This article is from the Diet FAQ, by Claudia McCreary email@example.com with numerous contributions by others.
Fiber (also known as "roughage") is simply the non-digestible portion of the
foods that we eat. (There are actually several different types of fiber,
such as cellulose, hemicellulose, lignin, pectin, and guar.) Fiber is found
chiefly in non-processed foods such as whole grains, legumes (beans and
peas), fruits, and vegetables, especially in the outer layers of such foods.
Fiber may be added to processed foods in the form of bran, which is the
outer coating from a grain such as wheat or oats.
A high-fiber diet has a number of benefits:
* It speeds the elimination of fecal material from the body. This can reduce
or cure constipation and intestinal polyps, alleviate hemorrhoids which
often result from straining during bowel movements), and may greatly reduce
the risk of colon cancer. It may also prevent or alleviate
diverticulosis, a condition in which the intestinal lining develops small
pockets in which fecal material can be trapped.
* It fills out the stomach and intestinal cavity. This produces a sense of
fullness which is a real boon in weight control.
* It can alleviate conditions such as spastic colon and diarrhea because
fiber absorbs excess water and produces a bulkier stool.
*Some types of fibers, particularly those found in whole fruits and legumes,
tie up sugar molecules so that the levels of insulin normally
produced after eating are reduced, a big advantage for diabetics. (This
effect is most pronounced when fruits and legumes are eaten whole, rather
than as fruit juice or ground beans.)
The typical American diet is high in processed foods, most of which contain
little or no fiber. Most people get only around 10-12 grams of fiber per
day, but you need 25 grams or more to get the real benefits. If your current
diet is low in fiber, it's important that you increase fiber gradually over
a period of weeks or months; sudden increases can cause bloating, cramping,
and gas. Try having a small serving of a high-fiber, low-fat cereal with
your breakfast; as your system becomes used to the higher fiber levels,
start substituting whole-grain breads, cereals and pastas for the refined
(white flour, low-fiber) varieties you've been eating. Increase your
consumption of fresh fruits and vegetables, and consume edible peels and
skins (e.g., on apples and potatoes) rather than trimming them.