Determining BMI cut points based on excess percent body fat in US children and adolescents

Abstract

Current cut points for overweight were derived statistically from BMI distribution. The study aimed at determining age‐, gender‐, and ethnic‐specific BMI cut points based on excess body fat in US children and adolescents aged 8–17 years, who participated in the National Health and Nutrition Examination Surveys (NHANES) 1999–2004. Excess body fat was defined as % body fat ≥ 25% in boys and ≥ 30% for girls. Receiver operating characteristic curves were used to define optimal BMI levels for excess % body fat by age, gender and ethnicity. Logarithmic regression across age groups was used to predict optimal BMI cut points. Sensitivities and specificities for the detection of elevated % body fat were compared with the 85th percentiles of the CDC BMI growth charts. Optimal BMI cut points increased with the order from non‐Hispanic white, Mexican American, to non‐Hispanic black boys; Mexican American, non‐Hispanic‐white, to non‐Hispanic‐black girls. Compared to the 85th percentiles of the CDC BMI growth charts, these optimal BMI cut points had lower sensitivities and higher specificities in boys (except for < 10‐year‐old whites) and had higher sensitivities and lower specificities in girls (except for blacks). The ethnic variation in optimal cut points based on excess % body fat suggests a more specific BMI guideline to identify children with excess body fat.