Measurements of Water in Breath and Saliva

The investigators propose to demonstrate the feasibility of measuring 2H:1H and 18O:16O in saliva and breath. The natural abundances of 2H:1H and 18O:16O of urine, saliva, and breath samples will be determined from samples obtained simultaneously from 50 relatively healthy human subjects. We will also measure 2H:1H and 18O:16O enrichments in urine, saliva, and breath of 10 relatively healthy human subjects obtained after consuming a standard DLW dose and compare the estimates of TDEE using these different matrices.