Dietary fiber and gastrointestinal disease
Koruda M.J.
Department of Surgery, University of North Carolina, Chapel Hill, NC USA
SURG. GYNECOL. OBSTET. (USA), 1993, 177/2 (209-214)
Fiber is an important physiologic component of the diet. Dietary fiber contains soluble and insoluble substrates. Soluble fiber components are fermented by colonic microflora, with the resultant production of SCFAs and gas. SCFAs are important fuels, not only for colonic mucosa, but also for the small intestine through secondary metabolism to glutamine and ketone bodies. The clinical importance of dietary fiber and its metabolic products on gastrointestinal and nongastrointestinal functions have yet to be fully realized.
Soy fiber delays disease onset and prolongs survival in experimental Clostridium difficile ileocecitis
Frankel W.L.; Choi D.M.; Zhang W.; Roth J.A.; Don S.H.; Afonso J.J.; Lee F.- H.; Klurfeld D.M.; Rombeau J.L.
Harrison Department of Surgery, University of Pennsylvania Hospital, 34th and Spruce Street, Philadelphia, PA 19104 USA
J. PARENTER. ENTER. NUTR. (USA), 1994, 18/1 (55-61)
Clostridium difficile colitis is a disabling complication in critically ill patients who commonly receive broad-spectrum antibiotics and liquid diets. To date, there is no experimental model specifically designed to investigate the effects of liquid diets on this type of colitis. The addition of fiber to liquid diets normalizes gut structure and improves absorptive function in selected conditions of intestinal dysfunction. The purposes of this study were the following: (1) to develop a reproducible model to examine the interaction of acute C difficile-induced colitis and liquid diets, (2) to determine whether the addition of soy fiber to a liquid diet improves disease, and (3) to investigate possible mechanisms of fiber-mediated disease improvement. Syrian hamsters were pair-fed with either a polymeric liquid diet or the same diet with 1.4% soy fiber for 10 days. Animals were given either clindamycin and C difficile (to produce ileocecitis), or equivalent volumes of saline. Mean survival time and systematic stool examinations for C difficile toxin positivity, liquidity, and percent water were performed to determine the effect of soy fiber on disease. Survival time was prolonged by 34% (p < .05), and C difficile toxin positivity and stool liquidity were significantly reduced (p < .05) with fiber. Additional animals were studied to determine possible mechanisms for improved survival in fiber-supplemented animals. Cecal histology, colonic water absorption, cecal microflora, and gastric to anus transit time were measured in these animals. Colonic water absorption and gastric to anus transit time were significantly increased (p < .05) and decreased (p < .05) with fiber, respectively. A hamster model of C difficile ileocecitis has been designed to investigate the effects of liquid diets. Fiber supplementation prolongs survival in this model due in part to a delay in onset of C difficile infection and improved colonic water absorption.
Intestinal immunocompetency and/or cancer control
Biotherapy (Japan), 1997, 11/4 (524-525)
The conditions and diseases that have become more prevalent are almost wholly of environmental origin. The most plausible contributory factor is diet. In diet, calorie intake has increased, total intake of protein has risen, and more animal but less vegetable protein is consumed. Dietary fiber is described as the proportion of plant foods not digested in the human small intestine. For the purpose of practical classification, dietary fiber is divided into 'water soluble' and 'water insoluble' types. The soluble fibers (pectins and gums) slow glucose absorption, and reduce serum cholesterol. Insoluble fibers (cellulose, hemicelluloses, and lignin) decrease intestinal transit time and increase fecal bulk, thus preventing colon cancer. Among the various kinds of pectin, apple pectin exerts a bacteriostatic action and therefore may change the composition of the intestinal flora. The diet supplemented with 20% apple pectin significantly decreased the number and the incidence of AOM-induced colon tumors in rats. Fecal beta-glucuronidase activity was significantly lower in the group fed pectin. The prostaglandin E2 (PGE2) level in the distal colonic mucosa and blood of portal vein was lower in rats fed 20% pectin than those fed the basal diet. The ability of apple pectin to decrease PGE2 was dose-dependent, and those results suggest an anti-inflammatory effect in the bowel. Rats fed apple pectin showed a significantly lower incidence of hepatic metastasis than those fed the basal diet. To determine whether the anti-inflammatory effect of Lactobacillus on the hepatic metastasis model was the same as apple pectin, Lactobacillus casei was selected. Metastatic nodules were significantly reduced, especially in the group receiving pretreatment. The suppression of colonic carcinogenesis in AOM induced colon tumors in rats was evident with three kinds of living bacterial mixture (S. faecalis, B. mesentericus, C. butyricum). In conclusion, apple pectin has a scavenger effect in the intestinal digestion and portal circulation system as an anti-inflammatory food. Dietary fibers like pectin, and Lactobacillus have a very important function in the intestinal tract as anti-inflammatory foods.
Endoscopic evaluation of the preventive effect of wheat bran against 1,2-dimethylhydrazine induced large bowel carcinogenesis in rats
Nutrition Research (USA), 1996, 16/9 (1521-1527)
We evaluated the preventive effects of wheat bran (40%, weight percent of diet) on the development of large bowel carcinoma induced by weekly intraperitoneal administration of 25 mg/kg (body weight) of 1,2- dimethylhydrazine over 19 weeks in the rat. Feces number and volume per pellet in wheat bran diet group were significantly greater than those in basal diet group, and the induction rates of tumor in the wheat bran diet group was found to be significantly lower than that in the basal diet group. These results suggested that wheat bran was effective in inhibiting large bowel carcino the increased fecal weight and volume from wheat bran may be involved in such an inhibitory effect.
Wheat bran and psyllium diets: Effects on N-methylnitrosourea-induced mammary tumorigenesis in F344 rats
Journal of the National Cancer Institute (USA), 1996, 88/13 (899-907)
Background: Experimental and epidemiologic evidence suggests that increased dietary fiber is associated with decreased breast cancer risk. Little is known about the role played by different types of fiber and, particularly, mixtures of soluble and insoluble fibers similar to those consumed by human populations in reducing breast cancer risk. High intake of fiber may suppress bacterial hydrolysis of biliary estrogen conjugates to free (absorbable) estrogens in the colon and thus may decrease the availability of circulating estrogens necessary for the development and growth of breast cancers. Purpose: The purpose of this study was to evaluate the effect of wheat bran (an insoluble fiber) and psyllium (a soluble fiber) alone and in combination on overall estrogen status, on fecal bacterial beta- D-glucuronidase (a key diet-responsive estrogen-deconjugating enzyme) activity, and on the induction of mammary tumors in rats treated with N- methylnitrosourea (MNU). Methods: One hundred fifty virgin female F344 rats were fed the NIH-07 diet from 28 days of age until 50 days of age; they were then given a single dose (40 mg/kg of body weight) of MNU by tail vein injection. Three days later, they were randomly assigned to one of five experimental dietary groups (30 animals per group). Soft, white wheat bran (45% dietary fiber content) and psyllium (80% dietary fiber content) were added to a modified (high-fat) American Institute of Nutrition (AIN)-76A diet at the following percents, respectively: 12% + 0% (group 1), 8% + 2% (group 2), 6% + 3% (group 3), 4% + 4% (group 4), and 0% + 6% (group 5). Blood, urine, and feces were collected and analyzed by radioimmunoassay techniques for estrogens. Cecal contents were analyzed for bacterial beta-D-glucuronidase activity. After 19 weeks on the experimental diets, the rats were killed, and mammary tumors were counted and classified by histologic type. Cumulative tumor incidence was evaluated by the Kaplan-Meier life-table method and the logrank test. Tumor number was evaluated by the chi-squared test of association, and tumor multiplicity was evaluated by the Mantel-Haenszel chi- squared test. All statistical tests were two-tailed. Results: As the level of psyllium relative to that of wheat bran increased, the total tumor number and multiplicity of mammary adenocarcinomas in rats decreased as a statistically significant linear trend across groups 1-5 (P<.05). Compared with the group given wheat bran alone, the group given the 1:1 (wheat bran:psyllium) combination had maximum protection against mammary tumorigenesis, while the groups given the 4:1 or 2:1 (wheat bran:psyllium) combination or psyllium alone bad intermediate protection. No statistically significant differences in circulating estrogens or urinary estrogen excretion patteoups. Fecal estrogen excretion, however, decreased with increasing levels of psyllium (P<.01), and cecal beta-D- glucuronidase activity exhibited a decreasing trend with respect to the increasing psyllium content of the diet across groups 1-5 (P<.01). Conclusions: The addition of a 4%:4% mixture of an insoluble (wheat bran) fiber and a soluble (psyllium) fiber to a high-fat diet provided the maximum tumor-inhibiting effects in this mammary tumor model. Although increasing levels of dietary psyllium were associated with decreased cecal bacterial beta- D-glucuronidase activity, these changes were not reflected in decreased circulating levels of tumor-promoting estrogens. Therefore, the mechanism(s) by which mixtures of soluble and insoluble dietary fibers protect against mammary tumorigenesis remains to be clarified.
Influence of dietary protein, fat, and fiber on growth, blood chemistry, and tumor incidences in Fischer 344 rats
Nutrition and Cancer (USA), 1996, 25/3 (269-279)
Composition of diets may influence growth, diseases, tumor rates, and responses to chemical treatment. For two years, Fischer 344 rats were fed the NIH-07 open-formula nonpurified diet (similar23% protein, similar5% fat, and similar3.5% fiber) and nonpurified experimental diets (NTP-90, NTP-91, and NTP-92) containing lower protein and higher fat and fiber (14.6-15.3% protein, 7.2- 8.5% fat, and 9.4-14% fiber) than the NIH-07 diet. Rats were evaluated for growth patterns, survival, hematology, serum chemistry, nephropathy, and tumor incidences. Growth patterns were similar in rats fed the experimental diets and in those fed the NIH-07 diet. However, in rats fed the experimental diets, the adult body weights were significantly (6-9%) lower and the survival at 110 weeks of age was significantly higher (15-20%) than in rats fed the NIH-07 diet. Lower protein content of experimental diets decreased the severity of nephropathy. Higher fat content of experimental diets appears to have decreased the incidence or delayed the development of leukemia and associated mortality in males. Higher fiber content of experimental diets appears to have delayed the development of mammary tumors and associated mortality in females. Higher fat and/or fiber of the experimeochromocytomas in males. The lower protein and higher fat and fiber contents of the experimental diets decreased the spontaneous tumor burden in two-year studies. These studies indicate that diets for rats in long-term studies could be modified to decrease the severity of nephropathy and to decrease/delay the development of spontaneous tumors.
The adsorption of heterocyclic aromatic amines by model dietary fibres with contrasting compositions
Chemico-Biological Interactions (Ireland), 1996, 100/1 (13-25)
It is often recommended that consumption of dietary fibre should be increased to protect against colorectal cancer. However, although more than 95% of dietary fibre is contributed by whole plant cell walls, very little experimental work has been done using whole plant cell walls. These may protect by adsorbing carcinogens, thus lowering their effective concentration in the alimentary tract, and by carrying the carcinogens out of the body in the faeces. However, plant cell walls vary widely in their composition and physical properties, and not all cell walls will necessarily have protective properties. We therefore isolated 4 plant cell-wall preparations with contrasting compositions as models of the types of cell walls that occur in the diet. We investigated the abilities of these preparations to adsorb in vitro 6 heterocyclic aromatic amines (HAAs). HAAs occur in the human diet and several are colon carcinogens, at least in rats. We found that the ability of the HAAs to adsorb to the plant cell walls increased with increasing hydrophobicity of the HAA, measured as the calculated logarithm of the partition coefficient between 1-octanol and water (C logP). A cell-wall preparation containing mainly the walls of parenchyma cells (the most common cell type in food plants) had only poor adsorptive ability. A cell-wall preparation from commercial cork had the best adsorptive ability. This preparation was the most hydrophobic of those examined because the cell walls contained the polymer, suberin, together with associated waxes. The preparation modelled suberized cell walls which occur in the diet, for example in potato skins. The other two cell-wall preparations contained another hydrophobic polymer, lignin, and had intermediate adsorptive abilities which were not significantly different from one another. These preparations modelled lignified cell walls which occur in the diet, for example in wheat bran. Our results indicate that suberized and lignified cell walls may be important in protecting against colorectal cancer.
Dietary fiber and the chemopreventive modelation of colon carcinogenesis
Mutation Research - Fundamental and Molecular Mechanisms of Mutagenesis (Netherlands), 1996, 350/1 (185-197)
Comparative international epidemiological data indicate that the difference between the highest and lowest colon cancer incidence is approximately 10-fold. This suggests that the dominant causes of colon cancer are environmental rather than genetic in origin, with the dominant environmental cause being the typical diet of Western industrialized countries. Many epidemiological and experimental studies have suggested an important role for dietary fiber in the prevention of colon data clearly demonstrate a strong protective effect of a diet that is low in fat, high in fiber and high in calcium (low-risk diet). Such a diet prevents the development of both preneoplastic aberrant crypt foci (ACF) and colon tumors. Recent experiments have also demonstrated a direct relationship between a ras point mutation in ACF at different stages of rat colon carcinogenesis, and a ras point mutation that is subsequently present in colon tumors. Using wheat bran as the model dietary fiber source, its effects were compared to the effects of psyllium, phytic acid, vitamin E, beta-carotene, folic acid, alone or in combination, for their ability to prevent colon cancer in rats on high-risk Western-style diets. Our studies clearly demonstrated the ability of wheat bran to reduce ACF and colon tumors in rats that consumed high-fat, Western-style diets. Although phytic acid, which is a constituent of wheat bran, alone demonstrated strong cancer-preventive potential, our experiments provided evidence for the cancer-preventive effect of the crude fiber fraction that is independent of the effect of phytic acid. The synergistic combination of wheat bran with the soluble fiber psyllium led to enhanced protection; while the combination of wheat bran with beta-carotene showed only an additive effect. beta-Carotene appeared to show higher protection than wheat bran at an intake level that is nutritionally relevant to humans, suggesting the possibility of using beta-carotene to enhance the effects of dietary fiber in high-risk Western populations. Using ACF as an intermediate endpoint, it was also shown that vitamin E and beta-carotene appear to inhibit progression of ACF to colon cancer, while wheat bran and folic acid appeared to have weak cancer-preventive potential at this late stage of carcinogenesis. In conclusion, wheat bran alone, or in combination with psyllium, appears to have greater potential to inhibit earlier phases of carcinogenesis, while beta-carotene and vitamin E may also inhibit later stages of carcinogenesis. Despite considerable epidemiological and experimental evidence that increasing the fiber and lowering the fat content of the Western diet could substantially reduce the risk of cancer and heart disease, the real challenge is to find effective ways to educate and motivate people to overcome their intrinsic cultural resistance to such changes in their eating habits.
Studies on the role of specific dietary fibres in protection against colorectal cancer
Mutation Research - Fundamental and Molecular Mechanisms of Mutagenesis (Netherlands), 1996, 350/1 (173-184)
Although dietary fibre is generally thought to protect against the development of colorectal cancer, some of the results of animal and epidemiological studies are equivocal. We believe that this may be because the term dietary fibre covers a range of complex materials and some may protect but others may not. Dietary fibre is mainly composed of plant cell walls which vary in composition and properties according cell type and plant species. In addition to polysaccharides, the walls of some plant cell types contain the hydrophobic polymers lignin or suberin. Two groups of mechanisms have been proposed for the way dietary fibres may protect against colorectal cancer: those in which the dietary fibre may act directly and those in which the dietary fibre may have an indirect effect as a consequence of it being degraded by colonic bacterial enzymes and the products fermented. Direct mechanisms include the adsorption of carcinogens onto undegraded dietary fibres which pass out of the intestinal tract in the faeces. We have shown that different types of plant cell walls adsorbed a range of carcinogens, including heterocyclic aromatic amines, to different extents. Cell walls that contained lignin or suberin adsorbed hydrophobic carcinogens particularly well. Furthermore, the presence of lignin, and probably suberin, in the walls makes them resistant to degradation in the colon. Wheat bran, which is a good source of dietary fibre, contains some cell types with lignified walls. We used Fischer-344 rats to test the ability of wheat bran to protect against the formation of aberrant crypts (which are considered to be precursors to colon cancer) caused by the heterocyclic aromatic amine, 2-amino-3-methylimidazo(4,5-f)qu inoline (IQ). Our results indicate that wheat bran protects and probably does so by a direct mechanism.
Benefits of dietary fiber: Myth or medicine?
Postgraduate Medicine (USA), 1996, 99/2 (153-154+156+166-168+171-175)
In recent years, many health claims have been made about dietary and supplemental fiber. However, some reports (eg, those regarding oat bran) have been controversial. A review of scientifically rigorous studies shows that fiber has some preventive or therapeutic benefits in irritable bowel syndrome, diverticulosis, colorectal cancer, diabetes, and hypercholesterolemia. However, it appears to have no direct benefit in patients with inflammatory bowel disease, gallstones, or obesity. The United States has one of the lowest per capita intakes of fiber in the world. Therefore, increasing daily fiber intake either through diet or with supplements is recommended for most Americans. Consumer interest groups should lobby for more fiber-enriched foods. The challenge for education and healthcare professionals alike is to remold the nation's interest in and understanding of dietary fiber.
