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Dietary Fiber

Definition

Dietary fiber (also know as "roughage" or "bulk") is the part of the food that is indigestible. Found only in plant foods, it moves largely unaltered through the stomach and small intestine and into the colon.

Description

There are two types of dietary fiber: insoluble and soluble.

Insoluble fiber does not dissolve in water and travels through the small intestines quickly. Wheat bran, whole grains breads and cereals, as well as the skins of many fruits and vegetables are considered insoluble.

Soluble fiber breaks down as it passes through the digestive tract forming a gel that traps some substances that are beneficial in lowering cholesterol, stabilizing blood sugar and affecting nutrient absorption. Examples of soluble fibers are oats, beans, barley, and many fruits and vegetables.

Benefits Of Fiber

Fiber has at least two well-known benefits:

• It prevents and relieves constipation by stimulating movement of your intestinal muscles, increasing stool bulk and making your stools softer and easier to pass.
• It helps to control weight by creating a feeling of fullness without adding too many calories to the diet.

Additionally, dietary fiber may reduce the risk of many other health conditions, including:

• Gastrointestinal disorders. By avoiding constipation, one reduces the risk of developing hemorrhoids (swollen anal tissues), diverticulosis (pouches that protrude through weak spots in the colon), and irritable bowel syndrome (muscle spasms in the stomach walls).
• Elevated cholesterol. Soluble fiber binds with certain digestive acids made from cholesterol in the liver, and then takes the acids away in the stool. In response, your liver draws cholesterol from your blood to make more acids, thus lowering your blood cholesterol.
• Diabetes. Soluble fiber slows absorption of blood sugar from the small intestine, making sugar levels easier to control.
• Colon Cancer. Insoluble fiber minimizes exposure to carcinogens that may be in the stool by diluting them and speeding their transit through the bowel. Additionally, the insoluble fiber reduces bile acids and certain bacterial enzymes that may promote the growth of precancerous polyps (tissue growths that protrude from a membrane such as the intestinal lining) and colon cancer. While not definitively proven, intake of fiber may protect against the development of colon cancer.
• Breast Cancer. Fiber helps speed cancerous substances that have reached the intestines through and out the body before they can cause serious damage. Women who eat extra fiber also rid themselves of more of their excess estrogen in bowel movements rather than in urine. This is important because estrogen in the urine can be reabsorbed into the blood stream and eventually reach the breasts and other organs vulnerable to hormone-related cancer. Dietary fiber "binds up" estrogen as it enters the small intestine and may do the same with other cancer-causing agents, preventing them from being absorbed.

Overall, the strongest evidence of a major reduction in risk comes from studies of diets that are rich in high fiber foods, not just in fiber alone. Such foods, low in fat and rich in nutrients, have many health benefits beyond those provided by fiber.

Recommended Daily Allowance Of Fiber

The Dietary Guidelines for Americans published jointly by the U.S. Departments of Agriculture and Health and Human Services recommends eating foods that have adequate amounts of fiber, and one organization, the National Cancer Institute, recommends 20 to 30 grams of fiber per day with an upper limit of 35 grams. Americans typically consume 10 to 15 grams of fiber a day.

Consuming the following recommended servings of a variety of fruits, vegetables, and grains throughout the day should bring the intake within the range recommended by the National Cancer Institute and the U.S. Department of Agriculture.

Fruits (2 to 4 servings per day)

Apple - 1 medium

Banana - 1 medium

Orange - 1 medium

Vegetables (3 to 5 servings per day)

Peas - 1/2 cup

Potatoes (with skin) - 1 medium

Corn - 1/2 cup

Green beans - 1/2 cup

Grains (6 to 11 servings per day)

Oatmeal (cooked) - 3/4 cup

White rice - 1/2 cup

Wheat bread - 1 slice

100% Bran - 1/2 cup

The more insoluble fibers such as those found in wheat bran have the greatest effect on colonic function.

Soluble fibers such as those found in legumes, oats, and fruit result in lower blood sugar levels in diabetics and lower blood cholesterol.

Note: Fiber needs fluid to be effective, so it's important to drink about 64 ounces of water daily.

Side Effects

It's important to adjust fiber intake gradually over a period of one to two weeks. This will give the stomach and intestines time to adjust to the dietary change. It will also minimize problems such as diarrhea, bloating or gas that can result when too much fiber is consumed.

Moderation is particularly important for older people because their bowel function may be sluggish.

Because fiber substances can bind divalent cations, it has been feared that high-fiber diets could lead to deficiencies of calcium and zinc, among other minerals. Current evidence suggests that moderate fiber intake will not cause nutrient deficiencies.

Fiber Supplements

Fiber supplements (such as Citrucel, FiberCon, GenFiber, Hydrocil and Metamucil) should be used only on the recommendation of the doctor.

Taken properly, they may help with constipation, cholesterol levels or intolerance to high-fiber foods, but their anticancer benefit is questionable.

Relying on fiber supplements is generally unwise because they do not contain the many essential nutrients found in high-fiber foods.

Questions to Ask Your Doctor

How do you know if more fiber is needed in the diet?

What if a person is allergic to whole grain foods?

Should a nutritionist be consulted in regards to changing the current diet?

Are there signs and symptoms to watch with respect to eating too much fiber?

What is your opinion regarding fiber supplements?