Purpose Metabolic fexibility (MetF), which is a surrogate of metabolic health, can be assessed by the change in the respiratory exchange ratio (RER) in response to an oral glucose tolerance test (OGTT). We aimed to determine the day-to-day
reproducibility of the energy expenditure (EE) and RER response to an OGTT, and whether a simulation-based postcalorimetric correction of metabolic cart readouts improves day-to-day reproducibility.
Methods The EE was assessed (12 young adults, 6 women, 27±2 years old) using an Omnical metabolic cart (Maastricht
Instruments, Maastricht, The Netherlands) after an overnight fast (12 h) and after a 75-g oral glucose dose on 2 separate
days (48 h). On both days, we assessed EE in 7 periods (one 30-min baseline and six 15-min postprandial). The ICcE was
performed immediately after each recording period, and capillary glucose concentration (using a digital glucometer) was
determined.
Results We observed a high day-to-day reproducibility for the assessed RER (coefcients of variation [CV]<4%) and EE
(CVs<9%) in the 7 diferent periods. In contrast, the RER and EE areas under the curve showed a low day-to-day reproducibility (CV=22% and 56%, respectively). Contrary to our expectations, the postcalorimetric correction procedure did
not infuence the day-to-day reproducibility of the energy metabolism response, possibly because the Omnical’s accuracy
was~100%.
Conclusion Our study demonstrates that the energy metabolism response to an OGTT is poorly reproducible (CVs>20%)
even using a very accurate metabolic cart. Furthermore, the postcalorimetric correction procedure did not infuence the
day-to-day reproducibility.
Trial registration NCT04320433; March 25, 2020.Funding for open access charge: Universidad de Granada / CBUA. Supported by the Spanish Ministry of Economy and Competitiveness via Retos de la Sociedad grant DEP2016-79512-R (to JRR), and European Regional Development Funds (ERDF); Spanish Ministry of Education grant (FPU15/04059 to JMAA; and FPU19/01609 to LJ-F); the University of Granada Plan Propio de Investigación 2016-Excellence actions: Unit of Excellence on Exercise and Health (to JRR)—Plan Propio de Investigación 2018 and 2020 Programa Contratos-Puente and Programa Perfeccionamiento de Doctores (to GS-D, and to JMAA respectively); Junta de Andalucía, Consejería de Conocimiento, Investigación y Universidades grant SOMM17/6107/UGR (to JRR) via the ERDF; and the Fundación Alfonso Martín Escudero (to GS-D)
