Physical activity, body weight, and adiposity: an epidemiologic perspective.

Overweight is a common problem in the United States, especially among minority women and persons of lower socioeconomic status and lower educational attainment. Moreover, the prevalence of reported inactivity may be highest in these same population subgroups. Both overweight and sedentary behavior are important risk factors for chronic disease morbidity and mortality; however, there is encouraging evidence that moderate to higher levels of physical activity may provide protection from certain chronic diseases, even among persons with established risk factors. Several methodological issues preclude the ability to determine accurately the impact of physical activity on body weight and adiposity. These issues include (a) a low prevalence of higher-intensity physical activity in the general population, (b) measurement error with regard to self-reported activity, especially that of lower-intensity, (c) inappropriate time frame of the physical activity assessment, (d) effect modification by age and gender, and (e) failure to adjust for important statistical confounders. Despite these methodological issues, the inverse association between physical activity and weight has been reported in several cross-sectional epidemiologic studies, which consistently report lower body weight, or more favorable distribution of body fat, with higher categorical levels of self-reported physical activity. Directionality of the physical activity and weight relation cannot be determined from these studies, however, and the few longitudinal epidemiologic studies that have assessed the influence of physical activity on the risk of weight gain report inconclusive results. This is possibly because a one-time assessment of physical activity if not adequate in describing the contribution of habitual physical activity on long-term weight maintenance. Therefore, longitudinal population-based studies with multiple assessments of physical activity over long follow-up periods are necessary to determine this relationship. In any case, the evidence suggests that persons concerned with overweight, or especially the prevention of overweight and obesity, should increase their physical activity. Sociodemographic characteristics such as age, gender, educational level, and weight are associated with physical activity patterns and choices. Therefore, these characteristics should be considered by professionals when implementing physical activity interventions for weight control. Walking is accessible to all segments of the U.S. population. Because walking is convenient, low cost, and safe, and can result in weight loss if done regularly for durations of at least 20-30 min, its relative merits should be stressed in weight reduction and maintenance programs. Furthermore, to reduce the morbidity and mortality associated with overweight, obesity, and sedentary behavior, priority for intervention programs should be directed at persons in the most vulnerable sectors of the population.