Possible role of nutrients in neoplasia.

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 esophagus, 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 its carcinogenic 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 the organism.