Nutrition Guidelines & Diets for Dietary Fiber

Fiber is an indigestible complex carbohydrate that is found in the structural components of plants. The fiber content of food is usually expressed as “dietary fiber.” Because it cannot be absorbed by the body, dietary fiber provides no calories; however, the health benefits of eating plenty of dietary fiber are many and significant, including the prevention of constipation, the regulation of blood sugar, and possible protection against heart disease, high cholesterol, and certain forms of cancer. The National Cancer Institute recommends a daily fiber intake for adults of 20-35 grams. The average American adult consumes only 7-8 grams each day. For information and guidelines to help you increase your daily intake of fiber, see the High-Fiber Diet.

Note: When adding high-fiber foods to your diet, be sure to do so gradually -- and to increase your intake of water as well (to at least eight glasses a day) -- in order to avoid digestive discomfort such as diarrhea, and excess intestinal gas.

Types of Fiber

There are two basic types of dietary fiber -- soluble and insoluble. Your diet should include both, because each type of fiber has distinct beneficial functions that can help you to improve or maintain your general health. Soluble fiber, for example, is believed to be beneficial in lowering blood cholesterol and is therefore considered a valuable tool in the management of heart disease. Insoluble fiber is particularly effective in the prevention and treatment of constipation and may also help to reduce the risk of colon and colorectal cancer. (See Low-Fiber (Low-Residue) Nutrition for information on conditions and treatments requiring a diet that is low in fiber.)

The following sections discuss the two kinds of dietary fiber in further detail.

Soluble Fiber

Soluble fiber comes in a variety of forms. Pectin, a complex carbohydrate, is concentrated in the rinds, skins, and/or cores of many fruits (under-ripe fruit contains more pectin than ripe fruit). Food manufacturers use pectin as a thickening agent and stabilizer in candies, syrups, and frozen desserts; it is also used to set jams, jellies, and preserves. Gums and mucilages, which can be found in oatmeal, oat bran, and dried beans, are closely related plant flours that are also used primarily as thickening agents and stabilizers in a variety of foods. (In addition, gums help to prevent the formation of ice crystals in ice cream and other frozen food products, and to retain moisture, which allows foods to remain fresh longer.)

For specific beneficial effects of including soluble fiber in your daily diet and a list of soluble-fiber food sources, see the following sections.

The Benefits of Soluble Fiber

Including soluble fiber (pectin, gums, and mucilages) in your daily diet can be beneficial in a number of ways:

· Reduce Your “Bad” Cholesterol

By including soluble fiber in your diet, you may lower the level of plaque-forming LDL (“bad”) cholesterol in your blood. As soluble fiber passes through the gastrointestinal tract, it binds to bile acids, which are made of cholesterol, and carries them through the intestines, thereby limiting the amount of cholesterol the body absorbs. Soluble fiber is the only food component known to help lower blood cholesterol; however, the degree of possible reduction in your LDL cholesterol level depends on a number factors in addition to your daily intake of soluble fiber: your initial cholesterol level, your weight, whether you smoke, and how much exercise you get. In general, people with high LDL cholesterol levels who add soluble fiber to their daily diet are likely to experience greater reductions than people with lower initial levels. Because of its potential effects on cholesterol level, soluble fiber is considered a valuable tool in the management of heart disease.

· Help Your Digestive System

Soluble fiber is effective in maintaining the proper functioning of the digestive system by promoting regularity, which in turn helps to protect against colon and colorectal cancer, diverticular disease, irritable bowel syndrome, and the development of gallstones.

· Manage Diabetes

When consumed in large amounts, soluble fiber helps in the management of diabetes by slowing the absorption of glucose from the small intestine.

Sources of Soluble Fiber

Soluble fiber is found in the following foods:

· Apples

· Barley

· Dried beans

· Beets

· Carrots

· Cranberries

· Red currants

· Gooseberries

· Grapefruit

· Concord grapes

· Oats (oat bran, oatmeal)

· Oranges

· Peaches

· Pears

· Sour plums

· Prunes

· Psyllium husk

· Quinces

· Rye

· Sesame seeds

Note: Most high-fiber foods are low in fat and provide a variety of other nutrients, such as antioxidants and vitamins, that may help to protect against cancer, heart disease, and other serious health conditions.

Insoluble Fiber

Cellulose, hemicellulose, and lignin are all types of insoluble fiber. Cellulose, which is found in apples, beets, broccoli, pears, and whole grains, helps to nourish blood vessels and to cleanse the intestinal tract. Hemicellulose (which is also considered a soluble fiber) helps to move waste through the body by absorbing water in the intestinal tract; it is found in apples, beets, cabbage, corn, peas, and whole grains. Lignin, the least digestible of the different types of fiber, is an effective antioxidant and is found in carrots, green beans, potatoes, tomatoes, whole grains, and many other foods.

For specific beneficial effects of including insoluble fiber in your daily diet and a list of insoluble-fiber food sources, see the following sections.

The Benefits of Insoluble Fiber

Including insoluble fiber (cellulose, hemicellulose, and lignin) in your daily diet can be beneficial in a number of ways:

· Bulk Up

Foods that are rich in insoluble fiber are commonly referred to as “roughage,” because insoluble fiber is indigestible and increases bulk in the intestines as it absorbs water. Bulk helps to maintain the proper functioning of the intestines by keeping bowels regular and, in turn, preventing constipation. Because insoluble fiber speeds the movement of potentially carcinogenic substances through the digestive system, it also helps to reduce the risk of colon and colorectal cancer. In addition, by softening stools, insoluble fiber may help to prevent hemorrhoids and diverticular disease.

· Watch Your Weight

A diet that is high in insoluble fiber and low in fat may help with weight control. The bulk that is created in the intestines as insoluble fiber absorbs water can reduce your appetite by making you feel full faster.

· Manage Diabetes

Like soluble fiber, insoluble fiber helps in the management of diabetes by slowing the rate at which your body absorbs glucose.

Sources of Insoluble Fiber

Insoluble fiber is found in the following foods:

· Brazil nuts

· Whole-grain breads and cereals

· Fruits and vegetables with skins

· Peanuts

· Popcorn

· Brown rice

· Wheat bran

Low-Fiber (Low-Residue) Nutrition

Although a healthy body requires a diet that includes both soluble and insoluble fiber, some specific health conditions and treatments require a low-fiber, or low-residue, diet. (“Residue,” which is used as a synonym for fiber, refers specifically to food material that remains in the intestines after digestion and absorption.) By reducing the frequency of bowel movements and helping to prevent irritation in the gastrointestinal tract, a low-fiber diet can be very beneficial for people with diarrhea and/or abdominal cramping, and for those who are experiencing or have recently experienced acute phases of ulcerative colitis , regional enteritis (Crohn’s disease , or diverticulitis . (A high-fiber diet can be helpful in preventing the inflammation that leads to diverticulitis, but a diet that is low in fiber is required during the period of inflammation to minimize residue and fecal volume.) A low-fiber diet may also be used postoperatively -- following a hemorrhoidectomy or large bowel surgery, for example -- to minimize residue and fecal volume as a patient gradually returns to a regular diet. People experiencing rectal bleeding, partial intestinal obstruction, or constriction of the esophageal or intestinal passageways may also benefit from a low-fiber diet for short periods of time. See the Low-Fiber Diet for further information and specific guidelines.

Fiber Content of Foods

To view tables showing the fiber content of various foods, click here: http://www.slrhc.org/healthinfo/dietaryfiber/fibercontentchart.html target=”blank”>Fiber Content of Foods</a>.

For related information, consult the following links:

Dietary & Behavioral Tips for Constipation

Preventing and Treating Constipation During Pregnancy

Food Labels

High-Fiber Diet

Low-Fiber Diet

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