Human and laboratory studies on the causes and prevention of gastrointestinal cancer.

Neoplasms affecting different subsections of the large bowel appear to have different risk factors. For the major type of neoplastic disease in the large bowel, that in the descending and sigmoid colon, a good association with nutrition and specific nutritional elements has been found. The risk of this type of colon cancer is proportional to the customary dietary fat intake--high in the Western World and low in the Orient. It is inversely proportional to stool bulk, which is itself modulated by cereal fibre intake. Fat and fibre, as the two major elements implicated, are sufficiently secure with regard to underlying scientific data and understanding of mechanisms, to permit utilising them to modify risk. Thus, a dietary regimen low in total fat, 20% of calories, and higher in cereal fibre, of the order of 30 grams/day, is indicated. Such a modified nutritional intake could be expected to reduce risk, not only in the general population, but most likely also in patients who have been treated successfully by conventional means. Additional evidence suggests that regular intake of yellow and green vegetables, of foods containing calcium salts, selenium and other micro-nutrients, lower the risk even more. More research is needed to provide the data necessary for deliberate intervention with these agents. Gastric cancer, on the other hand, has a distinct set of risk factors, namely, intake of pickled and salted fish or beans. Other risk factors are associated with residence in areas where the geochemical or agricultural sources of nitrate intake are not balanced by the presence of vitamin C, vitamin E, or certain phenolic antioxidants and nitrite traps such as pyrogallol, tannins, or peptides. The possible genotoxic carcinogen is not yet known, but it could be an alkyl-nitrosamide type of aryldiazonium chemical. The formation of such compounds is inhibited by vitamin C, vitamin E, and certain antioxidants. This fact can be used to decrease deliberately the risk of gastric cancer.