Using Respiratory Gas Analyzers to Determine Resting Metabolic Rate in Adults: A Systematic Review of Validity Studies

Accurate measurement of resting metabolic rate (RMR) is essential for estimating total energy expenditure in both clinical nutrition and sports science. Several methods are available to assess RMR, including predictive equations, isotopic techniques, and indirect calorimetry. In recent years, portable gas analyzers have gained attention as practical and more affordable tools for metabolic assessment. However, their accuracy has not been consistently confirmed, especially across different populations and testing protocols.

This systematic review was conducted in May 2025 following the PRISMA-DTA guidelines. The PubMed, Web of Science, and EBSCO databases were searched for observational studies evaluating the validity of portable gas analyzers for measuring RMR in humans. The methodological quality of the included studies was assessed using the NIH Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies.

Out of 230 identified studies, 16 met the inclusion criteria. The results showed considerable differences in measurement accuracy among devices. Validity was influenced by factors such as the type of device, participant characteristics, and testing methods. Portable analyzers like FitMate and Q-NRG demonstrated good accuracy, while MedGem showed consistent measurement errors, particularly in individuals with higher body fat, leading to an overestimation of RMR.

Overall, the findings highlight the importance of thoroughly validating portable gas analyzers before using them in clinical practice or research. Proper validation is necessary to ensure reliable RMR measurements across different populations and assessment conditions.