chapter  42
Physical Activity, Obesity, and Health Outcomes
Pages 22

As documented by recent national and international guidelines, obesity is a significant public health problem (1,2). The prevalence of overweight and obesity is increasing in many countries around the world. In the United States it is estimated that at least 55% of adults are overweight or obese (defined as a body mass index [BMI] z25 kg/m2), and according to recent surveys, the prevalence of obesity (BMI z30 kg/m2) in the United States increased from 12% to 19.8% between 1991 and 2000 (1,3,4). Low levels of energy expenditure from physical activity are likely a major contributing factor to the rapid increase in the prevalence of obesity (5-7). Although there are no direct data, it seems probable that a decline in energy expenditure has taken place due to obvious changes in occupational-and householdrelated physical activity, as well as urban environments that are increasingly less conducive to leisure-time physical activity.