Several weight-loss predictors are associated with age or aging. Age, therefore, potentially confounds many associations of other population characteristics with weight-management variables. The average pattern of weight change shifts from a tendency to gain weight in youth and middle age to a net loss of weight after age 50 or 60 (Williamson et al., 1990). However, decreases in lean body mass and metabolic rate that occur with aging in most older adults may decrease their ability to lose weight when they attempt it (Tzankoff and Norris, 1977; Vaughn et al., 1991). The prevalence of dieting decreases as age increases (Piani and Schoenborn, 1993; Schoenborn, 1988), but at least two surveys indicate that the duration of dieting among persons trying to lose weight is longer in older persons (Levy and Heaton, 1993; Williamson et al., 1992). Sedentary behavior, health problems, and functional limitations increase with aging (King et al., 1992). Thus, older persons who enroll in treatment programs may be less likely to adopt or adhere to exercise regimens. Motivations for weight loss at older ages may shift more toward concerns for health instead of appearance (Hayes and Ross, 1987).
Although obesity among whites varies with demographic categories and may be related to ethnic origins, the high prevalence of obesity in several racial/ethnic minority populations in the United States is striking, especially among women (Kumanyika, 1994). Obesity affects up to 80 percent of adults in some age groups among black, Hispanic, Native American, and Pacific Islander populations. The high prevalence of obesity in these populations, compared to less overweight populations, may reflect greater problems with avoiding weight gain or with losing weight. Associations of race/ethnicity with weight may include the effects of low socioeconomic status (which predisposes females to obesity) (Sobal and Stunkard, 1989), pregnancy-related weight gains (Dawson and Thompson, 1990), dieting motivations and practices, lower levels of leisure-time physical activity (King et al., 1992), and residence in the southern United States (Piani and Schoenborn, 1993; Schoenborn, 1988).
Stress, which was noted earlier in this chapter as a negative predictor of weight loss, may predispose susceptible individuals to abdominal obesity through negative health-related behaviors and neuroendocrine disturbances (Björntorp, 1993). Race, ethnicity, and low socioeconomic status are associated with numerous potential sources of stress (e.g., discrimination, living in substandard housing, and being unable to afford basic necessities). However, whether excess stress is a mediator of these