Abstract P288: Utility of BMI in Determining Excess Adiposity in Children and Adolescents Across the Obesity Spectrum: NHANES 1999-2006
Introduction: Excess adiposity in youth is associated with a number of cardiometabolic complications. However, normative data defining excess adiposity cut-points utilizing gold-standard measures of adiposity [e.g. dual energy X-ray absorptiometry (DXA)] are lacking in youth. Moreover, the proportion of youth within a given BMI-based obesity category with excess adiposity is not well described. Therefore, we generated pediatric body fat distribution curves using DXA data from the National Health and Nutrition Examination Survey (NHANES) to identify cut-points and evaluate the accuracy of BMI in determining excess adiposity among youth.
Hypothesis: A high proportion of youth with severe obesity using BMI based definitions (class 2 and 3) will have excess adiposity as measured by DXA. Heterogeneity and misclassification will be increasingly common across youth with obesity (class 1), overweight, and normal-weight.
Methods: DXA data from NHANES 1999-2006 (Males (M) = 5,933; Females (F) = 4,532) were utilized for this analysis. Normal-weight (<85th BMI-percentile), overweight (≥85th-<95th BMI-percentile), class 1 obesity (≥95th BMI-percentile-<1.2 times the 95th percentile), class 2 obesity (≥1.2-<1.4 times the 95th BMI-percentile), and class 3 obesity (≥1.4 times the 95th percentile) were defined using Center for Disease Control based definitions for age and sex. Excess adiposity was defined using cohort-specific cut-points of the 75th, 85th, and 90th percentile for DXA-derived body fat by age and sex determined using quantile regression models with natural cubic splines (df=6).
Results: Nearly all youth with class 3 obesity (100% M, 100% F; 97% M, 99.3% F; and 94.7% M, 95.9% F; for 75th, 85th, and 90th DXA-percentile respectively) and a high proportion of those with class 2 obesity (98% M, 99% F; 92.2% M, 90.6% F; and 76.2% M, 76.3% F; for 75th, 85th, and 90th DXA-percentile respectively) had excess adiposity. A high degree of discordance was observed between BMI and DXA-derived excess adiposity among youth with class 1 obesity (81.4% M, 85.5% F; 52.7% M, 59.6% F; and 32.9% M, 36.9% F; for 75th, 85th, and 90th DXA-percentile respectively). Only a small proportion of youth with overweight or normal weight had excess adiposity.
Conclusions: The vast majority of youth with severe obesity defined by BMI-based obesity categories have excess adiposity, regardless of the cut-point used. Significant discordance was observed between DXA-derived excess adiposity in youth with obesity and overweight suggesting a high degree of misclassification using BMI-based definitions.
Author Disclosures: J.R. Ryder: None. A. Kaiser: None. K.D. Rudser: None. S.R. Daniels: None. A.S. Kelly: None.
- © 2016 by American Heart Association, Inc.