Rena R. Wing
Betsy A. Polley
University of Pittsburgh School of Medicine
Obesity is a significant health problem in the United States. One out of every two Americans is either overweight or obese (Flegal, Carroll, Kuczmarski, & Johnson, 1998). Obesity is a major cause of morbidity and mortality, both independently and through its association with hypertension, diabetes, and hyperlipidemia. Although genetic factors clearly play a role in obesity, the dramatic increases that are occurring in the prevalence of obesity are the result of changes in lifestyle, including changes in both intake and exercise. This chapter briefly discusses epidemiological aspects of obesity and the health and psychosocial consequences of this disease. However, it focuses primarily on the behavioral factors associated with the development of obesity and lifestyle interventions that have been developed for prevention and treatment of this major health problem.
Obesity technically means an excess of body fat, and is distinct from “overweight, ” which means an excess of body weight. However, except in rare situations, such as body builders (who may be overweight but not overfat), the two are highly related and consequently the terms are often used interchangeably.
Obesity is most commonly quantified using the Body Mass Index (BMI), which is weight in kg divided by height in meters squared. Although this measure does not actually assess body fatness, it generally is highly correlated with measures of body fat. A BMI of 25–29.9 is used to define overweight and a BMI > 30 is used to define obese (Table 15.1).
Other measures of body fatness are used primarily in research settings. These include measuring skinfold thickness with calipers, using underwater weighing to measure body density, and using dual x-ray absorptiometry to measure lean body mass (Lohman, 1992).
Obesity is a major health problem in the United States, due to its prevalence and its association with morbidity and mortality. It is estimated that one of every two Americans is overweight or obese (Flegal, et al., 1998). Obesity increases with age, peaking at about age 50, and occurs more commonly in women than in men, especially in minority women. Approximately 55% to 60% of African American women and Mexican American women, from age 40 to 60, are overweight (see Fig. 15.1).
Despite all of the recent attention to obesity, the increased public interest in exercise, and the development of new low fat products, the prevalence of obesity is increasing, not decreasing (Kuczmarski, Flegal, Campbell, & Johnson, 1994). In studies conducted between 1960 and 1980, approximately 25% of Americans were overweight. Now, 33% of Americans are overweight. The exact cause of this increased obesity is unclear. It appears that dietary intake has not increased over this period (and intake of fat has decreased), raising the possibility that the increased prevalence of obesity is due to decreases in physical activity (Heini & Weinsier, 1997).