The prevalence of obesity in the US population might be stabilizing, according to two new analyses of data from the National Health and Nutrition Examination Survey (NHANES).

The NHANES survey “is unique in that it combines interviews and physical examination,” explains Katherine Flegal, a researcher from the Centers for Disease Control and Prevention, who was involved in both studies. “Other national databases use self-reported height and weight, which can be less accurate and give lower estimates of obesity prevalence than those arrived at using measured data.”

Flegal and colleagues analyzed BMI trends and obesity prevalence among the US population between 1999 and 2010. Their analyses included new 2009–2010 data on 5,926 men and women and on a representative sample of 4,111 children and adolescents aged 0–19 years.

In 2009–2010, the estimated overall obesity prevalence among adult men and women was 35.5% and 35.8%, respectively. Over the 12 years considered in the study, the estimated obesity prevalence significantly increased among men, non-Hispanic black women and Mexican American women, but not among women in general. However, a comparison of the 2003–2008 and 2009–2010 periods showed no significant difference in this measure, which suggests that the prevalence of obesity might be leveling off.

Among children and adolescents, the estimated prevalence of obesity did not change between 2003–2008 and 2009–2010, which indicates that the stabilizing trends observed among adults are also taking place in younger age groups.

The causes of the reported trends, which might also be occurring in other countries, are not clear. Therefore, “it is hard to predict the future trends in obesity,” comment the researchers, who warn against models that make predictions solely on the basis of calendar time.

“Because of concerns about obesity and trends in obesity, we continue to track these trends using NHANES data, which are released in 2-year cycles,” concludes Flegal.