Effect of gender, body composition, and equilibration time on the 2H-to-18O dilution space ratio.
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.
Goran
M I
MI
Department of Medicine, College of Medicine, University of Vermont, Burlington 05405.
Poehlman
E T
ET
Nair
K S
KS
Danforth
E
E
D000273:Adipose Tissue / Q000033:anatomy & histology / Q000473:pathology; D000293:Adolescent; D000328:Adult; D000368:Aged; D001823:Body Composition; D001834:Body Water / Q000378:metabolism*; D002648:Child; D002675:Child, Preschool; D003903:Deuterium; D005260:Female; D006801:Humans; D007201:Indicator Dilution Techniques; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D009765:Obesity / Q000378:metabolism / Q000473:pathology; D010103:Oxygen Isotopes; D012727:Sex Characteristics; D013997:Time Factors
D010103:Oxygen Isotopes; D003903:Deuterium