title: Bioelectrical impedance analysis to estimate body composition, and change in adiposity, in overweight and obese adolescents: comparison with dual-energy x-ray absorptiometry.
abstract: BACKGROUND
  There is a need for a practical, inexpensive method to assess body composition in obese adolescents. This study aimed to 1) compare body composition parameters estimated by a stand-on, multi-frequency bioelectrical impendence (BIA) device, using a) the manufacturers' equations, and b) published and derived equations with body composition measured by dual-energy x-ray absorptiometry (DXA) and 2) assess percentage body fat (%BF) change after a weight loss intervention.
  
  
  METHODS
  Participants were 66 obese adolescents, mean age (SD) 12.9 (2.0) years. Body composition was measured by Tanita BIA MC-180MA (Tanita BIA8) and DXA (GE-Lunar Prodigy). BIA resistance and reactance data at frequencies of 5, 50, 250 and 500 kHz, were used in published equations, and to generate a new prediction equation for fat-free mass (FFM) using a split-sample method. Approximately half (n = 34) of the adolescents had their body composition measured by DXA and BIA on two occasions, three to nine months apart.
  
  
  RESULTS
  The correlations between FFM (kg), fat mass (kg) and %BF measured by BIA and DXA were 0.92, 0.93 and 0.78, respectively. The Tanita BIA8 manufacturers equations significantly (P < 0.001) overestimated FFM (4.3 kg [-5.3 to 13.9]) and underestimated %BF (-5.0% [-15 to 5.0]) compared to DXA. The mean differences between BIA derived equations and DXA measured body composition parameters were small (0.4 to 2.1%), not significant, but had large limits of agreements (~ ±15% for FFM). After the intervention mean %BF loss was similar by both methods (~1.5%), but with wide limits of agreement.
  
  
  CONCLUSIONS
  The Tanita BIA8 could be a valuable clinical tool to measure body composition at the group level, but is inaccurate for the individual obese adolescent.
authors.forename: Ching S
authors.initials: CS
authors.lastname: Wan
authors.forename: Leigh C
authors.initials: LC
authors.lastname: Ward
authors.forename: Jocelyn
authors.initials: J
authors.lastname: Halim
authors.forename: Megan L
authors.initials: ML
authors.lastname: Gow
authors.forename: Mandy
authors.initials: M
authors.lastname: Ho
authors.forename: Julie N
authors.initials: JN
authors.lastname: Briody
authors.forename: Kelvin
authors.initials: K
authors.lastname: Leung
authors.forename: Chris T
authors.initials: CT
authors.lastname: Cowell
authors.affiliation: Institute of Endocrinology & Diabetes, The Children's Hospital at Westmead, Locked Bag 4001, Westmead NSW2145, Australia. sarah.garnett@health.nsw.gov.au.
authors.forename: Sarah P
authors.initials: SP
authors.lastname: Garnett
mesh_terms: D015502:Absorptiometry, Photon; D000293:Adolescent; D001823:Body Composition; D002648:Child; D017097:Electric Impedance; D005260:Female; D006801:Humans; D008297:Male; D009765:Obesity / Q000503:physiopathology*; D050177:Overweight / Q000503:physiopathology*