Maximizing precision and accuracy of the doubly labeled water method via optimal sampling protocol, calculation choices, and incorporation of 17O measurements.

Abstract

BackgroundThe doubly-labeled water (DLW) method is the gold standard methodology for determination of free-living, total daily energy expenditure (TEE). However, there is no single accepted approach for either the sampling protocols (daily vs. two-point, in which samples are collected after dosing and at the end of the measurement period) or the calculations used in the determination of the rate of carbon dioxide production (rCO2) and TEE. Moreover, fluctuations in natural background abundances introduce error in the calculation of rCO2 and TEE. The advent of new technologies makes feasible the possibility of including additional isotope measures (17O) to account for background variation, which may improve accuracy.MethodsSixteen subjects were studied for 7 consecutive days in a whole-room indirect calorimeter (IC) with concurrent measurement of TEE by DLW. Daily urine samples were obtained and isotope ratios determined using off-axis integrated cavity output spectroscopy (OA-ICOS).ResultsWe determined the best combination of approaches for estimating dilution spaces, elimination rates, and calculated average daily carbon dioxide production (VCO2) using six different published equations. Using the best combination, multi-point fitting of isotope elimination rates using the daily urine samples substantially improved the average precision (4.5% vs. 6.0%) and accuracy (−0.5% vs. −3.0%) compared with the two-point method. This improvement may partly reflect the less variable day-to-day chamber measurements of energy expenditure. Utilizing 17O measurements to correct for errors due to background isotope fluctuations provided additional but minor improvements in precision (4.2% vs. 4.5%) and accuracy (0.2% vs. 0.5%).ConclusionsThis work shows that optimizing sampling and calculation protocols can improve the accuracy and precision of DLW measurements.