Dietary Fiber, Bowel Health, and Cancer

Also see:
Fermentable Carbohydrates, Anxiety, Aggression
Bowel Toxins Accelerate Aging
Protective Bamboo Shoots
Endotoxin-lipoprotein Hypothesis
Endotoxin: Poisoning from the Inside Out
Protection from Endotoxin
The effect of raw carrot on serum lipids and colon function
Protective Cascara Sagrada and Emodin

“One of the factors promoting excess cortisol production is intestinal irritation, causing absorption of endotoxin and serotonin. Fermentable fibers (including pectins and fructooligosaccharides) support the formation of bacterial toxins, and can cause animals to become anxious and aggressive. Fed to horses, some types of fiber increase the amount of serotonin circulating in the blood. Grains, beans, and other seeds contain fermentable fibers that can promote intestinal irritation.” -Ray Peat, PhD

“Many doctors advise constipated patients to drink more water and exercise. While there is some physiological basis for recommending exercise, the advice to drink more water is simply unphysiological. A study in Latin America found no evidence of benefit from either of those recommendations, and recommended the use of fiber in the diet. The right kind of fiber can benefit a variety of bowel problems. However, some types of fiber can exacerbate the problem, and some types (such as oat bran) have been found to increase bowel cancer in animal studies.” -Ray Peat, PhD

Nutrition and cancer. 1998. v. 31 (1)
Dietary lignin, an insoluble fiber, enhanced uterine cancer but did not influence mammary cancer induced by N-methyl-N-nitrosourea in rats.
Previous investigations suggested potential breast cancer-preventive properties of dietary fiber from cabbage. The purpose of the present investigation was to determine whether lignin, a component of cabbage fiber, would protect against mammary carcinogenesis by N-methyl-N-nitroso-urea (MNU) in Sprague-Dawley rats. A six-week study was conducted using diets containing 0.5-5% dietary wood lignin (a readily available, purified source). These diets were well tolerated by the rats, and a carcinogenesis study using 5 mg MNU/100 g body wt iv at 50 days of age was conducted, with the 2.5% lignin diet fed from 6 through 8 weeks of age followed by 5% lignin diet until 20 weeks after MNU. Dietary lignin and MNU treatment increased food consumption (p < 0.05), and body weight was slightly reduced at 10 and 20 weeks after MNU in the MNU-5% lignin diet group (p < 0.05). Serum estradiol was not altered by dietary lignin or MNU treatment, but uterine weights were highest in the MNU-control diet group 4 and 12 weeks after MNU. Expression of creatine kinase B, an estrogen-responsive gene, was lower in the uteri of the MNU-lignin diet group than in other groups at 20 weeks. Mammary carcinogenesis was not altered by dietary lignin. However, uterine endometrial adenocarcinoma was observed only in the MNU-lignin diet group (4 carcinomas/40 effective rats) (p < 0.05).

Nutr Cancer. 1984;6(2):77-85.
Enhancement of 1,2-dimethylhydrazine-induced large bowel tumorigenesis in Balb/c mice by corn, soybean, and wheat brans.
Clapp NK, Henke MA, London JF, Shock TL.
This study was designed to determine the effects of four well-characterized dietary brans on large bowel tumorigenesis induced in mice with 1,2-dimethylhydrazine (DMH). Eight-week-old barrier-derived male Balb/c mice were fed a semisynthetic diet with 20% bran added (either corn, soybean, soft winter wheat, or hard spring wheat) or a no-fiber-added control diet. Half of each group was given DMH (20 mg/kg body weight/week, subcutaneously for 10 weeks) beginning at 11 weeks of age. Surviving mice were killed 40 weeks after the first DMH injection. Tumors were not found in mice not subjected to DMH. In DMH-treated mice, tumors were found almost exclusively in the distal colon. Tumor incidences were as follows: controls, 11%; soybean group, 44%; soft winter wheat group, 48%; hard spring wheat group, 58%; and corn group, 72%. Tumors per tumor-bearing mouse ranged from 1.4 to 1.6, except in the corn group, which had 2.1. A positive correlation was found between percentage of neutral detergent fiber in the brans and tumor incidences but not between the individual components of cellulose, hemicellulose, or lignin. The enhancement of DMH-induced large bowel tumorigenesis by all four bran types may reflect a species and/or mouse strain effect that is bran-source related. These data emphasize the importance of using well-defined bran in all “fiber” studies.

Cancer Res. 1983 Sep;43(9):4057-61.
Enhancement of rat colon carcinogenesis by wheat bran consumption during the stage of 1,2-dimethylhydrazine administration.
Jacobs LR.
These results demonstrate that dietary wheat bran, a fiber which produces a hyperproliferative response in the colon, significantly increases colon carcinogenesis when fed to rats during the stage of carcinogen administration. This effect appears to be further enhanced when the wheat bran is totally removed from the diet following the stage of carcinogen administration. These data indicate that the hyperproliferative effects of wheat bran appear to outweigh any preventive actions that bran may have on colon carcinogenesis by altering the bulk of intestinal contents and their transit time through the bowel.

Proc Soc Exp Biol Med. 1986 Dec;183(3):299-310.
Relationship between dietary fiber and cancer: metabolic, physiologic, and cellular mechanisms.
Jacobs LR.
The relationships between fiber consumption and human cancer rates have been examined, together with an analysis of the effects of individual dietary fibers on the experimental induction of large bowel cancer. The human epidemiology indicates an inverse correlation between high fiber consumption and lower colon cancer rates. Cereal fiber sources show the most consistent negative correlation. However, human case-control studies in general fail to confirm any protective effect due to dietary fiber. Case-control studies indicate that if any source of dietary fiber is possibly antineoplastic then it is probably vegetables. These results may mean that purified fibers alone do not inhibit tumor development, whereas it is likely that some other factors present in vegetables are antineoplastic. Experiments in laboratory animals, using chemical induction of large bowel cancer, have in general shown a protective effect with supplements of poorly fermentable fibers such as wheat bran or cellulose. In contrast, a number of fermentable fiber supplements including pectin, corn bran, oat bran, undegraded carageenan, agar, psyllium, guar gum, and alfalfa have been shown to enhance tumor development. Possible mechanisms by which fibers may inhibit colon tumorigenesis include dilution and adsorption of any carcinogens and/or promoters contained within the intestinal lumen, the modulation of colonic microbial metabolic activity, and biological modification of intestinal epithelial cells. Dietary fibers not only bind carcinogens, bile acids, and other potential toxins but also essential nutrients, such as minerals, which can inhibit the carcinogenic process. Fermentation of fibers within the large bowel results in the production of short chain fatty acids, which in vivo stimulate cell proliferation, while butyrate appears to be antineoplastic in vitro. Evidence suggests that if dietary fibers stimulate cell proliferation during the stage of initiation, then this may lead to tumor enhancement. Fermentation also lowers luminal pH, which in turn modifies colonic microbial metabolic acidity, and is associated with increased epithelial cell proliferation and colon carcinogenesis. Because dietary fibers differ in their physiochemical properties it has been difficult to identify a single mechanism by which fibers modify colon carcinogenesis. Clearly, more metabolic and physiological studies are needed to fully define the mechanisms by which certain fibers inhibit while others enhance experimental colon carcinogenesis.

Prev Med. 1987 Jul;16(4):540-4.
Fiber, stool bulk, and bile acid output: implications for colon cancer risk.
McPherson-Kay R.
Dietary fiber has direct effects on stool bulk and bile acid output that may be of relevance in the etiology of colon cancer. Most types of fiber increase the total volume of stool and reduce the concentration of specific substances, including bile acids, that are in contact with the bowel wall. However, fibers differ in their effect on stool bulk, with wheat fiber being a more effective stool bulking agent than fruit and vegetable fibers. In addition, the extent to which a specific fiber reduces bile acid concentration will be modified by its concomitant effects on total fecal sterol excretion. Whereas wheat bran reduces fecal bile acid concentration, pectin, lignin, and oat bran do not. These three fibers significantly increase total bile acid output. Bile acids act as promoters of colonic tumors in mutagenesis assay systems and in various animal models. Human epidemiological studies show a relationship between various dietary variables, including fat and fiber intake, fecal concentration of bile acids, and colon cancer risk.

Journal of Surgical Oncology Volume 52, Issue 2, pages 77–82, February 1993
The effect of the fiber components cellulose and lignin on experimental colon neoplasia
David A. Sloan MD, David M. Fleiszer MD, Geoffrey K. Richards MB, David Murray MB, Rea A. Brown MD
Sixty Sprague-Dawley rats were pair-fed one of three nutritionally identical diets. One diet contained “low-fiber” (3.8% crude fiber); the others contained “high fiber” (28.7% crude fiber) composed of either cellulose or lignin. Although both “high fiber” diets had similar stool bulking effects, only the cellulose diet was associated with a reduction in 1,2-dimethylhydrazine (DMH)-induced colon neoplasms. The cellulose diet was also associated with distinct changes in the gut bacterial profile and with a lowered serum cholesterol.

Food Chem Toxicol. 1984 Jul;22(7):573-8.
Effect of Metamucil on tumour formation by 1,2-dimethylhydrazine dihydrochloride in mice.
Toth B.
The effect of the plant cellulose metamucil on the tumorigenicity of 1,2-dimethylhydrazine dihydrochloride (1,2-DMH) was studied in random-bred Swiss mice. Three groups of mice, which were 5, 6 and 6 weeks old at the beginning of the experiment, were given the following treatments: (1) metamucil (20%, w/w) in powdered diet for their lifespan; (2) 1,2-DMH, ten weekly subcutaneous injections at 20 mg/kg body weight; (3) combination of treatments given to groups 1 and 2. The administration of metamucil enhanced the appearance of colon tumours induced by 1,2-DMH in males only. Metamucil had no statistically significant effect on the development of tumours elicited by 1,2-DMH at seven additional sites. It was expected that a high amount of dietary fibre would inhibit carcinogenesis in the large intestine. Instead, metamucil increased the incidence of colon tumours induced by 1,2-DMH, although only in males.

J Nutr. 1989 Feb;119(2):235-41.
Independent effects of fiber and protein on colonic luminal ammonia concentration.
Lupton JR, Marchant LJ.
The potential interactive effects of protein and fiber on cecal and colonic surface areas, colonic luminal ammonia concentrations, luminal pH and blood indices of nitrogen metabolism were tested using two levels of protein (8% and 24%) and two types of fiber (8% pectin or cellulose). Pectin supplementation resulted in larger cecal surface areas and longer large intestines than those of rats fed fiber-free or cellulose-supplemented diets. All high protein diets resulted in total large bowel luminal ammonia (NH3 + NH4+) concentrations that were twice as high as their low protein counterparts (P less than 0.05). The effect of fiber on ammonia concentration depended on the fiber type. In the distal colon, pectin-fed animals had three times the ammonia concentration of the fiber-free animals, and 4-5 times the ammonia concentration of the cellulose-fed animals (P less than 0.001). Blood urea nitrogen values were higher in the high protein than in the low protein groups (P less than 0.05), and highest in the high protein/pectin animals (P less than 0.01). This study clearly demonstrates that luminal ammonia concentration is dependent upon both protein level and fiber type, and that a fermentable fiber (pectin), rather than decreasing colonic ammonia concentrations, actually increases them several-fold.

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