Development and Validation of a Simple Equation to Fat Mass and Percentage of Body Fat in Children and Adolescents

Background: This study aimed to develop and validate a simple equation to fat mass (FM) and percentage of body fat (PBF) in children and adolescents. Methods: Participants consisted of 404 children and adolescents (176 males and 228 females, 5-18 years old) randomly divided into Derivation (n = 279) and Validation (n = 125) groups. FM and PBF were measured by a bioelectrical impedance analyzer. Based on demographic variables retrieved from the derivation group, 10 FM and 10 PBF predictive equations were developed using multiple regression. Finally, the most accurate model (using the coefficient of determination - R2) was chosen and validated on the validation group. Results: The best FM and PBF equations, which were derived from demographic characteristics, were: FM (kg) = Weight (kg) x 0.15 + BMI x 1.53 + Sex x 3.40 – Age (years) x 0.37 – 26.20; where sex = 1 for male and 0 for female. R = 0.97, R2 = 0.94, standard error of the estimate (SEE) = 3.74 kg. PBF (kg) = 0.31 x Height (cm) - Weight (kg) x 0.59 + BMI x 2.98 + Sex x 6.17 – Age (years) x 0.76 – 52.84; where sex = 1 for male and 0 for female. R = 0.90, R2 = 0.82, SEE = 4.88 kg. Conclusion: Our predictive equations accurately predicted FM and PBF using simple parameters (height, weight, BMI, sex, and age) in children and adolescents.