Nearly one in five young people in the United States are obese, and proportionally more adolescents have been obese during every time period measured since 1994, according to an analysis published online June 7 in JAMA.

But the most recent data suggest only a “small” rise in adolescent obesity since 2011, and stable rates among children during this time period, said Cynthia L. Ogden, Ph.D., of the National Center for Health Statistics at the Centers for Disease Control and Prevention.

Few studies of obesity in young people have teased out rates by age, according to Dr. Ogden and her associates. Using National Health and Nutrition Examination Survey data, they calculated rates of obesity and extreme obesity among 40,780 children and adolescents aged 2-19 years for the periods 1988-1994 through 2013-2014. They defined obesity as a body mass index (BMI) at or above the sex-specific 95th percentile on the CDC BMI-for-age growth charts, and they defined extreme obesity as a BMI at least 120% of the sex-specific 95th percentile on the charts ( JAMA. 2016 Jun 7. doi: 10.1001/jama.2016.6361 ).

Based on these definitions, 17% of children and adolescents were obese between 2011 and 2014, while 6% were extremely obese, the investigators reported. Furthermore, 21% of adolescents were obese in 2013-2014, compared with 17% during 2003-2004 and 11% during 1988-1994.

Rates for 6- to -11-year-olds have remained fairly stable in the high teens for more than a decade, while rates among 2- to 5-year-olds peaked in 2003-2004 at nearly 14% before dropping to about 9% during 2013-2014. The prevalence of obesity varied little by sex, but diverged substantially by race and ethnicity. For example, in 2011-2014, 23% of Hispanics and about 23% of black children were obese, and 9% and 12% were extremely obese, respectively the researchers reported. Rates for the same ages of non-Hispanic Asian children were 9% and 2%, respectively, and those for non-Hispanic whites were 20% and 7%, respectively.

“Body mass index is an imperfect measure of body fat and health risk,” the investigators cautioned. “There are racial and ethnic differences in body fat at the same BMI level. Among children and adolescents, the definition of obesity is statistical. Children and adolescents are compared with a group of U.S. children in the 1960s to early 1990s, so the prevalence of obesity is dependent on the characteristics of the age-specific population during that period. In addition, among young children, small changes in weight can lead to relatively large changes in BMI percentile”

The researchers reported no funding sources and had no disclosures.