Patients with schizophrenia receiving long-term antipsychotic therapy are at increased risk of chronic low-grade inflammation and metabolic disturbances, which contribute to poor physical health outcomes and increased cardiovascular morbidity. Structured Medical Nutrition Therapy (MNT), consisting of individualized nutrition assessment, dietary intervention, nutrition education, and regular monitoring, has the potential to improve dietary quality and modulate systemic inflammation. This study aims to evaluate the effect of Structured Medical Nutrition Therapy on the Systemic Inflammation Index (SII), a novel inflammatory biomarker derived from neutrophil, lymphocyte, and platelet counts, in patients with schizophrenia receiving antipsychotic therapy. It is hypothesized that patients receiving structured MNT will demonstrate a greater reduction in SII compared with those receiving standard nutritional care, supporting the integration of evidence-based nutritional interventions into the comprehensive management of schizophrenia to improve metabolic and inflammatory outcomes.