Independent and additive effects of energy restriction and exercise on glucose and insulin concentrations in sedentary overweight men

Background: Overweight and inactivity are associated with impaired glucose tolerance, reduced insulin sensitivity, and diabetes. Few controlled trials have assessed the independent and combined effects of energy restriction and exercise on the prevention of these conditions. Objective: The objective was to evaluate the independent and additive effects of 16 wk of energy restriction and exercise on glucose and insulin concentrations. Design: Sixty nonsmoking, overweight, sedentary men aged 20-50 y were randomly assigned to either maintain or restrict their energy intake (4186-6279 kJ/d). Within each of these arms, the subjects were further randomly assigned to either a light-intensity (control) or a vigorous-intensity exercise program for 30 min 3 times/wk. Results: Fifty-one subjects completed the study. Maximal oxygen uptake increased (approximate to24%; P < 0.001) with vigorous but not with light exercise. Significant weight loss was observed with energy restriction ((x) over bar: 10.12 kg; 95% Cl: 8.02, 12.22 kg; P < 0.001) but not with exercise. Vigorous exercise reduced fasting glucose and glucose and insulin areas under the curve (AUCs) by 13% (P = 0.01) and 20% (P = 0.02), respectively. Exercise effects were independent of weight change. Energy restriction resulted in a 40% reduction in the insulin AUC (P = 0.01). Vigorous exercise and energy restriction were additive in reducing the insulin AUC. Conclusions: Energy restriction and vigorous exercise independently and additively reduce glucose and insulin concentrations in response to an oral-glucose-tolerance test. Both of these lifestyle interventions provide a potent strategy that should be an integral part of any program to reduce the risk of impaired glucose tolerance, insulin resistance, and diabetes in overweight and sedentary persons.