Dietary fiber intestinal enzymes

Metabolism of pectin. Pectin has only recently come, to be considered a part of the dietary fiber complex. Previously it was excluded because 1) it is not fibrous (except at the molecular level), 2) it escapes detection in standard fiber tests owing to its solubility, and 3) it usually does not survive intestinal passage. In a reassessment of which dietary components should be considered fiber, Trowell (49) proposed that dietary fiber include those constituents of food resistant to hydrolysis by man s alimentary enzymes. Spiller (50, 51) suggested that confusion surrounding the term "fiber" be avoided by using the term "plantix" to denote those plant materials of polymeric nature not attacked by human digestive enzymes. 

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... 

The digestibility of starch depends on source, physical condition, and food preparation. With the exception of lignin, dietary fibers may be partially or fully hydrolyzed by enzymes of the microflora present In the colon, iJome products arc absorbed into the bloodstream, but most serve as energy sources for the colono-cy tes. Specific dietary fibers can influence fecal bulk, the rate of passage of material through the intestines, and certain maladies such as constipation. 

A major complication of constipation in the elderly is fecal impaction, a potentially serious condition that can result from ignoring impulses to defecate. Impaction is the buildup of fecal mass that becomes too large to expel. Increasing dietary fiber is part of the management program for chronic constipation of the elderly. Addition of bran (6-20 g/day) increases fecal weight and increases the frequency of defecation. When wheat bran is not effective, the laxative lactulose is recommended. Lactulose is a disaccharide composed of galactose and fructose connected by a p(l 4) bond. This compound is absorbed poorly in the small intestine because of the absence of enzymes that catalyze its hydrolysis. 

Indigestible polysaccharides are part of the dietary fiber that passes through the intestine into the feces. Because enzymes produced by human cells cannot cleave the fi-1,4 bonds of cellulose, this polysaccharide is indigestible. 

Dietary fiber, composed principally of polysaccharides, cannot be digested by human enzymes in the intestinal tract. In the colon, dietary fiber and other nondi-gested carbohydrates may be converted to gases (H2, CO2, and methane) and short-chain fatty acids (principally acetic acid, propionic acid, and butyric acid) by bacteria in the colon. 

Dietary fiber is only one of several possible pharmacologically active substances found in foods, and present in high concentrations in leguminous seeds which may be responsible for the different rates of digestion and blood glucose responses of different meals. Enzyme inhibitors, lectins and saponins are other so called antinutritional factors, also associated with dietary fiber which are able to alter small intestinal function (48). The gastrointestinal tract evolved to deal with these constituents in foods so that while toxic in large amounts (as in uncooked beans) small amounts may have beneficial effects. 

P. may be degraded by several enzymes ftom higher plants as well as from microbial sources. The latter are responsible for p. degradation in the human large intestines and colon. Therefore, p. is considered to be a dietary fiber with important influence on cholesterol levels, on low-density lipoproteins and on glucose metabolism. 

Dietary fiber, a term used to name substances present in foods, are resistant to digestive enzymes of the human gastro intestinal tract (Phillips et al., 2008). The presence of fiber in food products is important as it assists the proper functioning of the digestive system and... 

---