| Dietary fibers are long-chain carbohydrates (polysaccharides) that are indigestible by the human digestive tract. The value of dietary fiber is that it provides bulk to the
bolus moving through the digestive tract. There are two great advantages to this: by
bulking up the bolus, eventually the stool, it's easier for the digestive system to move
it through, and the bulkier stool also tends to retain moisture to make it easier to eliminate with less straining and
abrasion.
There are two principal types of dietary fiber: soluble and insoluble. Insoluble fiber is simply bulk that changes little as
it passes through the body. Soluble fiber, on the other hand, forms a soft gel in solution with water. Soluble fiber has been
shown to be able to reduce blood cholesterol levels and slows the absorption
of glucose from the intestine.
However, massive amounts of soluble fiber can cause diarrhea and worsen irritable bowel syndrome.
Soluble fiber is found in some fruits (particularly oranges, also apples and bananas), oats, legumes (peas, soybeans, and other
beans), other vegetables, such as broccoli and carrots, and a grain called psyllium. Legumes also typically contain
shorter-chain carbohydrates that are indigestible by the human digestive tract but which are digested by bacteria in the small
intestine, which is a cause of flatulence.
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