Preexisting malnutrition in the ICU

PURPOSE OF REVIEW: Preexisting malnutrition - defined as malnutrition present at the time of ICU admission - represents a critical determinant of outcomes in intensive care. This review summarizes recent evidence regarding its diagnosis, prevalence, clinical significance and nutritional therapy, emphasizing the role of the Global Leadership Initiative on Malnutrition (GLIM) framework. RECENT FINDINGS: Recent studies applying the GLIM criteria within 24-72 h of ICU admission report malnutrition prevalence ranging from 38 to 68%. Distinguishing preexisting malnutrition from "nutritional risk" is essential, as the former denotes an established nutrient and protein deficit prior to the onset of critical illness. Advances in muscle-mass assessment using various methods have refined phenotypic evaluation. Preexisting malnutrition is consistently associated with prolonged ICU stay, higher infection rates and delayed rehabilitation. While preexisting malnutrition may not markedly influence very short-term outcomes such as 7-day mortality, its influence extends beyond the acute phase, impacting medium-term and long-term trajectories through organ dysfunction, infection risk, persistent muscle wasting and impaired rehabilitation potential. Current evidence does not support early full feeding during the acute phase even in the preexisting malnutrition patients, but highlights the need for sustained, individualized nutritional rehabilitation after ICU discharge and beyond. SUMMARY: Preexisting malnutrition is common and clinically impactful among critically ill adults. Incorporating standardized GLIM-based diagnosis into ICU practice enables earlier recognition and tailored nutritional strategies across the continuum of critical care and recovery.