BACKGROUND: In short-term studies, diet and exercise both improve insulin sensitivity. OBJECTIVE: To determine the effects of a 48-week supervised diet and exercise program on weight and insulin sensitivity after initial weight loss and weight maintenance, and then subsequent weight regain over 96 weeks. METHODS: Forty-five obese women were randomly assigned to 1 of 3 treatment groups: (1) diet alone, (2) diet and aerobic training, and (3) diet and strength training. All subjects received the same 48-week group behavior modification program and diet (approximately 3879 kJ/d (approximately 925 kcal/d) for the first 16 weeks; approximately 6276 kJ/d (approximately 1,500 kca/d) thereafter). Exercising subjects were provided 3 supervised exercise sessions per week for the first 28 weeks and 2 sessions weekly until week 48. During weeks 48 to 96, subjects were unsupervised. Oral glucose tolerance tests were performed at baseline and weeks 16, 24, 44, and 96. RESULTS: Subjects across the 3 conditions achieved a mean weight loss of 13.8 kg by week 16, which was associated with decreased insulin levels (61.8% of baseline) There were no significant differences among groups in changes in body mass index, which is a measure of weight in kilograms divided by the square of the height in meters, weight, glucose tolerance, or insulin levels at weeks 16, 24, and 44. No additional beneficial effect of aerobic or strength exercise on insulin resistance, as reflected by serum insulin levels before and after a glucose load, was demonstrated. The 22 subjects who were studied at week 96 maintained a loss of approximately 10% of initial weight. Insulin levels, however, had returned to pretreatment levels. CONCLUSIONS: This study confirms the beneficial effect of weight reduction on hyperinsulinemia in obese individuals. Participation in supervised exercise did not result in additional improvement in weight loss or insulin sensitivity. We also observed a marked increase in insulin levels with only partial weight regain. Determining the amount of sustained weight loss necessary for continued improvement in insulin sensitivity will require further study.

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