Summary Introduction In patients with gastrointestinal (GI) cancer, severe malnutrition is associated with increased morbidity and mortality, reduction of treatment efficacy, and increased length of hospital stay. Therefore, systematic screening and care of malnutrition is mandatory. Materials and methods Data for this review were identified by searches of Medline with and without MeSH database and Cancerlit. Studies were selected only if they were randomised clinical trials or historical reports. References were also identified from reference lists in relevant preciously published articles. Recent guidelines and meta-analyses were included. Only articles published in English were taken into consideration. Results For surgical patients, practical information such as weight loss or subjective global assessment would provide a better basis for deciding whether or not to delay surgery. At least 10 days of nutritional support is recommended in severely malnourished patients before major digestive surgery. In non-severely malnourished patients, preoperative oral immunonutrition is associated with a 50% decrease in postoperative complications. The benefit of immune-enhancing diets in severely malnourished patients remains to be proven. For patients undergoing radiochemotherapy, dietary counselling should be proposed to all patients. In cases of severely malnourished patients or if dietary counselling suffers a setback, enteral nutrition should be recommended. Parenteral nutrition should be reserved for patients with severe digestive intolerance when enteral nutrition is not possible. Conclusion Propose an adaptive nutritional support at each step of a multimodal GI oncological treatment is essential. These recommendations should be used in daily practice but should also be included in all clinical research protocols.