Abstract
RationaleThe doubly labelled water (DLW) method is the reference method for the estimation of free‐living total energy expenditure (TEE). In this method, where both 2H and 18O are employed, different approaches have been adopted to deal with the non‐conformity observed regarding the distribution space for the labels being non‐coincident with total body water. However, the method adopted can have a significant effect on the estimated TEE.MethodsWe proposed a Bayesian reasoning approach to modify an assumed prior distribution for the space ratio using experimental data to derive the TEE. A Bayesian hierarchical approach was also investigated. The dataset was obtained from 59 adults (37 women) who underwent a DLW experiment during which the 2H and 18O enrichments were measured using isotope ratio mass spectrometry (IRMS).ResultsTEE was estimated at 9925 (9106‐11236) [median and interquartile range], 9646 (9167–10540), and 9,638 (9220–10340) kJ·day−1 for women and at 13961 (12851–15347), 13353 (12651–15088) and 13211 (12653–14238) kJ·day−1 for men, using normalized non‐Bayesian, independent Bayesian and hierarchical Bayesian approaches, respectively. A comparison of hierarchical Bayesian with normalized non‐Bayesian methods indicated a marked difference in behaviour between genders. The median difference was −287 kJ·day−1 for women, and −750 kJ·day−1 for men. In men there is an appreciable compression of the TEE distribution obtained from the hierarchical model compared with the normalized non‐Bayesian methods (range of TEE 11234–15431 kJ·day−1 vs 10786–18221 kJ·day−1). An analogous, yet smaller, compression is seen in women (7081–12287 kJ·day−1 vs 6989–13775 kJ·day−1).ConclusionsThe Bayesian analysis is an appealing method to estimate TEE during DLW experiments. The principal advantages over those obtained using the classical least‐squares method is the generation of potentially more useful estimates of TEE, and improved handling of outliers and missing data scenarios, particularly if a hierarchical model is used.
Highlights
IntroductionAt least three important works describing the principles and practices of the doubly labelled water (DLW) method, striving to promote universal consistency, have been produced, there is still some non‐uniformity in the calculations adopted by workers at different laboratories
The doubly labelled water (DLW) technique of indirect calorimetry for the estimation of total energy expenditure (TEE) was originally suggested by Lifson et al[1] and applied to use in humans someThe main assumptions of the DLW method originally provided by Lifson and McClintock[5] have been more recently summarized and scrutinized by Coward and Cole,[6] who concluded that, whilst none of the six basic assumptions were true, at least the imperfections were manageable.Rapid Commun Mass Spectrom. 2018;32:23–32.wileyonlinelibrary.com/journal/rcm at least three important works describing the principles and practices of the DLW method, striving to promote universal consistency, have been produced, there is still some non‐uniformity in the calculations adopted by workers at different laboratories
The 18O pool size exceeds that of the body water pool, because of the exchange with dissolved CO2 and bicarbonate,[8] which is fundamental to the principle of the DLW method, and because of exchange with bone mineral and other deep pools
Summary
At least three important works describing the principles and practices of the DLW method, striving to promote universal consistency, have been produced, there is still some non‐uniformity in the calculations adopted by workers at different laboratories. This is the case for corrections for fractionation (Assumptions 1 to 3 for space ratios and Assumption 5 are discussed by Coward and Cole[6]). The major difficulty in dealing with fractionation is the estimation of the proportion of water that undergoes phase change (from liquid to vapour) before being lost from the body This is to some extent dependent on the environment of subjects and their physical activity and this needs to be considered within a given experimental paradigm. The practical consequence of this is that neither the accessible 2H nor the 18O volumes of distribution (pools) are coincident with the total body water, and there is a measurable difference between the apparent volumes into which the two isotopes are distributed
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