What happens to fiber in the digestive tract?
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Contrary to starch, fiber is not broken down well by our digestive enzymes. This is partly explained by the manner in which the monosaccharides are linked together. Whereas digestive enzymes (amylases) produced by people are very efficient in breaking the links between monosaccharides in starch, these enzymes are generally ineffective at breaking the links between monosaccharides in fiber. Plants build these bonds in a special way. In the stomach soluble fibers attract and bind to water and in turn form a gel-like material. This gel entraps food components such as sugars, cholesterol and fats and slowly carries them through the remaining digestive tract. Insoluble fibers, on the other hand, tend not to contribute to the formation of gels. Because soluble fibers dissolve in water, psyllium husk, inulin, FOS and others are used in supplemental fiber drinks. |
As fiber reaches the colon bacteria begin to breakdown (ferment) some of the fibers for energy and in the process produce gases such as carbon dioxide (CO2), methane gas (CH4), and hydrogen gas (H2). These gases often lead to uncomfortable bloating and flatulence associated with higher fiber intakes. Soluble fibers are more fermentable than insoluble ones. Also, other molecules, such as short-chain fatty acids, are produced by bacteria, which can be absorbed into the body. These fatty acids yield a small amount of energy and health benefits. Therefore, foods or supplements providing psyllium, beta-glucan (oats or barley), inulin, FOS, cellulose, guar gum, xanthan gum and oligosaccharides will be fermented and you can expect gas production.
What is diverticulosis and can fiber help?
Diverticulosis is a situation in which there is an out-pouching of the inner wall of the colon. This disorder is believed to be the result of increased pressure within the colon. In turn, this increased pressure is most likely the result of the highly refined diet that people choose to eat in the United States. A refined diet results in less fiber or “roughage” and thus less digestive leftovers or “residue” making its way into the colon. Less content in the colon results in a smaller diameter and greater pressure exerted upon its walls from within. It is a matter of physics, as there is an inverse relationship between the radius (r) of a collapsible tube and pressure (P) as follows:
P=1/r4
So you see, if the radius of the colon increases due to increased content then the internal pressure decreases, and vice versa. Researchers have clearly shown that those populations in the world that eat more fiber have a lower incidence of diverticulosis. Diverticulosis can lead to a medical concern called diverticulitis. Here the out-pouchings become impacted with bacteria and debris, leading to irritation, inflammation, pain, and sometimes bleeding.
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Insoluble fibers like cellulose and hemicellulose apppear to have a beneficial effect upon the formation of feces and their evacuation. Bran is an excellent source of these insoluble fibers and explains the popularity of bran breakfast cereals, muffins, and other products among individuals experiencing constipation and diverticulosis. Soluble fibers can contribute to mass and moistness of feces but not to the same extent as insoluble fiber. However, it is important to recognize that both types of fibers are beneficial and should be sought out for general digestive health. |
Can fiber promote general gut health?
Beyond diverticulosis, fiber supports general gut health. Certain fibers, particularly soluble fibers, are probiotic. Probiotic nutrients support the health of beneficial bacteria in the digestive tract. These bacteria include bifidobacterium and lactobacillus, which are major types of bacteria found in the digestive tract. There bacteria are linked to improves the health of the digestive tract and can decreases the likelihood of gut related issues such as irritable bowel disorders and certain tumors.
Are certain types of fiber good for lowering blood cholesterol levels?
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Soluble fibers include beta-glucans, mucilages, pectins, gums,and some hemi-celluloses and are purported to reduce blood cholesterol. Soluble fibers may bind to cholesterol in the digestive tract rendering them unavailable for absorption. Psyllium, oat and barley fiber are among the most advantageous providers of soluble fiber and the Food and Drug Administration (FDA) allows claims on food packages linking the consumption of these fibers to a reduction in cholesterol. Look for the following health claim on a soluble fiber containing food: |
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“The soluble fiber from psyllium seed husk in this product, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease.” |
A product must contain at least 1.7 grams of soluble fiber from psyllium seed husk per serving in order to have the health claim on its label. Additionally, there is evidence to suggest that the short-chain fatty acids (acetic, butyric, propionic, and valeric acids) and lactate produced in the colon by bacterial breakdown of soluble dietary fibers may reduce cholesterol formation in the liver. Thus, soluble fibers can inhibit cholesterol absorption from the digestive tract as well as cholesterol production in the liver. These two factors may lead to reductions in the level of cholesterol in blood; this will be explored more thoroughly in Diease/Prevention.
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