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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
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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
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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.