Human Evolutionary Biology, Harvard University, Cambridge, MA, USA.
Department of Geosciences, Boise State University, Boise, ID, USA.
J Nutr. 2022 Jan 11;152(1):78-85. doi: 10.1093/jn/nxab324.
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.
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.
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.
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.
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.
鉴于双标水（DLW）方法在确定能量消耗方面的实用性，人们欢迎对样品进行同位素分析的其他技术。基于激光的仪器就是这样一种新的分析工具，但它们在 DLW 研究中的准确性和可行性还没有得到充分研究。
我们评估了激光同位素比测量作为 DLW 方法的一部分，用于估计二氧化碳生成率（rCO2）和总能量消耗（TEE）的准确性，这是在组间比较研究设计中进行的。
使用基于激光的仪器[偏轴集成腔输出光谱（OA-ICOS）]分析来自先前研究的尿液样本。在该研究中，参与者在 20 周内摄入高、中或低碳水化合物饮食；在 2H 和 18O 富集水剂量前后的第 18-20 周获得尿液样本。通过标准方法计算的同位素比（δ2H 和 δ18O）、rCO2 和 TEE 与以前用同位素比质谱（IRMS）的标准技术获得的结果进行了比较。计算了 IRMS 和 OA-ICOS 之间的偏差、SD 和偏差±1.96SD 带。
尽管在高富集水平下测量的 δ18O 值存在差异，但 OA-ICOS 和 IRMS 的 rCO2 和 TEE 趋势是等效的（分别在 1.2%和 4.1%以内）。随着 18O 富集的增加，OA-ICOS 的 δ18O 值显示出与 IRMS 结果的递增偏移（在 18O 富集最高的时间点，平均±2‰偏移 4.6-5.7‰），而氢同位素比（δ2H）在两种方法之间仅略有差异（所有时间点的平均偏移-4.9‰）。在以前的研究中，使用较小的参与者子集和时间点重现了不同饮食之间的 TEE 差异。
OA-ICOS 分析是 DLW 方法的一种准确且可行的技术。鉴于在高富集时观察到的 δ18O 偏移，建议对每个 OA-ICOS 仪器设置与既定方法（例如 IRMS）进行验证。
