Development of youth percent body fat standards using receiver operating characteristic curves.

BACKGROUND Few studies have identified health-related criterion standards of percent body fat (%BF) in U.S. youth. Further, existing standards are static thresholds (e.g., 25%, 30%) and do not account for normal growth and maturation. PURPOSE The purpose of this study was to identify thresholds of %BF in youth linked to metabolic syndrome in a large sample of U.S. children and adolescents. METHODS Percent fat was derived from the skinfold thicknesses of those aged 12-18 years, from the National Health and Nutrition Examination Survey (NHANES [1999-2004, N=1966]). Metabolic syndrome was classified using previously published standards based on the National Cholesterol Education Program/Adult Treatment Panel III adult values at age 20 years. Using %BF z-scores as the test and metabolic syndrome as the criterion, receiver operating characteristic (ROC) curve analysis was used to identify %BF thresholds. RESULTS ROC analysis indicated that %BF can be used with moderate accuracy to identify metabolic syndrome in adolescents. %BF thresholds of 22.3% and 35.1% in boys and 31.4% and 38.6% in girls (at age 18 years) were found to be indicative of "low" and "high" metabolic syndrome risk. CONCLUSIONS Age- and gender-specific %BF thresholds for creating separate risk groups were identified in relation to metabolic syndrome status. The selected thresholds identify adolescents with unfavorable metabolic profiles. These values could be extrapolated to younger children using previously created %BF centiles, which potentially allows for earlier identification and intervention of at-risk youth if tracking of current %BF was maintained.