Slowly fermentable dietary fibers for colonic health

Dietary fiber refers to a broad class of nutrients that have differing physiological effects; the ideal dietary fiber is likely to: (1) have a low, steady rate of gas production to minimize bloating; (2) produce high levels of short chain fatty acids to prevent the growth of pathogenic bacteria and reduce inflammation; (3) ferment slowly to deliver beneficial fermentation products to all regions of the colon and prevent the production of putrefactive metabolites (e.g., ammonia, phenol); and (4) promote the maintenance of a healthy colonic microbiota by selectively stimulating the growth of beneficial bacteria or preventing the growth of undesirable bacteria. We have undertaken 3 research projects to identify such dietary fibers. First, the fermentation profiles of various dietary fiber fractions from corn, rice, and wheat bran were determined using an in vitro method. An alkali-soluble fraction from corn bran, consisting mainly of arabinoxylans, fermented slowly and produced the highest level of short chain fatty acids. Monosaccharide disappearance data suggested that corn and rice bran arabinoxylans ferment by a debranching mechanism, while wheat bran arabinoxylans contain large unsubstituted xylose regions that are utilized by bacteria first, before fermenting the more difficult to digest highly branched regions. In the second study, starch-entrapped microspheres, composites of starch and alginate, showed potential as a novel source of dietary fiber with slow fermentation characteristics, high butyrate production, and the ability to change the microbiota pattern during in vitro fermentation. The final study compared the fermentation profiles of fecal microbiota obtained from people with inflammatory bowel disease to that of healthy individuals after exposure to starch-entrapped microspheres, waxy corn starch, or fructooligosaccharides. Starch-entrapped microspheres produced more total short chain fatty acids and were more butyrogenic than fructooligosaccharides. Starch-entrapped microspheres were also superior to fructooligosaccharides with respect to preventing the growth of putative undesirable bacteria in inflammatory bowel disease