Reproducibility of the energy metabolism response to an oral glucose tolerance test: influence of a postcalorimetric correction procedure

Abstract

Purpose: Metabolic flexibility (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 (coefficients of variation [CV] < 4%) and EE (CVs < 9%) in the 7 different 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 influence 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 influence the day-to-day reproducibility. Trial registration NCT04320433; March 25, 2020.

Keywords: Glucose tolerance; Indirect calorimetry; Metabolic cart; Postprandial metabolism; Reliability.

Conflict of interest statement

The authors report no conflicts of interest.

© 2022. The Author(s).

Figures

Fig. 1

Study design (replicated on both testing days, 48 h apart). The anthropometry assessments included height and weight. IC: indirect calorimetry (using a metabolic cart) assessments. RMR: resting metabolic rate assessment/period; ICcE: individual calibration control evaluation proposed by Schadewaldt et al. [25]. The bottle icon represents the 75-g oral glucose dose intake. The drop icons represent the capillary blood glucose level assessments. DXA: dual-energy X-ray absorptiometry assessment. Anthropometry and DXA assessments were performed only on day 1. The study protocol timeline is expressed as minutes (min)

Fig. 2

Respiratory exchange ratio (RER, A), energy expenditure (EE, B), and carbohydrate (CHO) utilization (C) with and without applying the individual calibration control evaluation procedure (ICcE), and capillary blood glucose concentrations (D) obtained on Visit 1 and Visit 2 tests. Fasting RMR values correspond to the resting metabolic rate (RMR) period, i.e., before the glucose intake, while 15, 45, 75, 105, 135, and 165 represent the time in minutes for gas exchange data after the glucose intake. The bottle icon (x-axis) represents the moment in which the glucose (75-g dose) was provided. P values from two-factor (Time × ICcE) repeated-measures analysis of variance (ANOVA, n = 12, A-C) for Day 1 and Day 2 comparisons. P values from two-factor (Time × Visit) ANOVA (n = 12, Panel D). Results are presented as mean and standard deviation

Fig. 3

Bland–Altman plots for inter-day reproducibility of the area under the curve for the respiratory exchange ratio (AUC RER; A) and for the energy expenditure (AUC EE; B), with and without applying the individual calibration control evaluation procedure (n = 12). Solid line represents the bias (systematic error) between day 1 and day 2. Dashed lines represent the upper and the lower limits of agreement (mean ± 1.96 standard deviation)