title: Bioelectrical impedance underestimates total and truncal fatness in abdominally obese women.
abstract: OBJECTIVE
  To compare estimates of total and truncal fatness from eight-electrode bioelectrical impedance analysis equipment (BIA(8)) with those from DXA in centrally obese women. The secondary aim was to examine BMI and waist circumference (WC) as proxy measures for percentage total body fat (%TBF) and truncal body fat percentage (tr%BF).
  
  
  METHODS
  This was a cross-sectional study of 136 women (age, 48.1 +/- 7.7 years; BMI, 30.4 +/- 2.9 kg/m(2); %TBF(DXA), 46.0 +/- 3.7%; WC, 104 +/- 8 cm). Fatness was measured by DXA and Tanita BC-418 equipment (Tanita Corp., Tokyo, Japan). Agreement among methods was assessed by Bland-Altman plots, and regression analysis was used to evaluate anthropometric measures as proxies for total and abdominal fatness.
  
  
  RESULTS
  The percentage of overweight subjects was 41.9%, whereas 55.9% of the subjects were obese, as defined by BMI, and all subjects had a WC exceeding the World Health Organization cut-off point for abdominal obesity. Compared with DXA, the BIA(8) equipment significantly underestimated total %BF (-5.0; -3.6 to -8.5 [mean; 95% confidence interval]), fat mass (-3.6; -3.9 to -3.2), and tr%BF (-8.5; -9.1 to -7.9). The discrepancies between the methods increased with increasing adiposity for both %TBF and tr%BF (both p < 0.001). Variation in BMI explained 28% of the variation in %TBF(DXA) and 51% of %TBF(BIA8). Using WC as a proxy for truncal adiposity, it explained only 18% of tr%BF(DXA) variance and 27% of tr%BF(BIA8) variance. The corresponding figures for truncal fat mass were 49% and 35%, respectively. No significant age effects were observed in any of the regressions.
  
  
  CONCLUSIONS
  BIA(8) underestimated both total and truncal fatness, compared with DXA, with higher dispersion for tr%BF than %TBF. The discrepancies increased with degree of adiposity, suggesting that the accuracy of BIA is negatively affected by obesity.
authors.affiliation: Obesity Unit, m73, Department of Medicine, Karolinska Institute, Karolinska University Hospital, SE-141 86 Stockholm, Sweden. Martin.neovius@ki.se
authors.forename: Martin
authors.initials: M
authors.lastname: Neovius
authors.forename: Erik
authors.initials: E
authors.lastname: Hemmingsson
authors.forename: Bo
authors.initials: B
authors.lastname: Freyschuss
authors.forename: Joanna
authors.initials: J
authors.lastname: Uddén
mesh_terms: D050153:Abdominal Fat / Q000378:metabolism*; D015502:Absorptiometry, Photon / Q000379:methods; D050154:Adiposity / Q000502:physiology*; D000328:Adult; D000368:Aged; D001823:Body Composition / Q000502:physiology; D015992:Body Mass Index; D003430:Cross-Sectional Studies; D017097:Electric Impedance; D005260:Female; D006801:Humans; D008875:Middle Aged; D009765:Obesity / Q000378:metabolism / Q000503:physiopathology*; D015203:Reproducibility of Results; D049629:Waist-Hip Ratio