Energy expenditure by doubly labeled water: validation in humans and proposed calculation

摘要: To further validate the doubly labeled water method for measurement of CO2 production and energy expenditure in humans, we compared it with near-continuous respiratory gas exchange nine healthy young adult males. Subjects were housed a chamber 4 days. Each received 2H2(18)O at either low (n = 6) or moderate 3) isotope dose. Low doses produced initial 2H enrichments 5 10 X 10(-3) atom percent excess, respectively, 18O 2 2.5 10(-2) respectively. Total body was calculated from dilution saliva collected h after by two-point using isotopic urines just before each subject entered left chamber. Isotope relative to predose samples measured ratio mass spectrometry. At dose, overestimated average daily 8 +/- 9% (SD) (range -7 22%). dose difference reduced +4 5% 0-9%). The elimination curves serial one subjects showed expected diurnal variations but otherwise quite smooth. overestimate may be due approximations corrections fractionation dilution. An alternative approach is presented that reduces 1%.