While there is no proof of a direct relationship between diet and cancer, evidence is accumulating to support the theory. Such evidence includes animal studies on the effects of saccharin, nitrosamines and dietary fats, tumorigenesis in energy-restricted intakes, and tumor growth in the absence of specific nutrients. Protective factors have been noted for the enzymes produced in epithelium upon ingestion of vegetables of the Brassicaceae family, and the antioxidant properties of vitamins C and E. Many surveys are contributing relevant information as to environmental and dietary factors in certain cancers, in terms of geographic variations in the incidence of colon cancer or diet variations in breast cancer, for example. Cancer and cancer treatment certainly effect nutritional status; malnutrition can be a severely disabling factor for cancer patients, due to decreased intake, malabsorption, metabolic disturbances, systemic abnormalities, or chemotherapeutic agents. Nutritional management becomes very important to maintaining quality of life, improving immunocompetence, and providing strength to undergo therapy. Many diet strategies are available, both oral and parenteral, to support nutritional intervention.