What is fiber?
A variety of definitions of fiber exist. In an attempt to develop one definition of fiber that everyone can use, the Food and Nutrition Board assembled a panel that came up with the following definitions:
- Dietary fiber consists of nondigestible carbohydrates and lignin that are intrinsic and intact in plants. This includes plant nonstarch polysaccharides (for example, cellulose, pectin, gums, hemicellulose, and fibers contained in oat and wheat bran), oligosaccharides, lignin, and some resistant starch.
- Functional fiber consists of isolated, nondigestible carbohydrates that have beneficial physiological effects in humans. This includes nondigestible plant (for example, resistant starch, pectin, and gums), chitin, chitosan, or commercially produced (for example, resistant starch, polydextrose, inulin, and indigestible dextrins) carbohydrates.
- Total fiber is the sum of dietary fiber and functional fiber. It's not important to differentiate between which forms of each of these fibers you are getting in your diet. Your total fiber is what matters.
You may also hear fiber referred to as bulk or roughage. Call it what you want, but always remember that fiber is an essential part of everyone's diet. While fiber does fall under the category of carbohydrates, in comparison, it does not provide the same number of calories, nor is it processed the way that other sources of carbohydrates are.
This difference can be seen among the two categories that fiber is divided into: soluble and insoluble.
- Soluble fiber dissolves in water to form a gel-like substance. Sources of soluble fiber are oats, legumes (beans, peas, and soybeans), apples, bananas, berries, barely, some vegetables, and psylluim.
- Insoluble fiber increases the movement of material through your digestive tract and increases your stool bulk. Sources of insoluble fiber are whole wheat foods, bran, nuts, seeds, and the skin of some fruits and vegetables.