Total energy expenditure assessed by salivary doubly labelled water analysis and its relevance for short-term energy balance in humans.

RationaleThe doubly labelled water (DLW) method is a stable isotopic technique for measuring total energy expenditure (TEE). Saliva is the easiest sampling fluid for assessing isotopic enrichments, but blood is considered superior because of its rapid exchange with body water. Therefore, we compared a large range of isotopic enrichments in saliva and blood, and related TEE in subjects with their ad libitum total energy intake (TEI). The relevance of these parameters to body weight and fat change over an 8-day interval was also assessed. MethodsThirty subjects underwent DLW analysis over either 8 or 14days, during which time initial and final blood and saliva enrichments were compared. TEI was assessed by dieticians over the 8-day period only. Isotope ratio mass spectrometry was used for the measurement of H-2 and O-18 values. ResultsNo discrepancies were observed between sampling fluids over a wide range of enrichments. During the 8-day period, average TEI exceeded TEE by similar to 5% or less. Using saliva as sampling fluid, TEI and TEI-TEE, but not TEE, were positively correlated to body weight change. TEI-TEE and physical activity EE (AEE), but not TEI, correlated, respectively, positively and negatively to changes in fat mass. ConclusionsThe DLW method in humans can be reliably applied using saliva as sampling fluid. TEI-TEE as well as AEE contributes significantly to changes in fat mass over an 8-day period. Copyright (c) 2015 John Wiley & Sons, Ltd.