The production of urinary phenols by gut bacteria and their possible role in the causation of large bowel cancer.

Epidemiological evidence is presented to relate the amount of dietary meat to the risk of large bowel cancer; it has been suggested that this may be due to the production of cocarcinogenic volatile phenols by intestinal bacteria from tyrosine. This paper describes preliminary experiments to test this suggestion. In vitro, aerobic bacteria tended to produce phenol from tyrosine while anaerobic bacteria produced p-cresol. Urine from 10 normal healthy persons contained a mean of 9.8 mg phenol/day and 51.8 mg p-cresol/day. Results from studies on patients with ileostomy, colostomy, and diverticular disease indicated that p-cresol is largely produced by the anaerobic flora of the left colon while phenol was produced in the ileum (when colonized) and cecum. In patients with familial polyposis the activity of the aerobic flora was apparently normal but there was greatly reduced amounts of p-cresol produced. The amounts of urinary volatile phenols in six patients with newly diagnosed large bowel cancer were not different from the normal values, indicating that cocarcinogenic phenols were unlikely to be a major cause of the disease.