Prevalence and Time Trends

Nationally representative U.S. health examination surveys, in which weight and height were measured in samples of the population, date back to 1960. Beginning with the Second National Health and Nutrition Examination Survey (NHANES II) (1976-1980), the definition of overweight that has been used to compare these epidemiologic surveys has been a statistical one that corresponded to the 85th percentile of body mass index (BMI) for men and women aged 20 through 29 years in NHANES II with no particular relation to a specific increase in disease risk (45). Adults in these surveys have been categorized as overweight with a BMI 27.8 kg/m² for men and 27.3 kg/m² for women (45). The rationale for using persons aged 20 through 29 years as the reference population is supported largely by the observation that the increases in body weight after age 29 that commonly occur with aging are attributable primarily to fat accumulation (46, 47). However, the BMI levels used for the definition of overweight and obesity are somewhat arbitrary, since the relationship between body weight and disease risk is continuous with the exception of the extremely underweight: disease risk increases as weight increases.

Figure 1. Age-Adjusted Prevalence of
Overweight (BMI 25-29.9) and Obesity (BMI 30)

Source: CDC/NCHS, United States, 1960-94 (ages 20-74 years)

Figure 1 depicts data from several NHANES surveys using the panel's definition of overweight as a BMI of 25 to 29.9 kg/m² and of obesity as a BMI of 30 kg/m². From 1960 to 1994, the prevalence of overweight increased slightly from 37.8 to 39.4 percent in men and from 23.6 to 24.7 percent in women (National Center for Health Statistics/CDC) (48). In men and women together, overweight increased from 30.5 to 32.0 percent (48). During the same time period, however, the prevalence of obesity increased from 10.4 to 19.9 percent in men and from 15.1 to 24.9 percent in women. In men and women together, obesity increased from 12.8 to 22.5 percent. Most of the increase occurred in the past decade. In addition to adults, obesity in U.S. children increased markedly as well (49) (See Appendix III), and, if unchecked, portends an even greater increase in adult obesity in the future.

Table II-1shows the combined prevalence of overweight and obesity, defined as a BMI of 25.0 kg/m², among persons aged 20 to 80-plus years, by age, race/ethnicity, and gender in the United States from 1960 to 1994 (48). The increase in overweight and obesity appears to have occurred among U.S. adults across all ages, genders, and racial/ethnic groups. The most recent NHANES III surveys, conducted from 1988 to 1994, reported that 59.4 percent of men and 50.7 percent of women in the United States are overweight or obese. The prevalence is much higher in non-Hispanic Black women (66.0 percent), in Mexican-American women (65.9 percent), and in Mexican-American men (63.9 percent).

Using the definition of obesity as a BMI of 30 kg/m², Table II-2 shows that in the United States, 19.5 percent of men and 25.0 percent of women are obese (48).The prevalence of obesity is much higher in minority women, being 36.7 percent in non-Hispanic Black women and 33.3 percent in Mexican-American women.