BODY COMPOSITION IN PRE-PUBERTAL MOROCCAN CHILDREN USING ISOTOPE DILUTION: DEVELOPMENT AND VALIDATION OF BIOELECTRICAL IMPEDANCE ANALYSIS EQUATIONS FOR PREDICTION TOTAL BODY WATER AND FAT-FREE MASS

Background/Objectives: Body composition is important as a marker of both current and future health. Bioelectric impedance analysis (BIA) is a simple and accurate method for estimating body composition, but requires valid equations obtained from calibration studies to derive total body water (TBW) and fat freemass( FFM) from electrical impedance. Equations for estimating FFM and TBW using this tool, with appropriate cross-validation, have been developed in Moroccan adolescents and adults. However none of the previous studies included Moroccan children. The aim of our study was to examine the validity of published BIA-FFM and BIA-TBW equations available in the literature in the population of study and if needed to develop a new FFM-BIA and TBW-BIA equations using deuterium dilution as the reference method. Subjects/Methods: Data were collected from 247 healthy children aged 8-11-year-old. Children were sorted by gender and age group and assigned into development and validation subgroups. The deuterium dilution was used as reference for estimating TBW and FFM. The accuracy of previous published equations was tested using Bland and Altman approach, proportional bias, pure error and effect size. BIA new equations were developed using linear regression and cross-validated using Bland and Altman approach. Results: The previous published equations tested, showed a significant absolute and proportional bias indicating that these equations would provide biased values in estimating TBW and FFM. The above the mentioned biases detected, emphasizes the need for the development of specific equations to predict TBW and FFM with a low standard error in pre-pubertal Moroccan children. The new equations derived provided non-significant proportional bias values, and better agreement than other tested equations. Bias and pure error values were 0.05 and 0.76 l for boys and -0.12 and 0.92 l for girls, for TBW equation. For FFM equation, bias values were 0.09 and -0.14, and pure errors were 1.00 kg and 1.17 kg for boys and girls, respectively. Conclusions: The new prediction equations for TBW and FFM developed in our study are the most accurate to estimate TBW and FFM in Moroccan pre pubertal children aged 8-11 years. Further studies are needed to examine the validity of those new equations in a large sample on children. Aknowledgments: This study was performed with the support of the IAEA. (Project RAF 0642).