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.


METHODS
Cross-sectional study.


METHODS
Obesity clinic.


METHODS
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.
Sartorio
A
A
Malattie Metaboliche III e Laboratorio di Endocrinologia Sperimentale, Istituto Auxologico Italiano IRCCS, Piancavallo, Italy.
Malavolti
M
M
Agosti
F
F
Marinone
P G
PG
Caiti
O
O
Battistini
N
N
Bedogni
G
G
D000293:Adolescent; D000328:Adult; D000368:Aged; D000465:Algorithms; D001823:Body Composition / Q000502:physiology*; D015992:Body Mass Index; D001834:Body Water / Q000378:metabolism*; D001835:Body Weight / Q000502:physiology*; D016022:Case-Control Studies; D003430:Cross-Sectional Studies; D017666:Deuterium Oxide; D017097:Electric Impedance; D005110:Extracellular Space / Q000378:metabolism; D005260:Female; D006801:Humans; D008875:Middle Aged; D009765:Obesity / Q000145:classification / Q000378:metabolism; D009767:Obesity, Morbid / Q000145:classification / Q000378:metabolism*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
D017666:Deuterium Oxide