Obesity in U.S. Appears to Be Leveling Off



The prevalence of obesity in the United States appears to have plateaued, according to data from the 2009-2010 National Health and Nutrition Examination Survey (NHANES) conducted by the U.S. Centers for Disease Control and Prevention.

Following dramatic increases in the prevalence of obesity in adults, children, and adolescents in the 1980s and 1990s, as well as changes in the distribution of body mass index, no significant changes were seen in 2009-2010, compared with 2003-2008 figures in adults, and compared with 2007-2008 prevalence rates in children and adolescents.

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Data from the 2009-2010 National Health and Nutrition Examination Survey indicate that obesity in adults, children, and adolescents has not increased from previous figures.

For example, based on data from the 5,926 men and women with measured weight and height who participated in the 2009-2010 NHANES, the age-adjusted prevalence of obesity was roughly 35% for both men and women, which was not significantly different overall compared with the prevalence from 2003-2008, Katherine M. Flegal, Ph.D., and her colleagues from the National Center for Health Statistics, CDC, Hyattsville, Md., report online in the Jan. 17 JAMA.

Despite the lack of change overall, the analysis of adult data did indicate, however, that obesity increased in certain segments of the population. While no significant increase was seen among women overall (age- and race-adjusted annual change in odds ratio from 1999-2010, 1.01), statistically significant increases were seen among non-Hispanic black women (OR, 1.03) and Mexican American women (1.03), the investigators noted (JAMA 2012 Jan. 17 [doi:10.1001/jama.2012.39]).

A significant linear trend was also seen in men over the 12-year period (annual change in OR, 1.04).

As for BMI, the age-adjusted mean in both men and women was 28.7, and the trends over time in this study were similar to those seen with obesity, with a significant increase seen in men, but not in women, over the 12 years, the investigators said.

In a separate cross-sectional analysis of data from 4,111 children and adolescents who participated in NHANES, the 2009-2010 obesity prevalence of 9.7% in infants and toddlers up to age 2 years, and 16.9% for those aged 2-19 years, did not differ significantly from the 2007-2008 prevalence, and no difference was seen between males and females in regard to obesity prevalence, Cynthia L. Ogden, Ph.D., and her colleagues, also from the National Center for Health Statistics, CDC, reported in the same issue of JAMA.

A trend analysis over the 12-year study period did indicate, however, that the obesity prevalence among males aged 2-19 years increased significantly between 1999-2000 and 2009-2010 (OR, 1.05) per 2-year survey cycle, and that there was a significant increasing trend for non-Hispanic black males (OR, 1.10). Also, BMI increased significantly in males aged 12 through 19 years (JAMA 2012 Jan. 17 [doi:10.1001/jama.2012.40]).

NHANES data have been collected continuously since 1999, with reports released in 2-year cycles. Since no universally agreed upon definition of obesity exists for infants and toddlers up to age 2 years, high weight in this age group was defined as weight-for-recumbent length at or above the 95th percentile on the CDCs 2000 growth charts, the investigators explained.

Weight status in those aged 2 through 19 years is defined based on BMI; those at or above the sex-specific 85th percentile, but less than the 95th percentile, are considered overweight, and those at or above the sex-specific 95th percentile are considered obese. For adults, those with a BMI of 25.0 to 29.9 are considered overweight, and those with a BMI of 30.0 or higher are considered obese, with further subdivision into grades 1, 2, and 3 obesity based on BMI of 30.0 to less than 35.0, 35.0 to less than 40.0, and 40.0 or greater, respectively.

Investigators for both analyses noted that it is important to keep in mind that BMI is an "imperfect measure of body fat."

Since racial and ethnic differences in the level of body fat at specific BMIs exist, the differences in obesity prevalence by race and ethnicity in these studies may not represent actual differences in body fat, they said.

Overall, the findings in both adults and children/adolescents suggest that increases in the prevalence of obesity that have previously been observed are not continuing and have leveled off.

Although it’s difficult to predict whether these trends will continue in the same direction, the findings suggest that previous models that predict continuing increases in obesity prevalence in all age groups may be based on invalid assumptions.

None of the authors indicated having relevant conflicts of interest.

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