title: Four-component model of body composition in children: density and hydration of fat-free mass and comparison with simpler models.
abstract: BACKGROUND
  Body composition in children is generally measured by 2-component (2C) models, which are subject to error arising from variation in fat-free mass (FFM) composition. The 4-component (4C) model, which divides body weight into fat, water, mineral, and protein, can overcome these limitations.
  
  
  OBJECTIVE
  The aims of our study were to 1) describe 4C model data for children aged 8-12 y; 2) evaluate interindividual variability in the hydration, bone mineral content, and density of FFM; 3) evaluate the success with which 2C models and bedside techniques measure body composition in this age group with use of the 4C model as a reference.
  
  
  METHODS
  Dual-energy X-ray absorptiometry, underwater weighing, deuterium dilution, bioelectrical impedance analysis, and anthropometry were used to determine body composition in 30 children. The contribution of methodologic error to the observed variability in the hydration and density of FFM was evaluated by using propagation of error.
  
  
  RESULTS
  Mean (+/-SD) FFM density and hydration were 1.0864+/-0.0074 kg/L and 75.3+/-2.2%, respectively, and were significantly different from adult values (P < 0.02). Relative to the 4C model, deuterium dilution and dual-energy X-ray absorptiometry showed no mean bias for fatness, whereas underwater weighing underestimated fatness (P < 0.025). Fatness determined by using skinfold-thickness and bioelectrical impedance analysis measurements along with published equations showed poor agreement with 4C model data.
  
  
  CONCLUSIONS
  Biological variability and methodologic error contribute equally to the variability of FFM composition. Our findings have major implications for bedside prediction methods used for children, traditionally developed in relation to underwater weighing.
authors.affiliation: Dunn Clinical Nutrition Centre, Cambridge, United Kingdom. J.Wells@ich.ucl.ac.uk
authors.forename: J C
authors.initials: JC
authors.lastname: Wells
authors.forename: N J
authors.initials: NJ
authors.lastname: Fuller
authors.forename: O
authors.initials: O
authors.lastname: Dewit
authors.forename: M S
authors.initials: MS
authors.lastname: Fewtrell
authors.forename: M
authors.initials: M
authors.lastname: Elia
authors.forename: T J
authors.initials: TJ
authors.lastname: Cole
mesh_terms: D000273:Adipose Tissue; D001823:Body Composition; D015992:Body Mass Index; D001834:Body Water; D015519:Bone Density; D002648:Child; D005260:Female; D006801:Humans; D008297:Male; D008954:Models, Biological; D012044:Regression Analysis; D015203:Reproducibility of Results; D013046:Specific Gravity