The comparison of body compsition method: TUBON project

The purpose of this research is to compare different body composition assessment methods used in children aged 6–18 years and to examine whether these methods can be used interchangeably according to age and sex. The dataset used in this study was obtained within the scope of the TÜBİTAK-SBAG Project No. 120S408 ("TUBON Project"). The study sample consisted of 6,310 children (3,253 boys and 3,057 girls). The age-group distribution was as follows: 911 participants aged 6–7.99 years, 1,228 participants aged 8–9.99 years, 2,875 participants aged 10–14.99 years, and 1,296 participants aged 15–17.99 years. Body composition was assessed using anthropometric measurements (triceps and medial calf skinfold thickness, circumference and breadth measurements), Bioelectrical Impedance Analysis (BIA) raw data, and widely used regression equations in the literature (Slaughter, Küçükkubaş, Gutiérrez-Marín, Houtkooper, Oppliger, and Schaefer). Fat-free mass (FFM) values obtained from different methods were compared using Bland–Altman analyses. The analyses focused on identifying differences and agreement levels among the methods. The findings indicated that systematic and proportional biases may exist between the Slaughter equation and other population-specific formulas, and these discrepancies increased particularly in children with higher FFM values. These results show that each method should be used in the population for which it was originally developed, and that the interchangeability of the formulas is limited. Based on the findings, it is recommended that age- and sex-specific equations be used in body composition assessments, that standardized measurement conditions be ensured when using BIA, and that anthropometric measurements be performed and interpreted by trained practitioners. The results provide an important scientific basis for method selection in field studies and clinical applications involving children and adolescents.