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When the term dietary fibre was first coined, over sixty years ago, it only referred to plant cell walls in the diet. [...].

Intestinal dysbiosis is thought to be an important cause of disease progression and the gastrointestinal symptoms experienced in patients with inflammatory bowel disease (IBD). Inflammation appears to be a major contributor in perpetuating a dysregulated gut microbiota. Although current drug therapies can significantly induce and maintain disease remission, there is no cure for these diseases. Nevertheless, ongoing human studies investigating dietary fibre interventions may potentially prove to exert beneficial outcomes for IBD. Postulated mechanisms include direct interactions with the gut mucosa through immunomodulation, or indirectly through the microbiome. Component species of the microbiome may degrade dietary-fibre polysaccharides and ferment the products to form short-chain fatty acids such as butyrate. Prebiotic dietary fibres may also act more directly by altering the composition of the microbiome. Longer term benefits in reducing the risk of more aggressive disease or colorectal cancer may require other dietary fibre sources such as wheat bran or psyllium. By critically examining clinical trials that have used dietary fibre supplements or dietary patterns containing specific types or amounts of dietary fibres, it may be possible to assess whether varying the intake of specific dietary fibres may offer an efficient treatment for IBD patients.

Wheat bran protects against mutations and cancer, but contains different plant cell types that are likely to have different protective effects. We previously described the production and chemical characterisation of an aleurone-rich fraction (ARF) and a pericarp-rich fraction (PRF) from wheat grain. We compared these with whole bran (WB), fed to rats as 10% of a high fat AIN-76 diet. All bran-supplemented diets increased faecal bulk, in the order PRF>WB>ARF. PRF increased the activity of NAD(P)H:quinone acceptor oxidoreductase only in the forestomach, whereas ARF and WB enhanced levels of glutathione S-transferase in the duodenum. ARF but not PRF was digested and fermented, and also encouraged bacterial growth. Rats were gavaged with the radioactive mutagen (14)C-labelled IQ (2-amino-3-methylimidazo[4,5-f]quinoline), and effects of the brans on plasma radioactivity measured. Compared with the control diet, all bran-supplemented diets reduced the concentration of radioactivity in plasma, in the order ARF>PRF>WB. All brans increased faecal elimination of radioactivity, but only ARF and PRF enhanced urinary radioactivity. These data suggest that wheat bran may reduce mutation and cancers through direct adsorption and enhanced elimination of a dietary mutagen and/or its metabolites, and that wheat bran enriched in pericarp or aleurone cell walls may exert protective effects through different mechanisms., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Wheat bran is a good source of dietary fibre in the form of cell walls, but contains a number of different cell types. We describe a large-scale procedure for the production of an aleurone-rich and a pericarp-rich fraction from hard, Australian wheat. The fractions were characterised by field-emission scanning electron microscopy, by using a range of bright-field stains, colour reagents, and fluorochromes, and by chemical analysis of the walls. The aleurone fraction included the seed coat with its cuticle. Only the pericarp walls showed a histochemical reaction for lignin. The concentrations of ester-linked ferulic acid and (1-->3),(1-->4)-beta-glucans were greater in the aleurone-rich fraction than in the pericarp-rich fraction. The results are consistent with the arabinoxylans in the walls of the pericarp-rich fraction being more highly substituted with arabinose than those in the walls of the aleurone-rich fraction. When the fractions were fed as a dietary supplement to rats and walls were isolated from the faeces, it was found that the pericarp walls were not degraded, but the aleurone walls were partially degraded.

Intestinal dysbiosis is thought to be an important cause of disease progression and the gastrointestinal symptoms experienced in patients with inflammatory bowel disease (IBD). Inflammation appears to be a major contributor in perpetuating a dysregulated gut microbiota. Although current drug therapies can significantly induce and maintain disease remission, there is no cure for these diseases. Nevertheless, ongoing human studies investigating dietary fibre interventions may potentially prove to exert beneficial outcomes for IBD. Postulated mechanisms include direct interactions with the gut mucosa through immunomodulation, or indirectly through the microbiome. Component species of the microbiome may degrade dietary-fibre polysaccharides and ferment the products to form short-chain fatty acids such as butyrate. Prebiotic dietary fibres may also act more directly by altering the composition of the microbiome. Longer term benefits in reducing the risk of more aggressive disease or colorectal cancer may require other dietary fibre sources such as wheat bran or psyllium. By critically examining clinical trials that have used dietary fibre supplements or dietary patterns containing specific types or amounts of dietary fibres, it may be possible to assess whether varying the intake of specific dietary fibres may offer an efficient treatment for IBD patients. [ABSTRACT FROM AUTHOR]

We describe preparations of plant cell walls and polysaccharides obtained from plant cell walls that are added to food products for two purposes: as modifiers of food texture and/or as dietary fibres with potential health benefits. Although a number of different types of plant cell walls occur, only some are presently exploited. Commercial ‘fibre preparations’ range from those containing mostly primary walls to those containing mostly lignified secondary walls from which much of the lignin and non-cellulosic polysaccharides have been removed. Preparations of cell-wall polysaccharides are obtained from the following sources: cellulose mostly from secondary walls of cotton and wood, pectin from primary walls of dicotyledons, and (1→3),(1→4)- β-glucans and arabinoxylans from primary walls of cereal grains. Preparations of galactomannans, xyloglucans and the pectic polysaccharide rhamnogalacturonan I are obtained from non-lignified secondary walls of certain leguminous seeds. The compositions, functionalities, uses and possible health benefits of these different preparations are discussed. [ABSTRACT FROM AUTHOR]

The dietary fiber (DF) hypothesis suggested that DF, as plant cell walls, protected against colorectal cancer. The implicit assumption in much historic literature was that the readily analyzed and quantified nonstarch polysaccharide (NSP) component was critical in cancer protection. However, the presence of polymeric phenolic components such as lignin or suberin has profound effects on the physicochemical properties of the cell walls and largely determines their physiological properties in humans. In certain groups of food plants, degradation of cell walls that contain neither lignin nor suberin releases ferulic acid and other hydroxycinnamic acids. These acids have antioxidant, antimutagenic, and other anticancer effects, including modulation of gene expression and immune response. Reexamination of literature on cancer protection suggests that plant cell walls containing significant amounts of phenolic components may be the most likely to protect against cancer. In the last 30 years, the definition of DF has been incrementally expanded to incorporate NSP extracted from plant cell walls and from sources other than plant cell walls, then resistant starch, and most recently nondigestible oligosaccharides. On the early definitions, increased consumption of DF could only be achieved by increasing the intake of whole grains, brans, or other food plant material that would increase the intake of plant cell walls containing significant amounts of phenolic components. However, the new definitions make it possible to increase "dietary fiber" without consuming any such materials. We suggest that this could have negative connotations for cancer risk in human populations. [ABSTRACT FROM AUTHOR]

Examines the role of dietary fiber (DF) in the prevention of cancer. Protective effects of cereals and DF against cancer; Determination of potential anticancer compounds in whole grain cereals; Composition of wheat bran dietary fiber.

The term 'dietary fiber' comprises a heterogeneous range of materials and both epidemiology and animal studies indicate that some dietaryfibers protect against colorectal cancer, whereas others probably donot. Recently, it has also been suggested that the different types of starches that are resistant to digestion in the small intestine ('resistant starches' or RS) protect against colorectal cancer. If true,it will be desirable to increase the amounts of resistant starches in the diet; this can be achieved more easily than comparable increases in the amounts of dietary fiber. One way that resistant starches may protect is by being degraded and fermented in the colon to yield short chain fatty acids, including butyric acid which in vitro slows the proliferation and stimulates the differentiation of colon cancer cells. Support for this hypothesis comes from in vitro studies using human fecal inocula that showed that starch was fermented to give high yields of butyrate. However, two recently published sets of animal experiments found that resistant starches did not protect against coloncancer induced by the carcinogen, dimethylhydrazine. We suggest thatfurther research is needed on the possible protective effects of resistant starches. In the meantime, we believe that a cautious approachshould be taken in the introduction onto the market place of foods that contain increased amounts of resistant starches. [ABSTRACT FROM AUTHOR]