<p>Medical nutrition therapy (MNT) is a&#xa0;central component of multimodal prehabilitation. This review presents a&#xa0;selective literature review on nutrition therapy and prehabilitation in oncological gastrointestinal surgery, incorporating current guideline recommendations. Malnutrition affects up to 80% of patients with gastrointestinal cancer and is associated with increased morbidity, treatment-related toxicity, and reduced quality of life. In addition to tumor- and treatment-related factors such as dysphagia, mucositis, gastrointestinal side effects, and psychological distress, tumor-induced cachexia plays a&#xa0;pivotal role. Preoperative MNT can reduce postoperative complications and treatment discontinuations, with the greatest benefit observed in high-risk patients with manifest malnutrition. Multimodal concepts that combine MNT with physical exercise and psychosocial support show the most consistent improvements in functional capacity, postoperative outcomes, and treatment adherence. International guidelines therefore recommend multimodal strategies. Evidence-based screening and regular assessments are essential for individualized treatment planning. However, challenges remain due to limited care structures, lack of reimbursement, and unclear responsibilities within interdisciplinary management. Looking forward, standardized protocols, harmonized study designs, and integration of MNT as a&#xa0;quality criterion in cancer centers are required. Digital applications may further support adherence and standardized monitoring. Systematic implementation of MNT in oncological surgery has the potential to improve postoperative recovery, reduce treatment toxicity, and enhance patient quality of life.</p>