Abstract
RationaleVariation in 18O natural abundance can lead to errors in the calculation of total energy expenditure (TEE) when using the doubly labelled water (DLW) method. The use of Bayesian statistics allows a distribution to be assigned to 18O natural abundance, thus allowing a best‐fit value to be used in the calculation. The aim of this study was to calculate within‐subject variation in 18O natural abundance and apply this to our original working model for TEE calculation.MethodsUrine samples from a cohort of 99 women, dosed with 50 g of 20% 2H2O, undertaking a 14‐day breast milk intake protocol, were analysed for 18O. The within‐subject variance was calculated and applied to a Bayesian model for the calculation of TEE in a separate cohort of 36 women. This cohort of 36 women had taken part in a DLW study and had been dosed with 80 mg/kg body weight 2H2O and 150 mg/kg body weight H2 18O.ResultsThe average change in the δ18O value from the 99 women was 1.14‰ (0.77) [0.99, 1.29], with the average within‐subject 18O natural abundance variance being 0.13‰2 (0.25) [0.08, 0.18]. There were no significant differences in TEE (9745 (1414), 9804 (1460) and 9789 (1455) kJ/day, non‐Bayesian, Bluck Bayesian and modified Bayesian models, respectively) between methods.ConclusionsOur findings demonstrate that using a reduced natural variation in 18O as calculated from a population does not impact significantly on the calculation of TEE in our model. It may therefore be more conservative to allow a larger variance to account for individual extremes.
Highlights
The doubly labelled water (DLW) method is considered to be the “gold standard” for measuring free‐living total energy expenditure (TEE) in humans.[1,2] A bolus dose of 2H218O is given and the dilution2122 wileyonlinelibrary.com/journal/rcmRapid Commun Mass Spectrom. 2018;32:2122–2128
This paper looks at calculating TEE using a Bayesian model in the free software WinBUGS.[15]
The aim of the present study was to quantify the natural abundance variation in 18O, and incorporate this into Bayesian modelling to allow a better determination of TEE
Summary
The doubly labelled water (DLW) method is considered to be the “gold standard” for measuring free‐living total energy expenditure (TEE) in humans.[1,2] A bolus dose of 2H218O is given and the dilution2122 wileyonlinelibrary.com/journal/rcmRapid Commun Mass Spectrom. 2018;32:2122–2128. For the DLW method, it is typical to obtain a single pre‐dose sample, which can be plasma, saliva or urine, prior to the experiment, and take this as representative of the natural abundance throughout the measurement period. The underlying assumption of the DLW method is that the natural abundances of both isotopes remain unchanged over the period of measurement. This is a consequence of two of the assumptions of the method; first that water leaves the body unfractionated and secondly that the intake is at the same isotopic enrichment as the body water.[5,6,7] While these assumptions are known to be untrue,[7,8,9] they are generally accepted, as it is not possible to directly measure natural abundance for either isotope during the measurement period. Either the natural abundance must be assumed to be unchanged or indirect methods must be used to overcome the likely variation
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