December 18, 2025 Author : Mónica Santos (nutrition) Indirect calorimetry is a technique that estimates the body energy expenditure by measuring the amount of oxygen consumed and the amount of carbon dioxide (CO₂) produced during respiration. Since this technique does not directly measure the heat (energy) produced by the body, but rather the gas exchange related to this energy production, it is referred to as indirect. Indirect calorimetry is considered the technique of choice for estimating basal energy needs, as it achieves greater accuracy, especially in severely ill, malnourished, or at-risk individuals. It is approved and recommended by various scientific societies for this purpose. How is indirect calorimetry performed? To perform indirect calorimetry, a mask connected to sensors is used while breathing normally and at rest . The equipment records the amount of oxygen consumed and carbon dioxide produced , which is then used to calculate the respiratory quotient (ratio between carbon dioxide produced and oxygen consumed). From this it is estimated the resting energy expenditure, that is, the energy needs to maintain the body and vital functions, also called the basal metabolic rate. Knowing these individual energy needs, as well as the energy value of various nutrients (carbohydrates, lipids, proteins, for example), the characteristics of the foods that contain them, and other individual needs and goals, it is possible to formulate diets for specific situations. When might indirect calorimetry be indicated? Indirect calorimetry may be indicated in any situation where a personalized nutritional plan is necessary , for example in people: In intensive care with an indication for the start of nutritional support , estimated at 25% of patients admitted to this type of care: Prior to the institution of nutritional support (medical nutritional therapy or oral support); In cases of changes in the patient clinical condition that require alterations in nutritional support. In patients with chronic obstructive pulmonary disease: For respiratory rehabilitation programs; During exacerbation of the disease in inpatient care; During outpatient exacerbation of the disease, when severe weight loss occurs (> 5% in one month or 10% in six months). In patients undergoing surgical treatment for obesity: Prior to surgery; In the sixth postoperative month after significant weight loss has already occurred; Between the 12th and 18th postoperative month, during the weight stabilization phase; When weight gain restarts. In medical and nutritional treatment of refractory obesity In patients with chronic kidney disease requiring dialysis: Prior to renal replacement therapy (e.g., peritoneal dialysis, hemofiltration, and hemodialysis); In the third month after renal replacement therapy; When significant changes in nutritional status and clinical status occur (e.g., infections). In patients with heart failure: With cardiac cachexia; With severe involuntary weight loss (weight loss > 5% in one month or 10% in 6 months). In patients with upper digestive cancer, namely esophageal, gastric, hepatobiliary, and pancreatic cancer: In the initial phase of medical treatment; When there is severe involuntary weight loss (> 5% in one month or 10% in six months); Post-operatively for the initiation of nutritional support (oral or artificial); When significant changes in nutritional status and clinical status occur (e.g., infections). In patients submitted to major surgery, namely cardiothoracic and colorectal surgery In patients with paraplegia in whom it is not possible assess their weight objectively In addition to these disease contexts, there are other situations in which it may be necessary to formulate diets based on individual needs and goals, and where indirect calorimetry may also be indicated, for example: Planning regimens for weight maintenance, gain, or loss ; As part of optimizing energy strategies included in athletes' training plans . Meet the nutrition clinical team from Hospital da Luz network. The content published in the Health Guide is intended for the general public and is provided for informational and educational purposes only. It does not replace individual medical assessment, diagnosis, or personalized clinical advice from a qualified healthcare professional. The content is produced or reviewed by physicians and other healthcare professionals at Hospital da Luz and is based on the knowledge available at the time of publication or the most recent update, as indicated at the beginning of each item.
