Fermentative characteristics of cereal brans and vegetable fibers
TL;DR: It is concluded that vegetable fibers may more effectively stimulate colonic fermentation than cereal brans do and suggest an attribute (i.e., fermentability) that may partially explain previously observed differences between vegetable and cereal fiber consumption patterns and colorectal carcinogenesis.
Abstract: Dietary fiber has been suggested to alter the colonic environment and protect against colorectal diseases, but several recent epidemiological studies indicate that cereal and vegetable fibers may not confer the same benefit. To address this issue, five common cereal brans (barley, corn, oat, rice, and wheat) and five vegetable fiber isolates (broccoli, cabbage, carrot, cauliflower, and lettuce) were fermented in vitro with human fecal microbiota for 4, 8, 12, and 24 hours. Short‐chain fatty acid (SCFA), hydrogen (H2), and methane (CH4) productions and neutral‐detergent fiber (NDF) digestibility differed significantly with fiber source. The vegetable fibers were significantly more fermentable than were the cereal brans, as evidenced by greater NDF digestibility and increased productions of SCFA, H2, and CH4, despite the presence of fermentable starch and protein in the latter. We concluded that vegetable fibers may more effectively stimulate colonic fermentation than cereal brans do. These finding...
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TL;DR: Resistant starch is a prebiotic, but knowledge of its other interactions with the microflora is limited and the contribution of RS to fermentation and colonic physiology seems to be greater than that of NSP.
Abstract: Resistant starch (RS) is starch and products of its small intestinal digestion that enter the large bowel. It occurs for various reasons including chemical structure, cooking of food, chemical modification, and food mastication. Human colonic bacteria ferment RS and nonstarch polysaccharides (NSP; major components of dietary fiber) to short-chain fatty acids (SCFA), mainly acetate, propionate, and butyrate. SCFA stimulate colonic blood flow and fluid and electrolyte uptake. Butyrate is a preferred substrate for colonocytes and appears to promote a normal phenotype in these cells. Fermentation of some RS types favors butyrate production. Measurement of colonic fermentation in humans is difficult, and indirect measures (e.g., fecal samples) or animal models have been used. Of the latter, rodents appear to be of limited value, and pigs or dogs are preferable. RS is less effective than NSP in stool bulking, but epidemiological data suggest that it is more protective against colorectal cancer, possibly via butyrate. RS is a prebiotic, but knowledge of its other interactions with the microflora is limited. The contribution of RS to fermentation and colonic physiology seems to be greater than that of NSP. However, the lack of a generally accepted analytical procedure that accommodates the major influences on RS means this is yet to be established.
2,702 citations
TL;DR: Efforts to increase dietary fiber in individuals consuming <25 g/day may help to decrease the currently high national prevalence of obesity.
Abstract: The influence of dietary fiber on energy regulation remains controversial. This review summarizes published studies on the effects of dietary fiber on hunger, satiety, energy intake, and body composition in healthy individuals. Under conditions of fixed energy intake, the majority of studies indicate that an increase in either soluble or insoluble fiber intake increases postmeal satiety and decreases subsequent hunger. When energy intake is ad libitum, mean values for published studies indicate that consumption of an additional 14 g/day fiber for >2 days is associated with a 10% decrease in energy intake and body weight loss of 1.9 kg over 3.8 months. Furthermore, obese individuals may exhibit a greater suppression of energy intake and body weight loss (mean energy intake in all studies was reduced to 82% by higher fiber intake in overweight/obese people versus 94% in lean people; body weight loss was 2.4 kg versus 0.8 kg). These amounts are very similar to the mean changes in energy intake and body weight changes observed when dietary fat content is lowered from 38% to 24% of energy intake in controlled studies of nonobese and obese subjects. The observed changes in energy intake and body weight occur both when the fiber is from naturally high-fiber foods and when it is from a fiber supplement. In view of the fact that mean dietary fiber intake in the United States is currently only 15 g/day (i.e., approximately half the American Heart Association recommendation of 25-30 g/day), efforts to increase dietary fiber in individuals consuming <25 g/day may help to decrease the currently high national prevalence of obesity.
1,001 citations
TL;DR: It is concluded from this review that "nondigestible fructo-oligosaccharides," even though they are not included in the carbohydrate fraction that is quantified as dietary fiber by classic analytical methods, have most of the physiological effects of a dietary fiber.
Abstract: Dietary fiber is a general term. It covers a wide variety of substances that belong to the family of carbohydrates that resist hydrolysis by human alimentary enzymes but are fermented by colonic microflora. The main physiological effects of dietary fiber are primarily on gastric emptying and small intestinal transit time, resulting in an improved glucose tolerance and a decreased digestion of starch: second, on colonic transit time and large bowel functions due to fermentation by ceco-colonic microbial flora or bulking action. The so-called soluble dietary fibers are fermented to a large extent by a wide variety of anaerobic bacteria that result in an increase in bacterial biomass, an increase in fecal mass, a change in intracolonic pH, and production of short chain fatty acids and various gases as metabolic end products. The insoluble fibers are only marginally fermented: they serve almost exclusively as bulking agents that result in shorter transit time and increased fecal mass. The short chain fatty acids resulting from the colonic fermentation of dietary fiber are largely absorbed via the portal blood and reach both the liver and the peripheral tissues. They induce changes in glucose and fat metabolism leading to post-prandial hypoglycemia and long-term hypolipidemia. Inulin and oligofructose are fructans with a degree of polymerization of 2 to 60 and 2 to 20, respectively. Due to the structural conformation of their osidic bridge (beta 2-1), they both resist the hydrolysis by human alimentary enzymes. Moreover, when reaching the colon, both inulin and oligofructose are almost quantitatively fermented almost exclusively by colonic bifidobacteria and bacteroides. Such an extensive fermentation causes an increase in fecal bacterial biomass, a decrease in ceco-colonic pH, and produces a large amount of fermentation products among which the short chain fatty acids that exert systemic effects on lipid metabolism. Thus, both inulin and oligofructose have most of the characteristics of a dietary fiber and the proposal is made to classify them as such. Moreover, they are bifidogenic factors, because, due to still unknown reasons, they are primarily fermented by bifidobacteria. It is concluded from this review that "nondigestible fructo-oligosaccharides," even though they are not included in the carbohydrate fraction that is quantified as dietary fiber by classic analytical methods, have most of the physiological effects of a dietary fiber.(ABSTRACT TRUNCATED AT 400 WORDS)
643 citations
TL;DR: Lignan production with the in vitro method related well to the urinary lignan excretion observed in rats and humans and should be useful in the estimation of lignans production from a given diet and in the formulation of high-lignan-producing diet for the purpose of reducing the cancer risk.
Abstract: Mammalian lignans such as enterolactone and enterodiol, which are produced in the colon from precursors in foods, have been suggested as playing a role in the cancer‐protective effect of vegetarian diets. Despite this, very little is known regarding the amount that is produced from different food products. Therefore, the objective of this study was to determine the production of mammalian lignans from 68 common plant foods by using the technique of in vitro fermentation with human fecal microbiota, which simulates colonic fermentation. Results showed a wide range (21–67,541 μg/100 g sample) in the amount of lignans produced. On the average as a group, the oilseeds produced the highest amounts (20,461 ± 12,685), followed by the dried seaweeds (900 ± 247), whole legumes (562 ± 211), cereal brans (486 ± 90), legume hulls (371 ± 52), whole grain cereals (359 ± 81), vegetables (144 ± 23), and fruits (84 ± 22). The vegetables produced the second highest concentration of lignans (1,546 ± 280) when the d...
624 citations
TL;DR: The studies suggest that the chemopreventive benefits of butyrate depend in part on amount, time of exposure with respect to the tumorigenic process, and the type of fat in the diet.
Abstract: All dietary fiber, by definition, escapes digestion in the small intestine and thus arrives relatively intact in the large intestine. Its fate in the large intestine depends upon the type of fiber and the colonic microflora. Highly fermentable fibers result in short chain fatty acids including butyrate, which is thought by some to be protective against colon cancer. However, not all studies support a chemopreventive effect for butyrate and the lack of agreement (particularly between in vivo and in vitro studies) on butyrate and colon cancer has been termed the "butyrate paradox." There are a number of reasons for this discrepant effect including differences between the in vitro and in vivo environments, the timing of butyrate administration, the amount of butyrate administered, the source of butyrate (usually dietary fiber) as a potential confounder, and an interaction with dietary fat. Collectively, the studies suggest that the chemopreventive benefits of butyrate depend in part on amount, time of exposure with respect to the tumorigenic process, and the type of fat in the diet.
314 citations
References
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01 Jan 1970
5,332 citations
TL;DR: It seems likely that carcinogens produced by the action of an abnormal bacterial flora when held for a prolonged period in a concentrated form in contact with the bowel mucosa may account for the high incidence of these diseases in economically developed countries.
Abstract: All experimental studies in cancer are eventually aimed at limiting or curing the disease. When relationships have been established between environmental factors and the incidence of a particular disease, whether benign or malignant, evasive action can be taken before the actual causative agents or mode of action is understood. Cholera was evaded by the avoidance of sewage-contaminated water a century before the v. cholera was identified as the cause of the disease. Lung cancer can largely be avoided by abstinence from smoking cigarettes, although the carcinogenic mechanism whereby tobacco smoke causes cancer is not yet understood. A relationship can be demonstrated between certain bowel diseases and diet, and although this has not yet been shown to be causitive in the case of cancer, the relationship between an over-refined diet and diverticular disease can now be considered established. In view of the evidence, it seems justifiable to issue a warning against the removal of so much of the unabsorbable fiber from our food, and the associated over-ingestion of refined carbohydrates.
1,219 citations
TL;DR: The hypothesis is put forward that fatty acids of anaerobic bacteria are a major source of energy for the colonic mucosa, particularly of the distal colon.
Abstract: Suspensions of isolated epithelial cells (colonocytes) from the human colon were used to assess utilisation of respiratory fuels which are normally available to the colonic mucosa in vivo. Cells were prepared from operative specimens of the ascending colon (seven) and descending colon (seven). The fuels that were used were the short chain fatty acid n-butyrate, produced only by anaerobic bacteria in the colonic lumen, together with glucose and glutamine, normally present in the circulation. The percentage oxygen consumption attributable to n-butyrate, when this was the only substrate, was 73% in the ascending colon and 75% in the descending colon. In the presence of 10 mM glucose these proportions changed to 59% and 72%. Aerobic glycolysis was observed in both the ascending and descending colon. Glucose oxidation accounted for 85% of the oxygen consumption in the ascending colon and 30% in the descending colon. In the presence of 10 mM n-butyrate these proportions decreased to 41% in the ascending colon and 16% in the descending colon. Based on the assumption that events in the isolated colonocytes reflect utilization of fuels in vivo, the hypothesis is put forward that fatty acids of anaerobic bacteria are a major source of energy for the colonic mucosa, particularly of the distal colon.
1,181 citations
TL;DR: The modification described utilizes a serum bottle closed with a butyl rubber stopper with a crimped metal seal for the growth of obligately anaerobic bacteria.
Abstract: The modification described utilizes a serum bottle closed with a butyl rubber stopper with a crimped metal seal for the growth of obligately anaerobic bacteria.
821 citations
Journal Article•
TL;DR: A comparison of dietary intake and faecal characteristics in population samples from two areas of Denmark and Finland with 4-fold variation in colon-cancer incidence suggests that the aetiology of colon cancer may be multifactorial and is not associated in a simple manner with dietary fat, neutral steroids, acid steroids, or their bacterial metabolites.
716 citations