Development and Validation of a Predictive Equation for Lean Body Mass in Children and Adolescents

Background: Lean body mass (LBM) is not easy to measure directly in the field or clinical setting. Equations to predict LBM from simple anthropometric measures, which account for the differing contributions of fat and lean to body weight at different ages and levels of adiposity, would be useful to both human biologists and clinicians. Aim: To develop and validate equations to predict LBM in children and adolescents across the entire range of the adiposity spectrum. Subjects and methods: Dual energy X-ray absorptiometry was used to measure LBM in 836 healthy children (437 females) and linear regression was used to develop sex-specific equations to estimate LBM from height, weight, age, body mass index (BMI) for age z-score and population ancestry. Equations were validated using bootstrapping methods and in a local independent sample of 332 children and in national data collected by NHANES. Results: The mean difference between measured and predicted LBM was -0.12% (95% limits of agreement -11.3% to 8.5%) for males and -0.14% (-11.9% to 10.9%) for females. Equations performed equally well across the entire adiposity spectrum, as estimated by BMI z-score. Validation indicated no over-fitting. LBM was predicted within 5% of measured LBM in the validation sample. Conclusion: The equations estimate LBM accurately from simple anthropometric measures.