Fiber, dietary fermentation

Various mechanisms have been proposed to explain the hypocholesterolemic effect of GA (Annison et al., 1995 Tiss et al., 2001). Some studies have suggested that the viscosity of fermentable dietary fiber contributes substantially to the reduction of lipids in animals and humans (Gallaher et al., 1993 Moundras et al., 1994). However, other studies suggested that this property is not related to plasma lipids (Evans et al., 1992). The mechanism involved is clearly linked to increased bile acid excretion and fecal neutral sterol or a modification of digestion and absorption of lipids (Moundras et al., 1994). 

The Influence of Fermentable Dietary Fiber on the Disposition and Toxicity of Xenobiotics... 

Short-chain fatty acids, especially butyrate, are a preferred source of energy for the colonic epithelium. There is evidence to suggest that butyrate enemas are effective in the treatment of ulcerative cohtis. The seeds of Plantago ovata (a source of fermentable dietary fiber) increase fecal concentrations of butyrate and acetate. In a randomized, open, parallel-group, multicenter study in 105 patients with ulcerative cohtis, P. ovata seeds 10 mg bd were as effective as mesalazine 500 mg tds in maintaining remission over 12 months (10). Adverse effects were similar in the two groups, and included constipation, flatulence, nausea, and diarrhea. 

Debethizy JD, Goldstein RS. 1985. The influence of fermentable dietary fiber on the disposition and toxicity of xenobiotics. In Finley JW, Schwass DE, eds. American Chemical Society Symposium Series 277. Xenobiotic metabolism Nutritional effects. Washington, DC American Chemical Society, 37-50. 

Fiber components are the principal energy source for colonic bacteria with a further contribution from digestive tract mucosal polysaccharides. Rate of fermentation varies with the chemical nature of the fiber components. Short-chain fatty acids generated by bacterial action are partiaUy absorbed through the colon waU and provide a supplementary energy source to the host. Therefore, dietary fiber is partiaUy caloric. The short-chain fatty acids also promote reabsorption of sodium and water from the colon and stimulate colonic blood flow and pancreatic secretions. Butyrate has added health benefits. Butyric acid is the preferred energy source for the colonocytes and has been shown to promote normal colonic epitheUal ceU differentiation. Butyric acid may inhibit colonic polyps and tumors. The relationships of intestinal microflora to health and disease have been reviewed (10). 

During the in vitro fermention the amount of macromolecular pectin was diminished continuously. On the other hand the fraction of OligoGalA was increased at first and diminished later. The content of short chain fatty acids, which are typical end products of fermentation of dietary fibers rised permanently (Figure 5). Low-esterified pectins were fermented in vitro faster by human faecal flora than the high-esterified pectins. 

C. difficile overgrowth is present in only 15-25% of cases of AAD thus, other explanations are needed to understand the pathophysiology of diarrhea. There are multiple mechanisms which can account for the diarrhea associated with antibiotics. These include altered fermentation of the flora, changes in dietary fiber and overgrowth of other potential pathogens. 

Goni I, Martin-Carron N. In vitro fermentation and hydration properties of commercial dietary fiber-rich supplements. Nutr Res 1998 18 1077-1089. 

Oufir LE, Barry JL, Flourie B, Cherbut C, Cloarec D, Bornet F, Galmiche JP. Relationships between transit time in man and in vitro fermentation of dietary fiber by fecal bacteria. Eur J Clin Nutr 2000 54 603-609. 

Hara, H., Suzuki, K., Kobayashi, S., and Kasai, T. (1996). Fermentable property of dietary fiber may not determine cecal and colonic mucosal growth in fiber-fed rats. /. Nutr. Biochem. 7, 549-554. 

Later it was observed that butyric acid is a naturally occurring dietary HD AC inhibitor. It is formed upon dietary fiber fermentation within our digestive system. Although butyrate does not normally reach high enough levels for cancer treatment, it has been proposed that daily consumption over an individual s lifetime may provide chemoprevenfive effects. ... 

Various processing techniques, other than fermentation, can be utilized to remove phytic acid and other dietary fiber materials that reduce mineral absorption (109). Processes would include differential extraction and filtration techniques such as ultrafiltration (125, 126, 127). 

Inicimn in particular, are readily converted into a nondigesltble or slowly digestible physical form ander certain food processing conditions. These resistant starches are readily fermented by colonic bacteria. Small amounts of waxes, cutin. and minerals in fruits and vegetables contribute to total dietary fiber values but may be physiologically inert. 

Dietary fiber has been suggested to play a protective role against chemically-induced toxicity (1) and against colon cancer (2). However, the mechanism(s) by which dietary fiber modulates chemical toxicity or colon cancer has not been well studied. The fiber fraction of the diet is resistant to mammalian digestive enzymes and consequently dietary fiber is not absorbed from the small intestine (3). However, certain types of dietary fiber specifically fermentable fibers, including the pectic substances and hemicelluloses, are readily digested by the intestinal microflora (4,5). Pectic... 

Animal feeds as well as human diets vary considerably in the type and quantity of dietary fiber. Wise and Gilbert (9) using modified detergent methods analyzed fourteen commercial rodent diets and found that the total dietary fiber content varied from 8.3 to 22.4%. In fact, it is not unusual for commercially available cereal-based rodent diets to contain 20% dietary fiber on a dry weight basis (10). In general, the fermentable fibers constitute more than half of the total dietary fiber the remainder composed of the fibers more resistant to fermentation, such as cellulose and lignin (9). Thus, a significant portion of rodent diets has the potential to be fermented in the intestinal tract. 

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