Calorimetry in obese women: comparison of two different operating indirect calorimeters together with the predictive equation of Harris and Benedict

In patients with obesity, it is important to know the exact metabolic function in order to assess balanced nutritional support, reducing the risks of the initial situation. For an adequate detection of the resting metabolic rate (RMR), commonly indirect calorimeters are used. In the present study, two different indirect calorimeters [an expiratory collection open-circuit system (Fitmate) and a ventilated open-circuit system (Quark RMR)], were correlated and analysed for better adequacy. The predictive equation of Harris–Benedict (HBE) was confronted with the measured RMR of the better evaluated indirect calorimeter. 42 obese women (age 55 ± 12 years and BMI 42.9 ± 6.8 kg/m²) were included in the study after selecting patients according to the predefined inclusion and exclusion criteria. Measurement durations of each 15 min were performed after an overnight fast with both calorimeters. Received values of Fitmate and Quark were compared while the calorimeter with the more reliable values was compared with the HBE. Significant correlations (P < 0.001) between the devices were achieved, although a significant difference of 1,051 kJ/day (14.9%) between Fitmate (7,542 ± 1,230 kJ/day) and Quark RMR (6,491 ± 806 kJ/day) was detected. The mean calculated RMR of the HBE (7,181 ± 716 kJ/day), in comparison with Quark RMR was significantly different (P < 0.001). The correlation of the two indirect calorimeters, their different functioning, led to significant differences between devices and RMR measurements. The HBE was found to overestimate the measured RMR of Quark RMR. Though the HBE was developed on lean subject, it cannot be considered as a reliable equation for obese subjects.