title: Comparative assessment of change in fat mass using dual X-ray absorptiometry and air-displacement plethysmography.
abstract: OBJECTIVE
  To compare the accuracy of body composition measurements to small, defined changes in fat mass between dual X-ray absorptiometry (DXA) and air-displacement plethysmography (ADP).
  
  
  METHODS
  Fifty-six healthy adults, 29 women and 27 men (age, 38 ± 12.4 years; BMI, 27.6 ± 5.8 kg/m2) were included in the study. Exclusion criteria were pregnancy, indwelling metal hardware or pacemakers, or weight exceeding DXA table limit (>350 lbs). All individual testing was completed within a 2-hour period. Fat packets were prepared using lard wrapped in plastic and applied exogenously in defined locations. Each participant completed body composition measurements with ADP and DXA (both testing modalities completed with and without 1 kg of exogenously applied fat mass).
  
  
  RESULTS
  Both DXA and ADP were highly accurate in detecting an overall increase in body mass associated with exogenously applied 1kg of fat mass (0.99 kg vs. 0.97 kg, respectively). DXA more accurately detected exogenous fat increase as fat mass compared to ADP (0.93 kg; 90% CI for the mean of the difference: 0.83 to 1.03 kg vs. 0.45 kg; 90% CI: 0.19 to 0.71 kg, respectively). The accuracy of body mass detection was similar for males and females (0.97 vs. 1.02 for DXA and 0.92 vs. 1.02 for ADP, respectively), though accuracy in detecting added mass as fat was less accurate in males than females (0.84 vs. 1.00 for DXA and 0.39 vs. 0.51 for ADP, respectively).
  
  
  CONCLUSIONS
  Both DXA and ADP are accurate in detecting an overall increase in body mass associated with exogenously applied 1kg of fat mass. However, DXA is more accurate than ADP in correctly identifying the increase in body mass as fat mass, as opposed to fat free mass.
authors.affiliation: Department of Pediatrics, Division of Gastroenterology, Vanderbilt University Medical Center, Nashville, Tennessee, USA.
authors.forename: Joshua
authors.initials: J
authors.lastname: Warolin
authors.affiliation: Department of Pediatrics, Division of Gastroenterology, Vanderbilt University Medical Center, Nashville, Tennessee, USA.
authors.forename: Jeff
authors.initials: J
authors.lastname: Kantor
authors.affiliation: Department of Medicine, Division of Gastroenterology, Vanderbilt University Medical Center, Nashville, Tennessee, USA.
authors.forename: Lauren E
authors.initials: LE
authors.lastname: Whitaker
authors.affiliation: Department of Biostatistics, Vanderbilt University Medical Center, Nashville, Tennessee, USA.
authors.forename: Leena
authors.initials: L
authors.lastname: Choi
authors.affiliation: Department of Pediatrics, Division of Gastroenterology, Vanderbilt University Medical Center, Nashville, Tennessee, USA.
authors.forename: Sari
authors.initials: S
authors.lastname: Acra
authors.affiliation: Department of Medicine, Division of Gastroenterology, Vanderbilt University Medical Center, Nashville, Tennessee, USA.
authors.forename: Maciej S
authors.initials: MS
authors.lastname: Buchowski