Proteins and amino acids: effects of deficiencies and specific amino acids

Information about effects of protein and amino acid intake on carcinogenesis comes mainly from experiments on laboratory animals. In general, tumor formation and tumor growth are retarded in animals consuming protein- or amino acid-deficient diets, but the effects have been attributed mainly to reduced caloric intake or body weight. Nonetheless, some tumors grow well in animals consuming diets that contain levels of protein that are insufficient to meet their nutritional needs. Induction of tumors by chemical carcinogens or procarcinogens may be enhanced or inhibited in animals consuming a diet containing a particular level of protein, depending upon the responses of enzymes that activate or inactivate the specific compound being tested. The feeding of amino acid-deficient diets or amino acid antagonists has been proposed as an adjunct to chemotherapy. Undoubtedly, tumor development and growth can be influenced by the quantity of protein consumed by an animal, but the responses observed with specific tumors and carcinogens may differ. Therefore, it is not possible to draw general conclusions about effects of protein intake on the incidence of cancer or on the process of carcinogenesis.