Both over- and underfeeding hospitalized patients can have detrimental impacts. Around 33% of hospitalized patients (non-maternal, non-neonatal) have malnutrition, with half of these patients experiencing a worsening of malnutrition severity during their admission. Malnutrition has a significant negative impact on overall patient morbidity, mortality, and quality of life, as well as increased healthcare costs. Predictive equations are the most widely used means to assessing energy needs, yet the equations often lead to under- and overfeeding. Indirect calorimetry (IC) is considered the gold standard for assessing energy needs in hospitalized children and adults; however, most hospitals do not have access to the equipment necessary to perform IC evaluations. This session will review the evidence comparing estimated energy needs from predictive equations and measured resting energy expenditure from indirect calorimetry. It will also review the indicators for testing both pediatric and adult patients. A case study will also be reviewed which will demonstrate how important the use of IC is for adequately feeding critically ill patients and how optimal nutrition can optimize recovery.