In a very simplistic way, the human body has an extremely complex system of cell division that determines the growth of new cells and the death of senescent cells. However, the organism is not perfect and sometimes fails. In the course of the interaction between genetic and environmental factors, including nutritional factors, oncological disease can arise. Of course, no food alone has properties capable of preventing a tumor. In recent years there has been an increase in the number of new cases of cancer. Malnutrition in cancer patients is a consequence of the increase in inflammatory cytokines associated with cancer, metabolic alterations and concomitant inadequate availability of nutrients, due to anorexia caused by the disease and systemic treatments. Malnutrition, combined with loss of muscle mass, is very common in this group of patients and has a negative effect on the prognosis. What to expect from the doctor? It is one of the key questions in this theme.