Obesity rates have leveled off and even started to decline for many adolescents, but not certain racial and ethnic minorities, according to a new study. 

The study says it is the first to find significant differences in obesity trends over time by race and ethnicity and this evidence of increasing racial disparities for obesity underscores the need for more tailored intervention programs and policies that target high-risk groups, the authors conclude.

Kristine Madsen, MD, MPH, an assistant professor of pediatrics at U.C. San Francisco, and co-authors examined trends in the prevalence of high body mass index (BMI) among Hispanic, non-Hispanic white, Asian, black, and American Indian adolescents in California from 2001 through 2008. BMI is a measure of body fat based on a person's height and weight that is commonly used to screen for obesity. Generally, children are considered obese if they have a BMI at or above the 95th percentile, and severely obese if their BMI score is at or above the 99th percentile.

The data published in Pediatrics revealed that obesity rates at the 95th percentile declined or stabilized among a number of groups during the time period studied. Among white and Asian girls and boys, obesity rates peaked in 2005, then declined over the next three years, with 2008 rates coming in at 12 percent for white youth and 13 percent for Asians. Overall rates for Hispanic youth also peaked in 2005 and then leveled off at 26 percent through 2008; although Hispanic boys did show a small decline on their own. Rates among black boys stayed at the same level each year.

However, from 2001 through 2008, the prevalence of obesity continued to climb for black and American Indian girls, reaching 22 percent and 23 percent, respectively. Furthermore, these two groups were more than three times as likely as white girls to be severely obese, with a BMI at the 99th percentile.

When comparing groups at the 99th BMI percentile, the researchers found that only Asian youth and white boys showed any signs of decline after 2005. All other groups – including Hispanic boys and girls, white girls, black boys and girls, and American Indian boys and girls – peaked in 2005 and then remained at a plateau through 2008.

"When you look at the very heaviest end of the spectrum, the picture is pretty bleak, and we do not yet know if severe obesity rates for these groups will remain at a plateau or continue to increase," Madsen added.

The researchers analyzed the health records of more than eight million fifth-, seventh-, and ninth-grade students in California who underwent the state's mandatory school-based BMI screening. Among the students studied, 46.4 percent were Hispanic, 32.8 percent were white, 12.6 percent were Asian, 7.7 percent were black, and 0.5 percent were American Indian.

According to the researchers, the study's large and highly diverse group of subjects is a unique strength. And, although the data were confined to one state, the results show population level trends that are applicable elsewhere, since about one in eight children in the United States currently live in California.

"We need to focus on implementing real change in the places where kids spend most of their time – at home, at school and in the after-school arena – to encourage healthier habits and reduce consumption," Madsen said. "Priorities must be reconsidered so that health is not an afterthought."

Citation: Kristine A. Madsen, Ashley E. Weed, Patricia B. Crawford, 'Disparities in Peaks, Plateaus, and Declines in Prevalence of High BMI Among Adolescents', Published online August 16, 2010 PEDIATRICS doi:10.1542/peds.2009-3411