Lean mass loss in the intensive care unit and its restoration: A narrative review

The preservation of lean mass (LM) and its restoration following catabolic loss represents a primary challenge for clinical nutrition in critically ill patients. A comprehensive review of recent literature confirms a clinical dilemma between unresponsiveness for feeding and harm of overfeeding and underfeeding. Time point-specific assessment and monitoring of body composition-via computed tomography, bioelectrical impedance analysis (BIA), and ultrasound-are recommended to become an integral part of daily care for all intensive care unit (ICU) patients. Currently, serial BIA for measuring fat-free mass appears to be the most feasible and promising method. Energy and protein supply throughout the phases of critical illness should be guided by sex-specific fat-free mass rather than total body weight, reinforcing the value of indirect calorimetry. Given the prevalence of post-intensive care syndrome, nutrition therapy and monitoring must continue into the post-ICU period. Combined strategies-rather than isolated interventions-provide the most plausible framework to support LM recovery during ICU care and throughout post-ICU rehabilitation. Future approaches, supported by machine learning, will warrant the combined use of biomarkers and clinical variables to identify anabolic resistance and determine "readiness for feeding." Further research is needed to elucidate the effects of micronutrient supplementation, ketogenic diets, and ω-3 fatty acids on muscle tissue, with a focus on mitochondrial function and anti-inflammation. The potential of orexigenic (eg, ghrelin) and anabolic (eg, nandrolone) hormones in the post-ICU phase warrants further investigation.