Over the past twenty years data on the dietary fiber intake of U.S. children have been obtained from several population-based surveys. Fiber intake tends to be adequate in early childhood but drops significantly in adolescence. Adequate fiber and water intake is essential for the passage of soft stools on a regular basis. Although both types of fiber contribute to optimal gastrointestinal function, insoluble fiber plays a more significant role. The presence of insoluble fiber in the small bowel reduces transit time, and increases stool weight and frequency.
Soluble fiber absorbs water in the small intestine, increasing stool size.
It also provides fermentable substrate to colonic bacteria. Fermentation of soluble fiber by these bacteria results in the production of short chain fatty acids, which are utilized as a fuel source by the colonocytes. This is also a source of flatulence. The effects of either type of fiber are influenced by the dietary source of fiber as well as other factors that may be present in the luminal environment. A number of studies in adults also suggest a potential role for dietary fiber in preventing cancer of the colon, breast, ovaries and prostate.