Fiber, dietary small intestine

Ebihara, K. and Schneeman, B.O. 1989. Interaction of bile acids, phospholipids, cholesterol and triglyceride with dietary fibers in the small intestine of rats. J. Nutr. 119, 1100-1106. 

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... 

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. 

After the action of salivary and pancreatic a-amylases on dietary starch and glycogen, the carbohydrate content of the small intestine consists of newly formed maltose ingested monosaccharides dietary disaccharides, such as lactose, sucrose, maltose, and trehalose oligosaccharides, such as dextrins and maltotriose and indigestible oligosaccharides and polysaccharides, such as cellulose, agar, and other oligosaccharide dietary fibers. 

Use of an intubation technique enabled Matseshe et al. (62) to show that iron introduced directly into the small intestine of human subjects in the presence of cereals was recovered less rapidly and completely than iron from ferrous sulfate or reduced iron in the presence of meat. Bran caused an 11-fold decrease in absorption of iron in the studies of McPhail et al (60). This impairment was not observed when iron was given in the form of Fe(IIl)EDTA, a response that is compatible with the ability of EDTA to release iron from its combination with dietary fiber. 

The effect of dietary wheat bran and dehydrated citrus fiber at 15% level and 5% dietary fat on intestinal carcinogenesis induced by AOM and DMAS was studied in male F344 rats (44,45). Composition of diets was adjusted so that all animals in different experimental groups consumed approximately the same amount of protein, fat, minerals and vitamins. The animals fed the wheat bran or citrus fiber and treated with AOM had a lower Incidence (number of animals with tumors) and multiplicity (number of tumors/tumor bearing rat) of colon tumors and tumors of the small Intestine than did those fed the control diet and treated with AOM (Table II 15). Although 15% purified pectin in the diet (41) inhibited the colon tumor incidence better than did 15% dehydrated citrus fiber, in this study the Inhibition of colon tumor multiplicity was more pronounced with the dehydrated citrus fiber compared with purified pectin. Because dehydrated citrus fiber contains about 20% pectin, the pectin content of this diet was considerably lower than that of the diet used in... 

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. 

Suppose you have a peanut butter and jelly sandwich for lunch. Digestion of starch from the bread begins as you chew and continues in your stomach. It is completed in the small intestine, where sugars from the jelly are also converted to monosaccharides. The indigestible carbohydrates (dietary fiber) from the bread and peanut butter pass unchanged through the small and large intestines. 

Resistant starch has also generated interest in recent times. This is starch that escapes digestion in the small intestine of healthy individuals and passes through the large intestine, where it acts like dietary fiber. Resistant starches have been classified into four main groups ... 

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