0.05). The relative decrease in rate of development of diabetes in the active treatment groups was similar when subjects were stratified as lean or overweight (BMI < or > or = 25 kg/m2). In a proportional hazards analysis adjusted for differences in baseline BMI and fasting glucose, the diet, exercise, and diet-plus-exercise interventions were associated with 31% (P < 0.03), 46% (P < 0.0005), and 42% (P < 0.005) reductions in risk of developing diabetes, respectively.
                Diet and/or exercise interventions led to a significant decrease in the incidence of diabetes over a 6-year period among those with IGT. To compare and assess the single and joint effect of diet and exercise intervention for 1 year on insulin resistance and the development leading toward the insulin resistance syndrome.
                An unmasked, randomized 2 x 2 factorial intervention trial was applied with a duration of 1 year for each participant. The trial comprised 219 men and women with diastolic blood pressure of 86-99 mmHg, HDL cholesterol < 1.20 mmol/l, triglycerides > 1.4 mmol/l, total cholesterol of 5.20-7.74 mmol/l, and BMI > 24 kg/m2. Participants were randomly allocated to diet group (n = 35), diet and exercise group (n = 67), exercise group (n = 54), and control group (n = 43). The diet included increased intake of fish and reduced total fat intake. The exercise program entailed supervised endurance exercise three times a week. Baseline cross-sectional changes and 1-year changes in insulin resistance, fasting serum levels of insulin, C-peptide, proinsulin, glucose, and lipids as well as weight, mean blood pressure, and plasminogen activator inhibitor 1 (PAI-1) values were recorded.
                The cross-sectional results at baseline showed significant correlations between the calculated insulin resistance and BMI (r = 0.54) and correlations between the mean blood pressure (mBP) (r = 0.26) and PAI-1 (r = 0.40). The 1-year diet intervention gave a significant decrease in the calculated insulin resistance from 4.6 to 4.2 and a positive correlation between the changes in insulin resistance and changes in BMI (r = 0.40). The diet and exercise intervention also led to significantly decreased insulin resistance (from 5.0 to 4.0). The exercise intervention did not significantly change insulin resistance.
                The cross-sectional and 1-year intervention results supported each other and underscored the important connection between increased BMI and the development leading toward the insulin resistance syndrome.