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.
Sources of insoluble fiber include whole wheat foods, wheat or corn bran, nuts and
seeds, vegetables such as green beans, cauliflower, and potato skins, and the skins
of fruit and root vegetables.
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