OBJECTIVE: To describe the prevalence of, and trends in, overweight and obesity in the US population using standardized international definitions.

DESIGN: Successive cross-sectional nationally representative surveys, including the National Health Examination Survey (NHES I; 1960–62) and the National Health and Nutrition Examination Surveys (NHANES I: 1971–1974; NHANES II: 1976–1980; NHANES III: 1988–94). Body mass index (BMI: kg/m 2) was calculated from measured weight and height. Overweight and obesity were defined as follows: Overweight (BMI≥ 25.0); pre-obese (BMI 25.0–29.9), class I obesity (BMI 30.0–34.9), class II obesity (BMI 35.0–39.9), and class III obesity (BMI≥ 40.0).

RESULTS: For men and women aged 20–74 y, the age-adjusted prevalence of BMI 25.0–29.9 showed little or no increase over time (NHES I: 30.5%, NHANES I: 32.0%, NHANES II: 31.5% and NHANES III: 32.0%) but the prevalence of obesity (BMI≥ 30.0) showed a large increase between NHANES II and NHANES III (NHES I: 12.8%; NHANES I, 14.1%; NHANES II, 14.5% and NHANES III, 22.5%). Trends were generally similar for all age, gender and race-ethnic groups. The crude prevalence of overweight and obesity (BMI> 25.0) for age≥ 20 y was 59.4% for men, 50.7% for women and 54.9% overall. The prevalence of class III obesity (BMI≥ 40.0) exceeded 10% for non-Hispanic black women aged 40–59 y.

CONCLUSIONS: Between 1976–80 and 1988–94, the prevalence of obesity (BMI≥ 30.0) increased markedly in the US. These findings are in agreement with trends seen elsewhere in the world. Use of standardized definitions facilitates international comparisons.