Nutritional therapy helps patients with cancer to maintain their weight within normal limits, maintain tissue integrity and reduce the side effects of cancer therapies. Nutritional oncology deals with both prevention and patient support during treatment, in convalescence and in palliative situations. Cancer patients need full support from the team of health professionals (oncologists, nurses and dietitians). The following basic elements should not be missing from the cancer patient's diet: water, protein intake, animal and vegetable fats, as well as vitamins and minerals. The diet of cancer patients should be closely monitored, as body weight should be kept within normal limits, ie a body mass index (BMI) between 19 and 24 (the calculation is made by dividing the weight by the square of the height). The oncologist should therefore be aware of the adverse effects of malnutrition on patient outcomes and view nutritional support as an essential component of the clinical management, chemotherapy, radiation therapy, antiemetic treatment, and treatment for pain.