Submitted to: Journal of Federation of American Societies for Experimental Biology
Publication Type: Abstract Only
Publication Acceptance Date: 12/1/2003
Publication Date: 3/24/2004
Citation: Lukaski, H.C., Hall, C.B., Siders, W.A. 2004. Validity of bioelectrical impedance vector analysis (BIVA) to assess fluid change during weight loss [abstract]. The Federation of American Societies for Experimental Biology Journal. 18(4):A1112.
Technical Abstract: Bioelectrical impedance analysis is a safe and convenient method for evaluation of fluid status. Whereas single- and multiple frequency approaches are available to predict fluid volumes, they use empirical models whose theoretical assumptions have been challenged. An alternative is the use of measurements of resistance (R) and reactance (Xc) at 50 kHz, normalized for height (H), plotted as a vector and then compared to norms for a healthy, age- and sex-matched reference population to qualitatively assess hydration status. To date there has been no validation of the quantitative aspects of BIVA. We evaluated the qualitative and quantitative values of BIVA in 30 obese women (BMI > 28 kg/m2) before and monthly during a controlled four month weight loss program. Body weight and total body water (TBW), determined with deuterium dilution, decreased (p<0.0001), and R and Xc increased (p<0.001) during weight loss. The magnitude of the individual vector for each woman determined by the plot of Xc/H vs R/H increased (p<0.001) qualitatively indicating a loss of fluid. We used NHANES III reference impedance data to establish norms for healthy women, calculated Z-scores for each woman serially during weight loss and found that the Z-scores were highly related with the changes in TBW (r = -0.97; p<0.001). These findings show that changes in BIVA accurately reflect changes in body fluid volume and provide the first evidence of validity of BIVA in humans with altered hydration status.