Abstract
Head and neck cancer represents one of the most nutritionally vulnerable oncologic populations, driven by tumor-related functional impairment, treatment toxicities, and complex metabolic alterations. Malnutrition and skeletal muscle loss are highly prevalent at diagnosis and frequently worsen during therapy, impairing treatment tolerance, functional status, and clinical outcomes. This narrative review synthesizes clinical and mechanistic evidence on the interrelated roles of malnutrition, low skeletal muscle mass, mucosal toxicity, and systemic inflammation across the perioperative, definitive treatment, and post-acute recovery phases. Particular emphasis is placed on the limitations of body mass index-based assessment and the importance of integrating validated screening tools with context-appropriate phenotypic evaluation of muscle depletion. Beyond conventional energy replacement, we examine the evidence supporting perioperative immunonutrition, discuss the contextual limitations of immune-modulating strategies during chemoradiotherapy, and consider emerging adjunctive metabolic approaches. Mucositis is conceptualized not only as a local toxicity but also as a contributor to reduced intake and inflammation-driven catabolism. The post-treatment phase is highlighted as a critical period for continued monitoring of body composition and functional recovery. Collectively, the available evidence supports a shift from weight-centered nutritional paradigms toward an integrated, body composition-oriented and inflammation-aware framework for supportive care in head and neck oncology.