Oncology nutrition research highlights the importance of medical nutrition therapy (MNT). While prevention is emphasized, nutrition’s role in metastatic cancer remains crucial. We reviewed the literature to identify nutritional challenges, key nutrients, current dietary interventions, and nutrition therapy goals for metastatic cancer. Dietary interventions can address treatment side effects and lower the risk of malnutrition. Understanding the evident link between medical nutrition therapy and patients’ treatment outcomes, quality of life, and survival may reveal therapeutic opportunities for integrating nutrition in comprehensive cancer care. Healthcare professionals must prioritize proper nutrition throughout treatment and adopt a collaborative approach to manage treatment-related side effects and malnutrition. Nutrition therapy aims to prioritize quality of life throughout cancer survivorship, and early routine malnutrition screening is crucial for timely intervention. Finally, optimizing nutrition is vital for a holistic supportive care framework and overall well-being in metastatic cancer patients.