Fiber
Although classified as a carbohydrate, fiber
supplies no vitamins, minerals or even calories. It does,
however, play important roles in the body.
Basically, there are two types of fibers: those that
dissolve in water (water-soluble or soluble fiber) and those that don't
(water-insoluble or insoluble fiber).
The water-soluble fibers — pectins, gums and
mucilages — are found mainly in citrus fruits, apples, potatoes, dried
peas and beans, oatmeal and oat bran. In the body, they bind bile
acids and as the acids are bound, cholesterol is withdrawn from the
blood and converted to bile acids to replace the deficit. The
cholesterol lowering effect may be subtle; still, it reduces the risk of
heart disease. Water-soluble fiber also lowers or at least
stabilizes blood sugar (glucose) levels. Intricately bound
to digestible carbohydrates, which the body breaks down to form glucose,
fiber slows down the digestion of carbohydrates and subsequent release
of glucose into the blood.
The two most common water-insoluble fibers, cellulose
and lignin, form the framework of plant cell walls. Neither cellulose
(found in wheat bran, whole wheat, whole-grain breakfast cereals,
broccoli and carrots) nor lignin (asparagus, wheat bran and pears) will
dissolve in water, but both have the ability to absorb it. This means
they bulk up stools and speed the passage of waste through the
intestines, functions believed to reduce the risk of colon cancer.
Many grains, brans, fruits and vegetables contain both
types of fiber. But no animal food (meat, eggs, milk, cheese, etc.)
provides any fiber whatsoever.
If you haven't been eating enough fiber, it's wise to
increase your intake slowly. Doing so all at once can cause gas,
bloating, diarrhea. It's also important to drink plenty of water when
eating lots of fiber. Otherwise, you may irritate, even block your
digestive tract.
Nutritionists recommend 20 to 35 grams of fiber a day.
They also recommend that you include both the water-soluble and
water-insoluble fiber in your diet. No problem if you regularly eat a
wide variety of fruits, vegetables and whole-grain breads and cereals.
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