title: Impact of body-composition methodology on the composition of weight loss and weight gain.
abstract: OBJECTIVE
  We intended to (i) to compare the composition of weight loss and weight gain using densitometry, deuterium dilution (D₂O), dual-energy X-ray absorptiometry (DXA), magnetic resonance imaging (MRI) and the four-compartment (4C) model and (ii) to compare regional changes in fat mass (FM), fat-free mass (FFM) and skeletal muscle as assessed by DXA and MRI.
  
  
  METHODS
  Eighty-three study participants aged between 21 and 58 years with a body mass index range of 20.2-46.8 kg/m(2) had been assessed at two different occasions with a mean follow-up between 23.5 and 43.5 months. Body-weight changes within < 3% were considered as weight stable, a gain or a loss of >3% of initial weight was considered as a significant weight change.
  
  
  RESULTS
  There was a considerable bias between the body-composition data obtained by the individual methods. When compared with the 4C model, mean bias of D₂O and densitometry was explained by the erroneous assumption of a constant hydration of FFM, thus, changes in FM were underestimated by D₂O but overestimated by densitometry. Because hydration does not normalize after weight loss, all two-component models have a systematic error in weight-reduced subjects. The bias between 4C model and DXA was mainly explained by FM% at baseline, whereas FFM hydration contributed to additional 5%. As to the regional changes in body composition, DXA data had a considerable bias and, thus, cannot replace MRI.
  
  
  CONCLUSIONS
  To assess changes in body composition associated with weight changes, only the 4C model and MRI can be used with confidence.
authors: Institute of Human Nutrition and Food Science, Christian-Albrechts University, Kiel, Germany.
authors: M
authors: M
authors: Pourhassan
authors: B
authors: B
authors: Schautz
authors: W
authors: W
authors: Braun
authors: C-C
authors: CC
authors: Gluer
authors: A
authors: A
authors: Bosy-Westphal
authors: M J
authors: MJ
authors: Müller
mesh_terms: D015502:Absorptiometry, Photon / Q000379:methods; D000273:Adipose Tissue; D000328:Adult; D015982:Bias; D001823:Body Composition; D001825:Body Fluid Compartments; D015992:Body Mass Index; D001834:Body Water; D001837:Body Weights and Measures / Q000379:methods*; D003720:Densitometry / Q000379:methods; D017666:Deuterium Oxide; D017097:Electric Impedance; D005260:Female; D006801:Humans; D007201:Indicator Dilution Techniques; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal; D009765:Obesity; D015430:Weight Gain; D015431:Weight Loss
chemical_list: D017666:Deuterium Oxide