Adequate daily intake of dietary fiber helps to prevent constipation and diverticulosis. In addition, eating a diet rich in fiber from whole grains is associated with a decreased risk of heart disease. It appears that optimal physiological functioning of the intestinal tract is dependent upon a satisfactory mixture and level of dietary fiber.
Dietary fiber is the total amount of undigested, naturally occurring material in foods. It is a complex carbohydrate found in all plant-based foods — including fruits, vegetables, grains, breads and cereals. Fiber is not found in meat, milk, cheese or oils, and the refining process used to make white flour removes almost all of the fiber from grains. Because fiber is not digested and absorbed, its importance lies in what it does as it passes through the body.
There are six main types of fiber:
- Cellulose is the structural fiber in plant-cell walls found in all fruits, vegetables and legumes.
- Hemicellulose is the main structural fiber in cereals.
- Lignin is the only non-carbohydrate fiber and is the toughest of the fibers, found in small fruit seeds (such as raspberry or strawberry seeds) or in the woody parts of vegetables (such as carrots).
- Pectin, which forms a gel when combined with water, is found in high quantities in apples and citrus fruits, but can be found in most fruits and vegetables.
- Gums are the sappy substances exuded by plants. They often are used as food additives for thickening.
- Mucilages are similar to gums and are used as stabilizers in prepared foods.
These types of fiber differ in ability to hold water, solubility and viscosity, and ability to bind with other substances such as minerals and bile. The most popular way of grouping the fibers is by solubility.
Soluble fibers — gums, pectins, mucilages and some hemicelluloses — dissolve in water and are abundant in fruits, legumes, barley and oats. Soluble fibers slow down stomach-emptying time, which allows you to feel fuller longer and gives your digestive system more time to absorb nutrients from the foods you eat. Soluble fibers also bind with bile in your intestines and carry it out of your body. Since bile is made of cholesterol, that means more harmful cholesterol is leaving your body, which lowers your cholesterol level.
Insoluble fibers — cellulose, lignins and many hemicelluloses — do not dissolve in water. They are found in vegetables, whole-grain breads and whole-grain cereals. Insoluble fibers increase the bulk of stool, making it easier to pass and better able to carry the bound bile out of your system. Insoluble fibers also hasten "transit time," or the speed at which food moves through your gastrointestinal system, which allows the body to rid itself of potentially toxic or disease-causing substances.
Ideally, everyone should get between 20 and 35 grams of fiber each day — about twice as much as the average American consumes. A good place to begin is by following the new Healthy Eatinig Plate. Switch from refined foods to whole-grain foods, which includes changing from white bread to whole-wheat bread and from white rice to brown rice. Besides whole-grain products, other sources of fiber are legumes, lentils, bran, and most fruits and vegetables.
If you decide to increase the amount of fiber you eat, there are some guidelines to remember:
- Since fiber absorbs water, increase the amount of fluids you drink as you increase your fiber intake. Water, juice, broth or low-fat milk are good choices.
- Introduce extra fiber gradually. This will give your body a chance to adjust for the additional gassiness the fiber may cause.
- Eat a variety of plant foods. This will ensure that you get both soluble and insoluble fiber in your diet.
Return to | Diet and GI Health