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Chapter 4 - Fiber Objectives • Learn the differences between dietary fiber and functional fiber and be able to give an example of each • Understand how fiber in our diet is obtained, where it is located in plants, and why it is beneficial to our health • Learn how the chemical structure of fibers influences their function in nutrition • Understand the metabolic and physiologic effects of fiber •Solubility •Water holding capacity •Adsorption • Appreciate how fiber can be used in the management and prevention of disease •Diabetes •Heart disease •GI disorders •Cancers Dietary Fiber Functional Fiber Soluble Fiber Insoluble fiber 05CO, p. 108 Table 5-1, p. 109 Fig. 5-1a, p. 110 Fig. 5-1b, p. 110 Fig. 5-1c, p. 110 Fig. 5-1d, p. 110 Fig. 5-1e, p. 110 Fig. 5-1f, p. 110 Fig. 5-2, p. 113 Fig. 5-3, p. 114 • • • High fiber: 5 g or more per serving Good source of fiber: 2.5 g to 4.9 g per serving More or added fiber: At least 2.5 g more per serving than the reference food • • • • • • • • High bile acid concentrations are associated with a high risk of colon cancer. Thus, fibers that adsorb bile acids to promote fecal excretion serve a protective effect Fibers that increase fecal bulk decrease the intraluminal concentrations of carcinogens and thereby reduce the likelihood of interactions with colonic mucosal cells. Allowance of a fermentable substrate to colonic bacteria alters kinds and numbers of bacteria and/or their metabolism, which may inhibit proliferation or development of tumor cells or conversion of procarinogens to carcinogens. A shortened fecal transit time decreases the time during which toxins can be synthesized and in which they are in contact with the colon. Fiber fermentation to short-chain fatty acids decreases the interluminal pH, thereby decreasing synthesis of secondary bile acids, which have been shown to promote the generation of tumors. Degradation of fiber by fermentation may release fiber-bound calcium. The increased calcium in the colon may help eliminate the mitogenic advantage that cancer cells have over normal cells in a low-calcium environment. Butyric acid appears to slow the proliferation and differentiation of colon cancer cells. Insoluble fibers such as lignin that resist degradation bind carcinogens, thereby minimizing the chances of interactions with colonic mucosal cells.