Total body water estimations in healthy men and women using bioimpedance spectroscopy: a deuterium oxide comparison

Background: Total body water (TBW) estimations have been used to estimate body composition, particularly fat-free mass, to aid in nutritional interventions, and to monitor hydration status. In the past, bioimpedance spectroscopy (BIS) devices have been used to estimate TBW. Previous investigations have examined the validity of the XiTRON 4000B (XiTRON Technologies) BIS device for estimating TBW. Recently, a new BIS device (Imp (TM) SFB7) has become available, claiming greater precision when estimating TBW. The Imp T SFB7 (SFB7) is based on similar BIS principles, while offering increased portability and a greater range of frequencies when compared to older devices, such as the XiTRON 4000B (4000B). The purpose of this study was to examine the validity of the SFB7 for estimating total body water in healthy college-age men and women compared to the 4000B and deuterium oxide (D2O). Methods: Twenty-eight Caucasian men and women (14 men, 14 women; 24 +/- 4 yrs; 174.6 +/- 8.7 cm; 72.80 +/- 17.58 kg) had their TBW estimated by the SFB7, the 4000B, and D2O. Results: Both BIS devices produced similar standard error of estimate (SEE) and r values (SFB7, SEE = 2.12L, r = 0.98; 4000B, SEE = 2.99L, r = 0.96) when compared to D2O, though a significant constant error (CE) was detected for the 4000B (2.26L, p <= 0.025). The 4000B produced a larger total error (TE) and CE (TE = 3.81L, CE = 2.26L) when compared to the SFB7 (TE = 2.21L, CE = -0.09L). Additionally, the limits of agreement were larger for the 4000B (-3.88 to 8.39L) than the SFB7 (-4.50 to 4.31L). These results were consistent when sex was analyzed separately, though women produced lower SEE and TE values for both devices. Conclusion: The 4000B and SFB7 are valid BIS devices when compared to D2O to estimate TBW in college-age Caucasian men and women. Furthermore, the new SFB7 device displayed greater precision in comparison to the 4000B, which may decrease the error when estimating TBW on an individual basis.