|Types of Dietary Fiber: Water Soluble Fiber; Soluble Fiber; Water Insoluble Fiber; Insoluble Fiber; Pectins; Gums; Mucilages|
|What is it?|
Given all the media hype about fiber, you'd assume it was a
You'd be wrong. Although classified as a CARBOHYDRATE,
fiber supplies no VITAMINS,
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, more
simply, soluble fiber) and those that don't (water-insoluble or insoluble
fiber). The water-soluble fibers —
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 (the liver synthesizes these out of CHOLESTEROL),
and as the acids are bound, cholesterol is withdrawn from the blood and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
levels. And that's good news for diabetics. Intricately bound to
digestible carbohydrates, which the body breaks down to form glucose,
fiber acts like a brake, slowing 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.
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.
What is Insoluble Fiber?
Insoluble fibers absorb and retain water, accelerate the transit time of gastrointestinal contents and thus help to prevent constipation. Water-insoluble fibers include:
Cellulose and hemicellulose are substrates for microbial fermentation, which not only provides energy, but may also be important in converting toxic or carcinogenic compounds into non-toxic forms. These fibers also increase stool bulk, which helps with muscle tone in the colon and makes it less susceptible to the bulging out-pouches seen in diverticular disease. Lignin binds bile acids, which are important in the absorption of cholesterol from food and thus helps in lowering blood cholesterol levels.
What is Soluble Fiber?
Water-soluble fibers include:
Pectins and gums form gels when mixed with water, making the contents more viscous so that food stays in the digestive tract longer. This is important for people who suffer from dumping syndrome after stomach surgery (nausea, weakness, and diarrhea when food moves out of the stomach too rapidly). Soluble fibers also help to delay the absorption of glucose, which is useful in diabetes control, and help to lower blood cholesterol by binding bile acids. The following (partial list of) foods contain soluble fiber:
how much fiber is enough? There is no RDA
for fiber, but most nutritionists recommend 20 to 35 grams of fiber a day
(most Americans get no more than 10 to 13 grams). 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.