Metabolic flexibility, a surrogate for metabolic health, can be measured using the variation in the respiratory exchange ratio (RER) in response to an oral glucose tolerance test (OGTT). The Omnical metabolic cart was used to measure energy expenditure (EE) and RER response to an OGTT. The day-to-day reproducibility of these measures was assessed, next to the utility of a post calorimetric correction procedure. Read more on the study “Reproducibility of the energy metabolism response to an oral glucose tolerance test: influence of a post calorimetric correction procedure” by Alcantara et al (2022).  


To learn more about human energy balance, the indirect calorimetry (IC) technique is frequently used to measure whole-body energy metabolism. Today, IC is a flexible instrument with many applications that is frequently used to assess the impact of nutrients (such as metabolic flexibility), medications, bioactive substances, etc. on thermogenesis and fuel oxidation metabolism. As previously indicated, the ability to adjust fuel oxidation to fuel availability and energy demand is known as metabolic flexibility (MetF), and it may be evaluated using in vivo data (IC). MetF is frequently used as a proxy for metabolic health when viewed from the perspective of the entire body. It has been proposed that an impaired MetF is linked to an increased risk of body weight gain and metabolic diseases. MetF is related to energy balance and energy intake management.

Nowadays, the euglycemic-hyperinsulinemic clamp is the method most frequently employed to evaluate MetF. However, the application of this approach in epidemiologic or large-cohort research is often not feasible. As a result, the use of alternate procedures like the oral glucose tolerance test (OGTT), which uses simpler laboratory assays and protocols, is growing. A metabolic cart can be used to quantify postprandial oxygen consumption (VO2) and carbon dioxide production (VCO2) and estimate the respiratory exchange ratio (RER) while evaluating MetF using an OGTT. The increase in RER during an OGTT is then frequently used to calculate MetF. Unfortunately, a lot of metabolic carts have demonstrated poor daily repeatability and limited precision. That might negatively affect gas exchange measures, making it impossible to determine RER changes accurately during the postprandial gas exchange assessment. Schadewaldt et al. developed a method to correct the metabolic cart readouts utilizing controlled pure nitrogen (N2) and carbon dioxide (CO2) simultaneous gas infusions in order to improve the accuracy and daily reproducibility of the metabolic carts (hereinafter individual calibration control evaluation [ICcE]).

In short, the ICcE is performed to replicate VO2 and VCO2 rates after the participant’s gas exchange recording in order to determine the metabolic cart error. After two consecutive OGTTs (ingested three hours apart), this error was used to correct the participant’s indirect calorimetry readouts using the ICcE procedure. It was found that the “corrected” data’s RER pattern more accurately reflected the anticipated physiological response than the “uncorrected” metabolic cart data. They therefore proposed that the use of the ICcE technique might enhance the postprandial evaluations. Therefore, even if it hasn’t been tried yet, it is feasible that the ICcE technique increases the daily repeatability of postprandial gas exchange (i.e., raises the RER reproducibility).

Goal of this study

Metabolic flexibility (MetF), a surrogate for metabolic health, can be measured using the variation in the respiratory exchange ratio (RER) in response to an oral glucose tolerance test (OGTT). The goal of the study was to determine if metabolic cart readouts of energy expenditure (EE) and RER response to an OGTT had better day-to-day reproducibility when corrected for post calorimetric simulation-based errors.

In this investigation, two non-consecutive (48-h apart) tests were used to assess the daily repeatability of gas exchange before and after an OGTT in young healthy adults. Additionally, we sought to ascertain whether the ICcE suggested by Schadewaldt et al. has an impact on the daily repeatability of the measured gas exchange parameters.


In this study, 12 young adults (6 men and 6 women) took part. The requirements for inclusion were: (i) being over the age of 18; (ii) having a body mass index (BMI) of 18.5 to 27.5 kg/m2 (inclusive); and (iii) maintaining a constant body weight during the previous three months (i.e., changes)

Study design

Using the Omnical metabolic cart system, gas exchange was evaluated during a 12-hour fast (referred to as the resting metabolic rate [RMR] phase) and following a 75-g oral glucose dosage (NUTER TEC: orange taste, Toulouse, France) (Maastricht Instruments, Maastricht, The Netherlands). The tests began in the morning (about 9 am) on two separate, non-consecutive days that were 48 hours apart. The Omnical system was outfitted with a plastic canopy-hood in order to collect the participant’s gas exchange. Notably, on each testing day and before the gas exchange measurement, the flow and gas analyzers of the Omnical system were automatically calibrated in accordance with the manufacturer’s instructions.


Participants drove themselves to the research facility, forgoing any recent moderate to vigorous physical activity. Participants also skipped the previous 48 and 24 hours of vigorous and moderately intense physical exercise, respectively. The 12-hour fasting period was met by the participants on the testing day by confirming that they had eaten the standardized 24-hour ad-libitum meal plan, including dinner, 12 hours before to the commencement of the baseline assessment (i.e., the RMR period). Participants were told to pick and choose one of the two possibilities (i.e., the menu was not exchangeable). To duplicate food intake, participants had to record how much they ate in a food diary prior to the first visit. Additionally, participants abstained from using any stimulant medicines or beverages (such coffee and tea) that could affect metabolism during the previous 24 hours.

Before the RMR period, participants did not move for 20 minutes while lying immobile on a bed that had been reclined. Additionally, participants were instructed to spend 10 minutes lying on the bed before to each postprandial gas exchange measurement. During the gas exchange measurements, participants were encouraged to breathe regularly and refrain from dozing off, talking, or fidgeting. All tests were conducted in the same calm, low-light environment with controlled ambient temperature and humidity. Participants received an oral glucose drink and had two minutes to consume it. To test the precision of the metabolic cart, the researchers ran regular methanol burns and regulated N2 and CO2 pure gas infusions every week (the trial lasted a total of 9 weeks).

Routine accuracy checks for metabolic carts

The researchers conducted methanol burning and pure gas infusions tests in order to make sure that the metabolic cart’s performance was ideal for its intended usage. These tests were done every week (9 weeks in total) and before the first testing day. According to the manufacturer’s instructions, daily calibrations of the flow sensor and gases analyzer were carried out.


The study demonstrates that, despite using an accurate metabolic cart for the gas exchange measurement, the postprandial gas exchange parameters (AUC RER, AUC EE) determined after two non-consecutive (48-h apart) OGTT are poorly reproducible, as shown by the observed AUCs CV (> 20%). Furthermore, since the values of the uncorrected and corrected gas exchange parameters were comparable, we did not notice any effect of the ICcE technique on the daily reproducibility. Our research suggests that using the Omnical metabolic cart does not require the ICcE technique.

Related products

Omnical RMR

The Omnical is the most versatile and accurate indirect calorimeter for research purposes on the market. Comprised of state-of-the-art technology using the highest-class precision measurement instruments, it enables customers to perform studies in various research fields. The system is designed to measure energy metabolism ranging from resting metabolism rate (RMR) to sports performance testing (e.g. VO2max tests) with high accuracy.


The methanol combustion kit contains a specifically designed burner, able to fit on a standard methanol bottle and a fire safety bucket. The burn rate of this setup is designed to match the RMR of adult person.

The gas infusion kit in specifically designed to test the dynamic response of a room calorimeter system. It allows the researcher to connection of the gas of choice by (CO2, N2, mixture) and up to three different infusion rates can be set. In the software included an infusion pattern can be set and after starting, the software executes the set pattern and logs the weight coming from the precision scale (not included).

How can we help you with your research?

Maastricht Instruments creates equipment in the field for indirect calorimetry measurements. We provide support for studies, research and measurements alongside our indirect calorimetry products. Consult us about our indirect calorimetry metabolic  cart,  whole room calorimeter  systems or  accelerometry  add-ons. Please  contact us or find more information on our information pages.


Alcantara JMA, Sanchez-Delgado G, Jurado-Fasoli L, Galgani JE, Labayen I, Ruiz JR. Reproducibility of the energy metabolism response to an oral glucose tolerance test: influence of a postcalorimetric correction procedure. Eur J Nutr. 2022 Aug 25. doi: 10.1007/s00394-022-02986-w. Epub ahead of print. PMID: 36006468.