Colonic cancer--hypotheses of causation, dietary prophylaxis, and future research.

Colonic cancer is rare in primitive populations. In western populations it was uncommon in the past, but now accounts for about 3% of all deaths. The cause almost certainly lies with dietary changes. Probably, alterations in bowel milieu interieur, from interaction between metabolites and microbacteria, promote carcinogenesis. Changes in intakes of protein, fat, sugar, refined cereal products, and crude fiber have been advanced as predisposing or causative factors. Evidence suggests that (i) fall in fiber intake, but (ii) rise in fat intake, in their ability to increase fecal concentrations of bile acids and sterols (possible precursors of carcinogens) are most likely to be culpable. As preventive measures, a significant rise in fiber intake is practicable only from regular bran ingestion. A major reduction in fat intake is grossly unlikely. Even were rigorous dietary changes implemented, an early fall in colonic cancer incidence is highly improbable due to the long-term character of the disease. Future research must include characterization of the diet, metabolism, and disease pattern of segments of western populations who have low colonic cancer mortality rates; also, elucidation of the bearing of various intakes of different food components on the biochemistry and microbiology of the feces.