Objective: This umbrella review investigates the influence of immunonutrition on postoperative outcomes in patients undergoing surgical treatment for head and neck cancer. The primary focus is to determine whether supplementation with immunomodulatory nutrients enhances recovery, reduces surgical complications, and shortens hospital stay durations. Method: Systematic reviews of randomized controlled trials were analyzed, sourced from prominent databases including PubMed, Web of Science, Scopus, and Cochrane Library. Searches employed MeSH terms targeting immunonutrition and surgical procedures in head and neck oncology. Two independent reviewers conducted the selection and extraction of relevant studies, resolving discrepancies through consensus. Methodological rigor was evaluated using AMSTAR 2 and ROBIS tools, and the certainty of evidence was graded via the GRADE framework. Statistical assessments utilized Bayesian modeling to estimate pooled effects and evaluate heterogeneity. Results: The analysis encompassed ten high-quality reviews comparing immunonutrition interventions to standard perioperative care. Findings demonstrated a modest but significant reduction in hospital stay duration (effect size: 0.18; 95% CI: 0.02–0.35), suggesting a potential benefit of immunonutrition. Nonetheless, considerable variability in supplementation regimens and reported outcomes across studies underscores the need for protocol standardization and consistent reporting. Conclusion: Immunonutrition emerges as a valuable strategy in optimizing postoperative care for head and neck cancer patients, with evidence pointing to reduced hospitalization times and improved recovery trajectories. However, more robust and harmonized research is required to establish comprehensive guidelines and confirm these preliminary findings.