AJP - Endocrinology and Metabolism, Vol 263, Issue 6 E1119-E1124, Copyright © 1992 by American Physiological Society
Effect of gender, body composition, and equilibration time on the 2H-to-18O dilution space ratio
M. I. Goran, E. T. Poehlman, K. S. Nair and E. Danforth Jr
Department of Medicine, College of Medicine, University of Vermont, Burlington 05405.
Physiological sources of variation in the 2H-to-18O dilution space ratio
(DSR) were examined in 34 males and 20 females (4-78 yr; 14.7-143.2 kg;
1.8-61.0% body fat). Dilution spaces were obtained by time 0 extrapolation
of isotope washout over 10-14 days, and body composition was obtained by
underwater weight (adults) or bioelectrical impedance (children). The mean
DSR was 1.050 +/- 0.015 (range 1.029-1.111), significantly higher (P <
0.001) than the traditionally assumed value of 1.029 based on exchange over
4 h. Use of the value 1.029 causes a systematic 8% overestimate of energy
expenditure from doubly labeled water, relative to use of the value 1.05.
The DSR was not related to body composition or age but was significantly
higher (P < 0.05) in males (1.052 +/- 0.016) than in females (1.044 +/-
0.012). This gender effect was not explained by differences in the number
of exchangeable hydrogens in the body. We conclude 1) variation in the
2H-to-18O DSR is not explained by body composition but is influenced by the
chemical availability of exchangeable hydrogens to undergo exchange; 2)
because the DSR is not easily predicted, use of the observed dilution
spaces are recommended; 3) if a fixed DSR is used, values of 1.044 and
1.052 are recommended in females and males, respectively.
