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


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/m2 (ie not obese), 25 with BMI between 30.0 and 39.9 kg/m2 (ie class I and II obese), and 25 with BMI between 40.0 and 48.2 kg/m2 (ie class III obese).

Methods: TBW and ECW were measured by 2H2O 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 (RIx) was calculated as height 2/Rx.

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, RI500 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, RI5 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/m2. Eight-polar BIA offers accurate estimates of TBW and ECW in women with a wide range of BMI (19.1–48.2 kg/m2) without the need of population-specific formulae.

Sponsorship: Progetti di Ricerca Corrente, Istituto Auxologico Italiano.

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Correspondence to G Bedogni.

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Guarantors: A Sartorio and G Bedogni.

Contributors: AS coordinated the study and contributed to the final version of the manuscript; GB analyzed the data and wrote the first draft of the manuscript; MM, OC and NB performed laboratory measurements; FA and PG Marinone performed clinical measurements.

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Sartorio, A., Malavolti, M., Agosti, F. et al. Body water distribution in severe obesity and its assessment from eight-polar bioelectrical impedance analysis. Eur J Clin Nutr 59, 155–160 (2005).

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  • obesity
  • total body water
  • extracellular water
  • bioelectrical impedance analysis

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