Body water distribution in severe obesity and its assessment from eight-polar bioelectrical impedance analysis

Eur J Clin Nutr. 2005 Feb;59(2):155-60. doi: 10.1038/sj.ejcn.1602049.


Objective: 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.

Design: Cross-sectional study.

Setting: Obesity clinic.

Subjects: 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).

Methods: 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).

Results: 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.

Conclusions: 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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Algorithms
  • Body Composition / physiology*
  • Body Mass Index
  • Body Water / metabolism*
  • Body Weight / physiology*
  • Case-Control Studies
  • Cross-Sectional Studies
  • Deuterium Oxide
  • Electric Impedance*
  • Extracellular Space / metabolism
  • Female
  • Humans
  • Middle Aged
  • Obesity / classification
  • Obesity / metabolism
  • Obesity, Morbid / classification
  • Obesity, Morbid / metabolism*
  • Reproducibility of Results
  • Sensitivity and Specificity


  • Deuterium Oxide