Correspondence The Editorial Board will be pleased to receive and consider for publication correspondence containing information of interest to physicians or commenting on.issues of the day. Letters ordinarily should not exceed 600 words, ana must be typewritten, double-spaced and submitted in duplicate (the original typescript and one copy). Authors will be given an opportunity to review any substantial editing or abridgment before publication.
Dietary Fiber TO THE EDITOR: Dr. David Kritchevsky cites in his article "Metabolic Effects of Dietary Fiber" in the February issue (West J Med 130:123-127, Feb 1979) the work of Watanabe and co-workers' who tested several dietary fibers for their effect on the appearance of chemically induced colon tumors in rats. Similarly, Cruse and associates,2 using injection of dimethylhydrazine (DMH) to induce colon cancer, recently failed to demonstrate a protective effect of dietary fiber (bran). The problem is that this kind of experimental approach is unsuitable to test the fiber/bran hypothesis. It has not been shown that parenteral DMH or one of its metabolic products (given they are carcinogenic) causes neoplastic changes from the luminal side of the colonic mucosa. According to Burkitt3 and others the addition of fiber to the diet (for example, in the form of bran) * decreases the intestinal transit-time of the feces (the reproducibility and importance of this finding is still debated), * increases persistalsis and fecal bulk, thus diluting potential carcinogens and decreasing their contact time with the bowel mucosa, * possibly affects the composition of the intestinal flora * and inhibits the bacterial degradation of bile acids and possibly other, potentially carcinogenic, fecal constituents. Hence, on the basis of these suggested mechanisms one cannot expect that fiber exhibits any protection against colonic tumors that are induced by injection rather than ingestion of carcinogens such as DMH. Even if such an approach yields a protective effect4 it must be regarded as irrelevant. The same arguments apply to the, similarly unphysiologic, intrarectal instillation of azoxymethane. Kritchevsky's suggestion that the effect of fiber in experimental colon carcinogenesis depends on
the type of fiber and the mode of administration of the carcinogen is supported by studies that use a physiologic approach to simulate the probable environmental origin of human colon cancer.56 These experimental investigations suggest that fiber (bran) may in fact be protective. As of now there is no scientific proof of the prophylactic effect of bran. However, disease prevention does not necessarily require a complete understanding of the biological mechanisms involved before some action is undertaken. Since the ill effects of bran are nil (apart from some increased flatulence in the initial stages), the effect on bowel habits is beneficial. Moreover, bran is cheap; it might well be worthwhile and feasible to change our diets by daily addition of bran. Or as Burkitt has put it: "Heads I win and tails I don't lose." MOSZE KOCHEN, MD Program in Epidemiology School of Public Health University of California, Berkeley REFERENCES 1. Watanabe K, Reddy BS, Kritchevsky D: Effect of various dietary fibers and food additives on azoxymethane or methylnitrosourea-induced colon carcinogenesis in rats. Fed Proc 37:262, 1978 2. Cruse JP, Lewin MR, Clark CG: Failure of bran to protect against experimental colon cancer in rats. Lancet 2:1278-1280, 1978 3. Burkitt DP: Large-bowel cancer: An epidemiologic jigsaw puzzle. J Natl Cancer Inst 54:3-6, 1975 4. Fleiszer D, Murray D, MacFarlane J, et al: Protective effect of dietary fiber against chemically induced bowel tumours in rats. Lancet 2:552-553, 1978 5. Wilson RB, Hutcheson DP, Widemann L: Dimethylhydrazineinduced colon tumors in rats fed diets containing beef fat or corn oil with and without wheat bran. Am J Clin Nutr 30:176-181, 1977 6. Barbolt TA, Abraham R: The effect of bran on dimethylhydrazine-induced colon carcinogenesis in the rat. Proc Soc Exp Biol Med 157:656-659, 1978 *
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Dr. Kritchevsky Replies TO THE EDITOR: I am in complete agreement with Dr. Kochen's views on the experimental approach to investigations of dietary effects on colon carcinogenesis. As he notes, I suggested in my article in the February issue that data obtained from experiments in which the putative carcinogen was administered orally were the most meaningful. Fiber may have local effects on bowel mucosal THE WESTERN JOURNAL OF MEDICINE
375
Dietary Fiber TO THE EDITOR: Dr. David Kritchevsky cites in his article "Metabolic Effects of Dietary Fiber" in the February issue (West J Med 130:123-127, Feb 1979) the work of Watanabe and co-workers' who tested several dietary fibers for their effect on the appearance of chemically induced colon tumors in rats. Similarly, Cruse and associates,2 using injection of dimethylhydrazine (DMH) to induce colon cancer, recently failed to demonstrate a protective effect of dietary fiber (bran). The problem is that this kind of experimental approach is unsuitable to test the fiber/bran hypothesis. It has not been shown that parenteral DMH or one of its metabolic products (given they are carcinogenic) causes neoplastic changes from the luminal side of the colonic mucosa. According to Burkitt3 and others the addition of fiber to the diet (for example, in the form of bran) * decreases the intestinal transit-time of the feces (the reproducibility and importance of this finding is still debated), * increases persistalsis and fecal bulk, thus diluting potential carcinogens and decreasing their contact time with the bowel mucosa, * possibly affects the composition of the intestinal flora * and inhibits the bacterial degradation of bile acids and possibly other, potentially carcinogenic, fecal constituents. Hence, on the basis of these suggested mechanisms one cannot expect that fiber exhibits any protection against colonic tumors that are induced by injection rather than ingestion of carcinogens such as DMH. Even if such an approach yields a protective effect4 it must be regarded as irrelevant. The same arguments apply to the, similarly unphysiologic, intrarectal instillation of azoxymethane. Kritchevsky's suggestion that the effect of fiber in experimental colon carcinogenesis depends on
the type of fiber and the mode of administration of the carcinogen is supported by studies that use a physiologic approach to simulate the probable environmental origin of human colon cancer.56 These experimental investigations suggest that fiber (bran) may in fact be protective. As of now there is no scientific proof of the prophylactic effect of bran. However, disease prevention does not necessarily require a complete understanding of the biological mechanisms involved before some action is undertaken. Since the ill effects of bran are nil (apart from some increased flatulence in the initial stages), the effect on bowel habits is beneficial. Moreover, bran is cheap; it might well be worthwhile and feasible to change our diets by daily addition of bran. Or as Burkitt has put it: "Heads I win and tails I don't lose." MOSZE KOCHEN, MD Program in Epidemiology School of Public Health University of California, Berkeley REFERENCES 1. Watanabe K, Reddy BS, Kritchevsky D: Effect of various dietary fibers and food additives on azoxymethane or methylnitrosourea-induced colon carcinogenesis in rats. Fed Proc 37:262, 1978 2. Cruse JP, Lewin MR, Clark CG: Failure of bran to protect against experimental colon cancer in rats. Lancet 2:1278-1280, 1978 3. Burkitt DP: Large-bowel cancer: An epidemiologic jigsaw puzzle. J Natl Cancer Inst 54:3-6, 1975 4. Fleiszer D, Murray D, MacFarlane J, et al: Protective effect of dietary fiber against chemically induced bowel tumours in rats. Lancet 2:552-553, 1978 5. Wilson RB, Hutcheson DP, Widemann L: Dimethylhydrazineinduced colon tumors in rats fed diets containing beef fat or corn oil with and without wheat bran. Am J Clin Nutr 30:176-181, 1977 6. Barbolt TA, Abraham R: The effect of bran on dimethylhydrazine-induced colon carcinogenesis in the rat. Proc Soc Exp Biol Med 157:656-659, 1978 *
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Dr. Kritchevsky Replies TO THE EDITOR: I am in complete agreement with Dr. Kochen's views on the experimental approach to investigations of dietary effects on colon carcinogenesis. As he notes, I suggested in my article in the February issue that data obtained from experiments in which the putative carcinogen was administered orally were the most meaningful. Fiber may have local effects on bowel mucosal THE WESTERN JOURNAL OF MEDICINE
375
