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30 March 2002
Physical Activity Key To Weight Loss 
Between 1991 and 1998, the prevalence of obesity in the United States increased by almost 50%. Current research efforts are focused on the relative contributions of dietary change and physical inactivity to the increase in overweight and obesity, which together now characterize 55% of the American population. In an article published in the American Journal of Clinical Nutrition, Weinsier et al. compared the total free-living energy expenditures of normal weight women who had either maintained or gained weight over the year prior to the study. The most important factor that distinguished those who were successful from those who were unsuccessful at maintaining their weight loss was their level of physical activity. Forty-seven premenopausal white or black women, aged 20 to 46 years, were initially studied in a normal weight range, defined as a body mass index (BMI) of less than 25. About one half of the group were post-obese after a successful weight loss. All subjects were sedentary and exercised less than once per week. One year later, the women were admitted to a clinical research center for a 4-day period during which their body composition, physical fitness, energy exercise economy, and muscle strength were assessed. Two groups of women were identified, the first consisting of 20 "gainers"— who had gained an average of 9.6 kg— and the second of 27 "maintainers"— who had gained an average of .7 kg over the past year. The energy expenditure of activity was 44% higher over time in the maintainers' group than in the gainers' group,1 indicating that physical inactivity, rather than other factors such as metabolic characteristics or dietary intake, accounted for most of the difference between the two groups. The authors estimate that in order to match the low weight range of the maintainers group those who gained weight would have to engage in 80 minutes per day of moderate-intensity physical activity such as walking, using the stairs, and gardening. This suggestion is more than twice the amount of exercise recommended by the U.S. Department of Agriculture's Dietary Guidelines for Americans to maintain normal body weight after weight loss. In an accompanying editorial, Wyatt and Hill strongly advocate the promotion of increased physical activity in daily life, especially for obesity-prone individuals.
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