Validity of bioelectrical impedance analysis for measuring changes in body water and percent fat after bariatric surgery.
BACKGROUND
Few studies have validated bioelectrical impedance analysis (BIA) following bariatric surgery.


METHODS
We examined agreement of BIA (Tanita 310) measures of total body water (TBW) and percent body fat (%fat) before (T0) and 12 months (T12) after bariatric surgery, and change between T0 and T12 with reference measures: deuterium oxide dilution for TBW and three-compartment model (3C) for %fat in a subset of participants (n = 50) of the Longitudinal Assessment of Bariatric Surgery-2.


RESULTS
T0 to T12 median (IQR) change in deuterium TBW and 3C %fat was -6.4 L (6.4 L) and -14.8% (13.4%), respectively. There were no statistically significant differences between deuterium and BIA determined TBW [median (IQR) difference: T0 -0.1 L (7.1 L), p = 0.75; T12 0.2 L (5.7 L), p = 0.35; Δ 0.35 L(6.3 L), p = 1.0]. Compared with 3C, BIA underestimated %fat at T0 and T12 [T0 -3.3 (5.6), p < 0.001; T12 -1.7 (5.2), p = 0.04] but not change [0.7 (8.2), p = 0.38]. Except for %fat change, Bland-Altman plots indicated no proportional bias. However, 95% limits of agreement were wide (TBW 15-22 L, %fat 19-20%).


CONCLUSIONS
BIA may be appropriate for evaluating group level response among severely obese adults. However, clinically meaningful differences in the accuracy of BIA between individuals exist.
Institute of Human Nutrition and Department of Epidemiology, Columbia University, New York Obesity Nutrition Research Center, St. Luke's-Roosevelt Hospital, 1111 Amsterdam Avenue, Scrymser Bsmt, New York, NY, 10025, USA, ew2435@columbia.edu.
Elizabeth M
EM
Widen
Gladys
G
Strain
Wendy C
WC
King
Wenwen
W
Yu
Susan
S
Lin
Bret
B
Goodpaster
John
J
Thornton
Anita
A
Courcoulas
Alfons
A
Pomp
Dympna
D
Gallagher
D000273:Adipose Tissue; D000328:Adult; D050110:Bariatric Surgery; D001823:Body Composition / Q000502:physiology*; D001834:Body Water; D017097:Electric Impedance; D005260:Female; D006801:Humans; D007201:Indicator Dilution Techniques; D008297:Male; D011184:Postoperative Period