Nutritional therapy - essential in modern oncology. Malnutrition and weight loss are serious issues for many cancer patients, with severe consequences at all stages of the disease. This leads to higher therapeutic risks, increased morbidity and mortality, longer hospital stays, and a reduced quality of life for patients. Therefore, an early, individualized intervention based on current, evidence-based nutritional medical knowledge is absolutely necessary. Highlighting the connections between nutrition and cancer and translating them into practical recommendations is the significant advantage of this work. In addition to the scientific fundamentals of nutrition, methods for assessing and evaluating nutritional status, and cancer prevention through diet, the focus is on the nutritional therapy of oncology patients.