Overweight American children and adolescents have become fatter over the last decade, according to researchers at the Johns Hopkins Bloomberg School of Public Health and National Institute on Aging (NIA). They examined adiposity（肥胖） shifts across socio-demographic（人口统计学的） groups over time and found U.S. children and adolescents had significantly increased adiposity measures such as body mass index (BMI身体质量指数), waist circumference（腰围） (WC) and triceps（三头肌） skinfold（皮肤褶） thickness (TST). The increases in adiposity were more pronounced in some sex-ethnic groups such as black girls. In addition, these groups gained more abdominal fat over time, which was indicated by waist size and posed greater health risks than elevated BMI. Their results are featured in the August 2010 issue of the International Journal of Pediatric Obesity. "Our analysis shows that the increase in adiposity among U.S. children and adolescents was unequally distributed across socio-demographic groups and across the spectrum of BMI, waist circumference and triceps skinfold thickness measures," said Youfa Wang, MD, PhD, senior author of the study and an associate professor in the Bloomberg School's Department of International Health. "Heavier children and adolescents gained more adiposity, especially waist size, and these findings were most significant among children ages 6 to 11. Ethnic disparities in mean BMI have also increased substantially when comparing black girls with their white counterparts for all ages combined. Solely examining the changes in the prevalence of overweight and obesity based on fixed BMI cut points could not gain such important insights regarding shifts in the obesity epidemic."

To examine these changes over time, researchers conducted a comprehensive analysis of nationally representative survey data（测量数据） collected from the National Health and Nutrition Examination Survey (NHANES) since the late 1980s. They examined the changes in American boys and girls ages 2 to 19, as well as by ethnic groups at the population level.

"Our research suggests that U.S. young people may be at greater obesity-related risks than what was revealed by increases in BMI, as waist circumference is a better predictor of future health risks, such as for type 2 diabetes（糖尿病） and heart disease in adults," said May A. Beydoun, PhD, staff scientist, National Institute on Aging, HIH/IRP, and a former postdoctoral fellow in the Bloomberg School's Department of International Health. "More vigorous efforts should be made to understand the underlying causes. Moving forward, this could help guide future population-based interventions including those focusing on the total population and those targeting vulnerable or genetically susceptible groups."

"Socio-demographic disparities（不同，不一致） in distribution shifts over time in various adiposity measures among American children and adolescents: What changes in prevalence rates could not reveal" was written by May A. Beydoun and Youfa Wang.