Fiber refers to indigestible
plant matter consumed with
food. Insoluble fiber is not water-soluble, and so passes through the
intestine and directly into the
stool. By increasing stool volume, it speeds the time to
defecation. This is thought to be healthy because when the stool moves through faster,
toxins and metabolic byproducts have less time to hang around and cause
colon cancer. Recent studies have brought this into question, but
the jury is still out.
One thing that isn't questioned is that by trapping water, insoluble fiber softens stool and may relieve
constipation. This is the basis for products like
Metamucil™. By adding bulk to the
gastric load, insoluble fiber also slows sugar absorption and reduces
blood sugar fluctuations.
Good sources of insoluble fiber include
wheat bran or
whole-wheat breads, and some vegetables.