Short-chain fatty acids dietary fiber fermentation

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. 

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. 

Highly-fermentable fiber residues, like resistant starch, oat bran, and pectin are transformed by colonic bacteria into short-chain fatty acids including butyrate. One study found that resistant starch consistently produces more butyrate than other types of dietary fiber. 

Increased fiber intake and the consumption of fruits and vegetables are well-known chemopreventive dietary strategies against colon carcinogenesis. It is reported that fiber intake reduces colonic transit time and increases the production of short chain fatty acids such as butyric acid. The latter is produced in the mammalian colon in mM concentrations as a by-product of anaerobic bacterial fermentation of dietary fiber. Butyric acid has been recognized as one candidates chemopreventive active against colon carcinogenesis because it induces apoptosis and differentiation in colon cancer cell lines. 

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