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Abstract
To measure body water distribution and to evaluate the accuracy of eight-polar bioelectrical impedance analysis (BIA) for the assessment of total body water (TBW) and extracellular water (ECW) in severe obesity. Cross-sectional study. Obesity clinic. In all, 75 women aged 18-66 y, 25 with body mass index (BMI) between 19.1 and 29.9 kg/m(2) (ie not obese), 25 with BMI between 30.0 and 39.9 kg/m(2) (ie class I and II obese), and 25 with BMI between 40.0 and 48.2 kg/m(2) (ie class III obese). TBW and ECW were measured by (2)H(2)O and Br dilution. Body resistance (R) was obtained by summing the resistances of arms, trunk and legs as measured by eight-polar BIA (InBody 3.0, Biospace, Seoul, Korea). The resistance index at a frequency of x kHz (RI(x)) was calculated as height (2)/R(x). ECW : TBW was similar in women with class III (46+/-3%, mean+/-s.d.) and class I-II obesity (45+/-3%) but higher than in nonobese women (39+/-3%, P<0.05). In a random subsample of 37 subjects, RI(500) explained 82% of TBW variance (P<0.0001) and cross-validation of the obtained algorithm in the remaining 38 subjects gave a percent root mean square error (RMSE%) of 5% and a pure error (PE) of 2.1 l. In the same subjects, RI(5) explained 87% of ECW variance (P<0.0001) and cross-validation of the obtained algorithm gave a RMSE% of 8% and a PE of 1.4 l. The contribution of weight and BMI to the prediction of TBW and ECW was nil or negligible on practical grounds. ECW : TBW is similar in women with class I-II and class III obesity up to BMI values of 48.2 kg/m(2). Eight-polar BIA offers accurate estimates of TBW and ECW in women with a wide range of BMI (19.1-48.2 kg/m(2)) without the need of population-specific formulae.
Highlights
As compared to normal-weight women, obese women have a lower total body water (TBW) per unit of weight (Wt) and a higher extracellular water (ECW) per unit of TBW (Waki et al, 1991)
TBW was significantly higher in obese than in nonobese women but there was no difference in TBW between class I–II and class III obesity
We found no difference in ECW : TBW between class III and class I–II obesity even if obese women had an expanded ECW : TBW as compared to nonobese women
Summary
As compared to normal-weight women, obese women have a lower total body water (TBW) per unit of weight (Wt) and a higher extracellular water (ECW) per unit of TBW (Waki et al, 1991). Most of the data on body water distribution of obese subjects were obtained in women with class I or II obesity and less data are available for women with class III obesity. The altered body water distribution of obese women has implications for the assessment of body composition from bioelectrical impedance analysis (BIA) (Deurenberg, 1996; Steijaert et al, 1997). The aim of this study was twofold: (1) to establish whether ECW : TBW differs in class III obesity vs class I–II obesity, and (2) to evaluate the accuracy of eight-polar BIA in the assessment of TBW and ECW in obese women
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