Accuracy and Practical Considerations for Doubly Labeled Water Analysis in Nutrition Studies Using a Laser-Based Isotope Instrument (Off-Axis Integrated Cavity Output Spectroscopy)

Authors

Linda M. Reynard, Boise State UniversityFollow
William W. Wong, Baylor College of Medicine
Noreen Tuross, Harvard University

Document Type

Article

Publication Date

1-2022

Abstract

Background: Given the utility of the doubly labeled water (DLW) method for determination of energy expenditure, additional techniques for isotope analysis of the samples are welcome. Laser-based instruments are one such new analytical tool, but their accuracy and feasibility for DLW studies are grossly understudied.

Objectives: We assessed the accuracy of laser-based isotope ratio measurements as part of the DLW method for estimation of carbon dioxide production rate (rCO₂) and total energy expenditure (TEE), in between-group comparison study designs.

Methods: Urine samples from a previous study were analyzed with a laser-based instrument [off-axis integrated cavity output spectroscopy (OA-ICOS)]. In that study, participants consumed a high-, moderate-, or low-carbohydrate diet for 20 wk; urine samples were obtained in weeks 18–20 before and after a ²H- and ¹⁸O-enriched water dose. Isotope ratios (δ²H and δ¹⁸O), rCO₂, and TEE calculated by standard methods were compared to results previously obtained with the standard technique of isotope ratio mass spectrometry (IRMS). Bias, SD, and bias ± 1.96SD bands between IRMS and OA-ICOS were computed.

Results: The between OA-ICOS and IRMS rCO₂ and TEE trends were equivalent (within 1.2% and 4.1%, respectively), in spite of the differences in measured δ¹⁸O values at high enrichment levels. The OA-ICOS δ¹⁸O values displayed an increasing offset from the IRMS results as the ¹⁸O enrichment increased (mean ± SD 4.6–5.7‰ ± 2‰ offset at the time point with highest ¹⁸O enrichment, ∼135‰), whereas the hydrogen isotope ratio (δ²H) differed only slightly between the methods (mean offset −4.9‰ for all time points). The between-diet differences in TEE from the previous study were recapitulated with a smaller subset of participants and time points.

Conclusions: OA-ICOS analysis is an accurate and feasible technique for the DLW method. Given the δ¹⁸O offset observed at high enrichment, validation of each OA-ICOS instrumental setup against established methods (e.g., IRMS) is recommended.

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Publication Information

Reynard, Linda M.; Wong, William W.; and Tuross, Noreen. (2022). "Accuracy and Practical Considerations for Doubly Labeled Water Analysis in Nutrition Studies Using a Laser-Based Isotope Instrument (Off-Axis Integrated Cavity Output Spectroscopy)". The Journal of Nutrition, 152(1), 78-85. https://doi.org/10.1093/jn/nxab324