Proceedings of a symposium
Wheat bran fiber and development of adenomatous polyps: evidence from randomized, controlled clinical trials

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Abstract

Mutations in oncogenes and tumor suppressor genes are thought to initiate and promote the pathway to colorectal cancer, leading to hyperproliferation, the development of adenomas, and progression to gross malignancy. Intervention at any of these steps can potentially prevent the development of cancer. Several randomized, controlled trials have investigated the effect of dietary interventions, including the addition of wheat bran fiber, on the development of adenomatous polyps. In a familial adenomatous polyposis trial, patients were treated with 4 g of ascorbic acid plus 400 mg of α-tocopherol per day alone or with a grain fiber supplement (22.5 g/day) over a 4-year period. On an actual-intake basis, the combined intervention inhibited the development of rectal polyps. However, the Toronto Polyp Prevention Trial found no significant differences in polyp recurrence rates between patients who were counseled to follow a low-fat, high-fiber diet and patients consuming a typical Western diet with placebo fiber. A 9-month study of patients with resected colon adenomas found that dietary wheat bran fiber significantly reduced total, primary, and secondary fecal bile acid concentrations and excretion rates. Such bile acid levels are thought to be related to the risk of developing cancer. The Australian Polyp Prevention Project reported that the combination of fat reduction and a supplement of wheat bran reduced the incidence of large colorectal adenomas. These latter results suggest that intervention with a low-fat wheat bran supplemented diet inhibits the transition from smaller to larger adenomas, which may be a critical step in determining which adenomas progress to malignancy.

Section snippets

The familial adenomatous polyposis trial

The familial adenomatous polyposis trial5 investigated the effects of dietary fiber, with or without supplements of ascorbic acid (vitamin C) plus α-tocopherol (vitamin E), on the development of rectal adenomas in patients with familial adenomatous polyposis. In such patients, rectal adenomas can easily be observed and counted. Each patient enrolled in the study had had a total colectomy and ileorectal anastomosis at least 1 year prior to the start of the trial. Patients were randomly assigned

Toronto polyp prevention trial

A trial conducted in Toronto6 examined the effect of dietary change on the occurrence of new colorectal adenomas in patients who had undergone a polypectomy for adenomatous polyps. Subjects (N = 201) were randomized to either a low-fat, high-fiber (LFHF) group or a normal-diet (ND) group. Those in the LFHF group received monthly counseling from a nutritionist to maintain a daily diet containing the lesser of 50 g of fat or 20% calories from fat and at least 50 g of dietary fiber. Subjects in

Wheat bran, calcium, and fecal bile acids

There is considerable evidence that bile acids play a role in colon carcinogenesis. This evidence includes the similarity in molecular structure between bile acids and known carcinogens, data from a variety of animal experiments, and population ecologic and some case–control studies of patients and those at risk that suggest a causal relationship between colorectal cancer and high levels of bile acids in the stool.7, 8 Diets containing large amounts of fat have been shown both to increase bile

Australian polyp prevention project

The Australian Polyp Prevention Project10 studied patients under surveillance for further neoplasia after resection of colorectal adenomas. Three interventions (fat reduction, wheat bran fiber supplementation, and beta-carotene supplementation) were evaluated in this study in a factorial design, resulting in eight treatment groups. Dietary fat was reduced to the point where no more than 30% of total energy (target 25%) was derived from fat. This reduction was effected by dietary counseling but

Discussion and conclusions

The evidence from these controlled, randomized trials, taken together with the evidence from epidemiologic and animal studies, supports the hypothesis that dietary wheat fiber has a protective effect against colorectal polyps and cancer.

The observation that a low-fat, wheat bran supplemented diet inhibits the development of larger adenomas10 is consistent with reports of suppressive effects of fiber on cell proliferation. A wheat bran supplement was reported to inhibit epithelial cell

References (17)

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