title: Impact of indexing resting metabolic rate against fat-free mass determined by different body composition models.
abstract: OBJECTIVE
  To examine the differences arising from indexing resting metabolic rate (RMR) against fat-free mass (FFM) determined using two-, three- and four-compartment body composition models.
  
  
  METHODS
  All RMR and body composition measurements were conducted on the same day for each subject following compliance with premeasurement protocols.
  
  
  METHODS
  Data were generated from measurements on 104 males (age 32.1+/-12.1 y (mean+/-s.d.); body mass 81.15+/-12.85 kg; height 179.5+/-6.5 cm; body fat 20.6+/-7.6%).
  
  
  METHODS
  Body density (BD), total body water (TBW) and bone mineral mass (BMM) were measured by hydrodensitometry, deuterium dilution and dual energy X-ray absorptiometry (DXA), respectively. These measures were used to determine two (hydrodensitometry: BD; hydrometry: TBW)-, three (BD and TBW)- and four- compartment (BD, TBW and BMM) FFM values. DXA also provided three compartment derived FFM values. RMR was measured using open circuit indirect calorimetry.
  
  
  RESULTS
  Three (body fat group: lean, moderate, high) x five (body composition determination: hydrodensitometry, hydrometry, three-compartment, DXA, four-compartment) ANOVAs were conducted on FFM and RMR kJ.kg FFM(-1).d(-1). Within-group comparisons revealed that hydrodensitometry and DXA were associated with significant (P<0.001) overestimations and underestimations of FFM and RMR kJ.kg FFM(-1).d(-1), respectively, compared with four-compartment-derived criterion values. A significant interaction (P<0.001) resulted from DXA's greater deviations from criterion values in lean subjects. While hydrometric means were not significantly (P> or =0.68) different from criterion values intraindividual differences were large (FFM: -1.5 to 2.9 kg; RMR: -6.0 to 3.2 kJ.kg FFM(-1).d(-1)).
  
  
  CONCLUSIONS
  The relationship between RMR kJ.kg FFM(-1).d(-1) and exercise status would best be investigated using three (BD, TBW)- or four (BD, TBW, BMM)-compartment body composition models to determine FFM. Other models either significantly underestimate indexed RMR (hydrodensitometry, DXA) or display large intraindividual differences (hydrometry) compared with four-compartment derived criterion values.
  
  
  BACKGROUND
  Australian Research Council (small grants scheme).
authors.affiliation: School of Pharmaceutical, Molecular and Biomedical Sciences, University of South Australia, Adelaide, Australia. joe.laforgia@unisa.edu.au
authors.forename: J
authors.initials: J
authors.lastname: LaForgia
authors.forename: G E
authors.initials: GE
authors.lastname: van der Ploeg
authors.forename: R T
authors.initials: RT
authors.lastname: Withers
authors.forename: S M
authors.initials: SM
authors.lastname: Gunn
authors.forename: A G
authors.initials: AG
authors.lastname: Brooks
authors.forename: B E
authors.initials: BE
authors.lastname: Chatterton
mesh_terms: D015502:Absorptiometry, Photon / Q000379:methods; D000273:Adipose Tissue / Q000378:metabolism; D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D001481:Basal Metabolism / Q000502:physiology*; D001823:Body Composition / Q000502:physiology*; D001834:Body Water / Q000378:metabolism; D004734:Energy Metabolism / Q000502:physiology; D006801:Humans; D007101:Immersion; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D018482:Muscle, Skeletal / Q000378:metabolism; D011237:Predictive Value of Tests; D011865:Radioisotope Dilution Technique