Obesity has become a public health crisis in the United States. Currently two thirds of American adults and one third of American children and adolescents are overweight or obese ( 1 Ogden C.L. Flegal K.M. Carroll M.D. Johnson C.L. Prevalence and trends in overweight among US children and adolescents, 1999–2000. JAMA. 2002; 288: 1728-1732 Google Scholar , 2 Flegal K.M. Carroll M.D. Ogden C.L. Johnson C.L. Prevalence and trends in obesity among US adults, 1999–2000. JAMA. 2002; 288: 1723-1727 Google Scholar ). The prevalence of obesity and overweight among US children and adolescents has more than doubled since the 1970s, and it continues to increase. Minority and low socioeconomic status (SES) groups are disproportionately affected ( 1 Ogden C.L. Flegal K.M. Carroll M.D. Johnson C.L. Prevalence and trends in overweight among US children and adolescents, 1999–2000. JAMA. 2002; 288: 1728-1732 Google Scholar , 2 Flegal K.M. Carroll M.D. Ogden C.L. Johnson C.L. Prevalence and trends in obesity among US adults, 1999–2000. JAMA. 2002; 288: 1723-1727 Google Scholar , 3 Wang Y. Monteiro C. Popkin B.M. Trends of obesity and underweight in older children and adolescents in the United States, Brazil, China, and Russia. Am J Clin Nutr. 2002; 75: 971-977 Google Scholar ). The 1999-2000 National Health and Nutrition Examination Survey (NHANES) data show large differences in the prevalence of overweight between ethnic groups in children and adolescents ( 1 Ogden C.L. Flegal K.M. Carroll M.D. Johnson C.L. Prevalence and trends in overweight among US children and adolescents, 1999–2000. JAMA. 2002; 288: 1728-1732 Google Scholar ). Overall, 30.4% of US adolescents aged 12 to 19 years were overweight or at risk of overweight (body mass index [BMI]≥85th percentile), whereas the figure was 40.4% in black and 43.8% in Mexican-American adolescents compared with 26.5% in white adolescents; however, the ethnic differences were much smaller in preschool children—the prevalence was 20.6%, 19.3%, 22.7%, and 20.5%, respectively ( 1 Ogden C.L. Flegal K.M. Carroll M.D. Johnson C.L. Prevalence and trends in overweight among US children and adolescents, 1999–2000. JAMA. 2002; 288: 1728-1732 Google Scholar ). Low-SES groups were at increased risk. Previously, we found that the prevalence of overweight was 29.3%, 25.1%, and 21.7% in the low-, medium-, and high-SES groups, respectively ( 3 Wang Y. Monteiro C. Popkin B.M. Trends of obesity and underweight in older children and adolescents in the United States, Brazil, China, and Russia. Am J Clin Nutr. 2002; 75: 971-977 Google Scholar ). Y. Wang is an assistant professor, Department of Human Nutrition, University of Illinois at Chicago, Chicago, IL, USA. L. Tussing is a project coordinator, Department of Human Nutrition, University of Illinois at Chicago, Chicago, IL, USA.