Concepts of indirect calorimetry on metabolic disorders: a narrative review

Introduction: Indirect calorimetry remains a gold standard in measuring resting energy expenditure in the clinical field. Through its measurements, it is possible to offers a patient’s energy needs to maximize nutritional therapy benefits. However, the concepts and methodological basis of collected data can be difficult to be interpreted by users in clinical practice. Objective: To address the concepts of total daily energy expenditure and its components and present the methodological aspects of indirect calorimetry that can guide the clinical field. Method: Narrative bibliographic review using the electronic Pubmed (US National Library of Medicine), SCOPUS, and Scientific Electronic Library Online (SCIELO) databases. The research was carried out in the period between 1905-2019, using the following identifiers in Health Sciences Descriptors: Basal Metabolism, Energy Metabolism and Indirect Calorimetry. We selected 55 researches published that presented contents related to the objectives of this study. Result: The total daily energy expenditure (TDEE) is comprised of three main components, such as physical activity (PA), thermic effect of food (TEF) and basal metabolic rate (BMR) and/or resting energy expenditure (REE). The REE is generally evaluated by indirect calorimetry, which also provides information on the respiratory coefficient (RQ) or oxidation of substrates. Its result varies depending on the existence of some metabolic disorders such as obesity or malnutrition. Therefore, the proper management of the methodological aspects of indirect calorimetry and its subsequent interpretation in metabolic disorders is essential to guarantee the results’ quality. Conclusion: Energy expenditure concepts and the methodological basis of indirect calorimetry are relevant to providing individualized attention to patients with metabolic disorders. This review can be used as a practical guide, helping to understand the correct application of the indirect calorimetry technique in studies related to energy expenditure with an emphasis on metabolic disorders.