with a higher prevalence among poor women (46%) (NCHS, 1998a). A clear gradient with family income exists for the prevalence of overweight in women (but not in men). Poor women are 1.4 times more likely to be overweight than are middle-income women and 1.6 times more likely to be overweight than are women with high incomes (NCHS, 1998a). Obesity is particularly common among Hispanic, African American, Native American, and Pacific Islander women (USDHHS, 2000).

Populations also differ in amount of physical activity. The proportion of the population reporting no leisure-time physical activity is higher among women than men, among Hispanics than among Whites, among older than younger adults, and among the less affluent than the wealthier (USDHHS, 1996, 2000). A sedentary lifestyle is less likely with increasing income. African American men living in poverty are 3 times more likely to be sedentary than were those with high family incomes. For Hispanic and non-Hispanic White men, a sedentary lifestyle was about 2.5 times more prevalent among the poor than among those with a higher family income. Women had similar income-related gradients in sedentary lifestyle, with higher income groups experiencing a lower prevalence of sedentary lifestyle (NCHS, 1998a).

Adult Weight Gain

Adult weight gain is observed in many industrialized societies. Because full adult height generally is attained by age 18, weight gain in adulthood is almost exclusively through the addition of adipose tissue. Lack of weight gain, particularly among men over 50, does not imply an absence of gain in fat. Above this age, muscle mass is, to varying degrees, redistributed to fat, much of it within the abdomen (Rimm et al., 1995).

Avoiding weight gain as an adult is a high priority because treatment of obesity has poor long-term success, and lost weight often is regained (Chapter 5). Several studies show that greater leisure-time physical activity is associated with lower weight gain (Ravussin et al., 1988; Rissanen et al., 1991), and it reduces the weight gain often observed after cessation of cigarette-smoking (Kawachi et al., 1996). Although many people try to lose weight, most regain the weight within 5 years (NIH, 1993; USDHHS, 2000). In order to maintain weight loss, permanent lifestyle changes that combine good dietary habits, decreased sedentary behavior, and increased physical activity are essential. Changes in the physical and social environment can help people maintain the necessary long-term lifestyle changes

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