Effects of the Amount of Exercise on Body Weight, Body Composition, and Measures of Central Obesity

BACKGROUND: Obesity is a major health problem due, in part, to physical inactivity. The amount of activity needed to prevent weight gain is unknown. OBJECTIVE: To determine the effects of different amounts and intensities of exercise training. DESIGN: Randomized controlled trial (February 1999-July 2002). SETTING AND PARTICIPANTS: Sedentary, overweight men and women (aged 40-65 years) with mild to moderate dyslipidemia were recruited from Durham, NC, and surrounding communities. INTERVENTIONS: Eight-month exercise program with 3 groups: (1) high amount/vigorous intensity (calorically equivalent to approximately 20 miles 32.0 km of jogging per week at 65%-80% peak oxygen consumption); (2) low amount/vigorous intensity (equivalent to approximately 12 miles 19.2 km of jogging per week at 65%-80%), and (3) low amount/moderate intensity (equivalent to approximately 12 miles 19.2 km of walking per week at 40%-55%). Subjects were counseled not to change their diet and were encouraged to maintain body weight. MAIN OUTCOME MEASURES: Body weight, body composition (via skinfolds), and waist circumference. RESULTS: Of 302 subjects screened, 182 met criteria and were randomized and 120 completed the study. There was a significant (P<.05) dose-response relationship between amount of exercise and amount of weight loss and fat mass loss. The high-amount/vigorous-intensity group lost significantly more body mass (in mean SD kilograms) and fat mass (in mean SD kilograms) (-2.9 2.8 and -4.8 3.0, respectively) than the low-amount/moderate-intensity group (-0.9 1.8 and -2.0 2.6, respectively), the low-amount/vigorous-intensity group (-0.6 2.0 and -2.5 3.4, respectively), and the controls (+1.0 2.1 and +0.4 3.0, respectively). Both low-amount groups had significantly greater improvements than controls but were not different from each other. Compared with controls, all exercise groups significantly decreased abdominal, minimal waist, and hip circumference measurements. There were no significant changes in dietary intake for any group. CONCLUSIONS: In nondieting, overweight subjects, the controls gained weight, both low-amount exercise groups lost weight and fat, and the high-amount group lost more of each in a dose-response manner. These findings strongly suggest that, absent changes in diet, a higher amount of activity is necessary for weight maintenance and that the positive caloric imbalance observed in the overweight controls is small and can be reversed by a modest amount of exercise. Most individuals can accomplish this by walking 30 minutes every day.