Malnutrition in Maintenance Dialysis: From Metabolic Disorder to Multisystem Complications

Malnutrition and protein-energy wasting (PEW) are closely related yet distinct clinical entities. While malnutrition broadly refers to nutritional deficits arising primarily from inadequate dietary intake, PEW is a complex syndrome specific to chronic kidney disease characterized by the progressive loss of body protein mass and energy reserves driven by systemic hypercatabolism, uremic toxicity, chronic inflammation that cannot be corrected by dietary intake alone. Nutritional impairment remains one of the most prevalent and clinically significant complications of end-stage kidney disease (ESKD), affecting a substantial proportion of patients receiving maintenance hemodialysis and peritoneal dialysis despite advances in dialysis technology and multidisciplinary care. Traditionally, nutritional impairment in dialysis was evaluated through isolated surrogate markers such as serum albumin or body weight. However, these conventional measures capture only a fraction of the underlying biological complexity and are heavily confounded by non-nutritional factors, including systemic inflammation and volume overload. Recognizing the intertwined contributions of uremic milieu, inflammation, oxidative stress, and hypercatabolism led to a paradigm shift toward composite nutritional assessment tools, most notably the Malnutrition–Inflammation Score (MIS), which integrates dietary, anthropometric, clinical, and biochemical parameters to comprehensively quantify PEW severity and systemic risk. Current evidence supports a broader conceptual framework in which nutritional status is recognized as an important clinical correlate and potential contributor to metabolic health and multisystem complications, including immune dysfunction, cardiovascular disease, frailty, hospitalization, and all-cause mortality. Consequently, nutritional impairment in dialysis should be viewed as a multifactorial clinical condition requiring comprehensive, multi-domain assessment rather than reliance on isolated biomarkers. This review examines the systemic consequences of malnutrition and PEW in maintenance dialysis patients, highlighting emerging evidence linking nutritional deficits with host immune impairment, cardiovascular disease, and adverse clinical outcomes.