The relationship between cancer and diet is supported by epidemiological evidence suggesting that diet is a factor in the development of cancer of various organs including the esophagues, stomach, liver, and large bowel. The role of depressed immunocompetency, especially during critical periods of growth and development, is stressed as a possible important consequence of nutritional insults leading to carcinoma. Study of the relationships among nutritional factors, host-defense mechanisms, and carcinogens to carcinogenesis is significant since, theoretically, manipulation of diet could suppress or prevent chemically induced cancers. The distinction should be emphasized, however, between “nutrients,” those elements of one's intake that are essential because the body is unable to synthesize them de novo, and “diet,” which refers to everything that is ingested. It is the components of diet, chemicals in particular, that are most convincingly implicated as carcinogens, while it is doubtful that nutrient deficiencies or excesses have a direct causal relationship with the onset or development of cancer. Rather, nutrition probably exerts it carinogenic effects indirectly; nutrients possibly enhance chemical carcinogenesis multifactorially by mechanisms linked to their ability to: (a) act as carriers of carcinogens or their precursors; (b) alter intestinal flora so that carcinogenic reactions are facilitated; (c) enhance levels and reactivity of cocarcinogens; (d) influence absorptive properties or morphology of tissues so that carcinogenic activity is enhanced; and/or (e) modify host-defense mechanisms that normally protect that organism.
Presented at the Conference on Nutrition in the Causation of Cancer, May 19 to 22, 1975, Key giscayne, Fla. Supported by Grants AA0-23 from the National Institute of Alcohol Abuse and Alcoholism, CA 16750 from the National Cancer Institute, 3057-41 from the General Research Support, Boston City Hospital, 508 from the Nutrition Foundation, Inc., and Contract HSM-42-72-195 from the National Institute of Alcohol Abuse and Alcoholism.