Nearly All US Youth With BMI-Defined Obesity Have Excess Adiposity

The prevalence of body mass index (BMI)-defined obesity (BDO) among US youth aged 8 to 19 years closely mirrored that of BDO with excess adiposity across age, sex, and race and ethnicity, according to a research letter published today in JAMA Pediatrics.1

BMI can both underestimate and overestimate adiposity, defined as the accumulation of excess body fat.2 Because of this, an international expert commission recommends confirming obesity diagnoses with at least 2 anthropometric measures (BMI, waist-to-height ratio, waist circumference) or direct body fat measurement.

In adults, confirming excess adiposity rarely changes BDO prevalence, raising questions about the clinical value of this approach.3 However, the researchers noted that its relevance in children and adolescents remains unclear.1

Consistent across age, sex, and race, BMI closely mirrored body fat–based obesity in nearly all US youth with BMI-defined obesity (BDO). | Image Credit: Vitalii Vodolazskyi - stock.adobe.com

To examine this, they conducted a cross-sectional study using pooled data from US children and adolescents aged 8 to 19 years in the 2015-2016 and 2017-2018 cycles of the National Health and Nutrition Examination Survey (NHANES), comparing excess adiposity across BMI categories. Participants missing data on body weight, height, waist circumference, or dual-energy x-ray absorptiometry (DEXA) measurements were excluded.

BDO was defined as a BMI at or above the 95th percentile for age and sex, including class 2 (BMI 120% and < 140% of the 95th percentile) and class 3 (BMI 140% or more of the 95th percentile) obesity. Meanwhile, commission-defined obesity (CDO) was defined as excess adiposity based on at least 2 elevated anthropometric measures (BMI, waist-to-height ratio, or waist circumference) or an elevated body fat percentage.

Thresholds were established based on associations with clinical outcomes: a waist-to-height ratio of 0.5 or greater, a waist circumference at or above the 90th percentile for age and sex, and a body fat percentage of 25% or greater for males and 35% or greater for females. The researchers then estimated the prevalence of BDO, BDO with excess adiposity (both BDO and CDO), and CDO among youth with BDO. They also calculated the proportions of youth with CDO and within each BMI category.

The study population consisted of 3194 participants, most of whom were male (n = 1671; 52%), with a weighted mean (SD) age of 13 (3) years. By race and ethnicity, 1017 were Hispanic, 928 were White, 679 were Black, 313 were Asian, and 257 were multiracial or other races or ethnicities.

The prevalence of BDO was 20.1% (95% CI, 18.0%-22.3%), while the prevalence of BDO with CDO was 20.0% (95% CI, 17.8%-22.2%), meaning 99.5% (95% CI, 99.0%-100%) of those with BDO also had CDO; these results were consistent across sex, age, and race and ethnicity.

Additionally, the overall prevalence of CDO was 46.2% (95% CI, 43.6%-48.9%). The researchers found that all individuals with class 2 or 3 BDO had CDO. In comparison, 99.3% (95% CI, 98.4%-100%) of those with class 1 BDO, 74.9% (95% CI, 70.3%-79.4%) of overweight youth, 22.2% (95% CI, 19.5%-24.8%) of those with a normal BMI, and 5.2% (95% CI, 0%-10.8%) of individuals considered underweight had CDO.

“While nearly all youth with BDO had CDO by elevated anthropometric measures and by elevated body fat percentage, nearly all youth who had CDO without BDO had an elevated body fat percentage alone,” the authors wrote.

The researchers also acknowledged their study’s limitations, including the exclusion of children younger than 8, partly because NHANES did not collect DEXA measurements for this age group. Still, they expressed confidence in their findings.

“The overall prevalence of CDO was more than double the prevalence of BDO because three-quarters of youth with overweight and one-fifth of youth with normal BMI had elevated body fat percentage by DEXA,” the authors concluded. “However, widespread DEXA measurement is currently impractical, and the clinical significance of elevated body fat percentage in youth with overweight or normal BMI is unclear.”

References

1. Chetty AK, Nugent JT, Fenick AM, Sharifi M. Prevalence of excess adiposity by body mass index category among US children and adolescents. JAMA Pediatr. Published online November 3, 2025. doi:10.1001/jamapediatrics.2025.4291
2. Rubino F, Cummings DE, Eckel RH, et al. Definition and diagnostic criteria of clinical obesity. Lancet Diabetes Endocrinol. 2025;13(3):221-262. doi:10.1016/S2213-8587(24)00316-4
3. Aryee EK, Zhang S, Selvin E, Fang M. Prevalence of obesity with and without confirmation of excess adiposity among US adults. JAMA. 2025;333(19):1726-1728. doi:10.1001/jama.2025.2704