The various metabolic phases present in critically ill patients have been influential in the development of optimal nutritional treatment due to the complex and fluctuating metabolism that these patients present. Critical illness is characterized by an inflammatory response, which prompts a catabolic response. It can be divided into: early acute phase, where it is observed during the first 48 hours after admission to the ICU, and late acute phase, which does not usually last more than seven days after admission. Likewise, the present study was carried out in order to describe the measured resting energy expenditure (mREE) and feeding practices, during the acute and late phases of critical illness in patients with COVID-19, through an observational study that included to critically ill and mechanically ventilated COVID-19 adult patients. According to their results, both in the acute and late phases, most of the patients were hypermetabolic and fed enterally. In the acute phase, the patients were fed hypocaloric, while in the late phase it was almost normocaloric, according to ESPEN guidelines. Hypermetabolism in both phases along with an increasing loss of urinary nitrogen may indicate that COVID-19 patients remain in a prolonged, acute, catabolic phase. The mREE was performed in the acute and late phase, but it was not corrected by the days of stay in another ICU, which could generate biases.