Fiber is an important component in any healthy diet that helps ensure digestive tract health. Insoluble fiber is one type of dietary fiber found in foods, and it is made up of a few different plant compounds. Healthy adults should consume between 25 to 38g of fiber every day and this should be a combination of fiber types from a variety of whole foods sources.
Definition
Insoluble fiber is considered any fiber that does not dissolve in water, in contrast to soluble fiber, which does. All fiber passes through the start of the digestive tract intact, but may be handled differently by the body once it reaches the large intestines. According to World's Healthiest Foods, many researchers and medical professionals find that the current classifications of soluble and insoluble fiber are insufficient, so other ways of defining fiber, such as based on its fermentability or source of origin, have been proposed.
Types
One type of insoluble fiber found in food is cellulose, a carbohydrate component of plant cell walls. Lignins are another type of insoluble fiber that occurs in the cell walls of woody plants and seeds. Some pectins, polysaccharides found in fruits and berries, are also insoluble. The group hemicelluloses, another type of carbohydrate found in all plant cell walls, contains some members that are insoluble and some that are soluble.
Sources
Many sources of fiber contain both insoluble fiber and soluble fiber together, but the proportions may vary. A half cup of 100 percent wheat bran cereal contains 12.5g of fiber, which is mainly composed of cellulose and hemicellulose, both of which are insoluble fiber. Hemicellulose is also found in high amounts in other whole-grain cereals. Cellulose occurs in apples, legumes, root vegetables and the outer covering of edible seeds. Root vegetables and fruits with edible seeds such as strawberries are good sources of the insoluble fiber lignin.
Benefits
One of the main benefits of insoluble fiber is the promotion of bowel health. Insoluble fiber bulks up stool as it passes through the intestines and speeds up the passage of stool through the intestinal tract. Because of its contribution to bowel regularity, insoluble fiber may be responsible for a reduced risk of colon cancer, hemorrhoids and diverticulosis.
Considerations
In general, the consumption of whole foods is required for adequate consumption of insoluble fiber. Juices and processed foods often have at least some portion of the fiber removed. If you have had a low intake of fiber, it's a good idea to build up your consumption gradually instead of increasing your fiber intake suddenly, since this could lead to bloating and gas. Fiber intake should also be balanced with an increase in water consumption.
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