While we can't digest fiber, friendly bacteria in the colon ferment some types of fibers. This action creates substances called short chain fatty acids that help keep the intestinal walls healthy. It also causes the formation of intestinal gas. Fiber found in the food you eat is defined as dietary fiber. Functional fiber has been isolated, extracted or manufactured. This type of fiber is used as a dietary supplement or added nutritional ingredient in some foods. The components of dietary fiber include cellulose, lignin, pectin, chitan, beta-glucan and oligosaccharides and there are two general categories of fiber, insoluble and soluble.
Insoluble Fiber and Soluble Fiber
Insoluble fiber is found in whole grains, nuts, wheat bran and vegetables. This type of fiber does not dissolve in water so it helps move material through the colon faster by increasing the bulk of the stool. This can be helpful to people who suffer from constipation or irregularity. Diets high in insoluble fiber may also decrease the risk of diabetes. Soluble fiber is found in oats, citrus fruits, apples, barley, psyllium, flax seeds and beans. Soluble fiber dissolves in water, which helps soften stools, making them easier to eliminate from the body. Soluble fibers called beta-glucan bind to the bile acids that contain cholesterol. So eating a diet high in this type of soluble fiber has been shown to reduce cholesterol.Types of Fiber
The components of fiber include cellulose, hemicellulose, lignin, pectin, chitin, gums, beta-glucan, and resistant starches.Cellulose and Hemicellulose
Cellulose is an insoluble dietary fiber and may also be used as a functional fiber. Celluloses are long straight chains of glucose molecules and are found as the main component in cell walls of plants. The bacteria in your intestinal tract cannot ferment cellulose well either, so the main function of cellulose is to increase stool bulk and decrease the time it takes for fecal material to pass through the colon. Foods that contain large amounts of cellulose include bran, legumes, nuts, peas, roots, cabbage and apple skins.
Hemicellulose is found in bran, nuts, legumes and whole grains. This form of fiber is also found in the cell walls of plants, however hemicellulose may be made of several types of sugar. Rather than just long straight chains like cellulose, hemicellulose may have side chains and branches. Because of these variations, some hemicelluloses are soluble in water and some are insoluble, plus some forms are fermented by bacteria while others are not.
Lignin
Lignin is a type of fiber with lots of branches of chemicals called phenols rather than sugar molecules. Phenols are currently being studied for a variety of health-related effects including antioxidant actions. Lignin is insoluble in water and indigestible by the friendly bacteria. Food sources include root vegetables, wheat and within berries' seeds.
Pectin
If you have ever made jams or jellies at home, you have probably used pectin to help your fruit gel. Pectin is another type of fiber found in the cell walls of plants that is soluble in water. But it doesn’t make a good stool-bulking agent because it is a favorite fiber for the friendly bacteria in your gut to ferment so that very little passes through the colon. Pectin is found in apples, legumes, nuts and citrus fruits.
Chitin
Chitin is similar to cellulose because it is insoluble in water and made up of glucose chains, but it also has amino acids attached. Chitin is interesting because this fiber is found not only in plants but also in the exoskeletons of insects and in the shells of crustaceans.
Gums
Gums are soluble in water and plants secrete gum when they are damaged. A variety of types of sugars are found in the structures of gums. They are used in food manufacturing as thickening and gelling agents. Examples of gums include guar gum, carob gum, gum Arabic and xanthan gum.
Beta-glucans
Beta-glucan is a water-soluble dietary fiber found in oats and barley and it is often used as a functional fiber and added to foods. Beta-glucans have been shown to reduce cholesterol levels and help control blood-sugar levels.
Resistant Starches
Resistant starch is really starch, but is considered to be a fiber because amylase, the enzyme that breaks starch into individual glucose units, doesn’t work on this type of starch. Resistant starch can occur naturally as starch trapped in cell walls of plants or may be formed during cooking or food processing.
