Nutrition and Health Info Sheet: Fiber

Abstract

SOME fACTS ABOUT FIBER What is fiber? Multiple definitions of total fiber are recognized; however, the most recently accepted definition considers it the sum of dietary fiber and functional fiber. Dietary fiber, also called roughage, bulk, and viscous fiber, includes nondigestible carbohydrates and lignin most commonly found in plants. Functional fiber is defined as isolated, manufactured , or synthetic oligosaccharides with three or more degrees of polymerization, and it is found in both plants and animal products. Fiber plays an important role in several physiological functions and has beneficial effects on laxation, blood glucose, and cholesterol concentrations. 1 Fiber has also been implicated in reducing the incidence of diverticulosis, cardiovascular disease, and some cancers. 1,2 What is the difference between soluble (viscous) and insoluble fiber? Historically, fiber has been classified as soluble (gums, mucilages, and pectins), now referred to as viscous, and insoluble (cellulose, hemicellulose, and lignin). These classifications were intended to predict physiological outcomes but this has been increasingly questioned by further studies. 4 The United Nations, in a joint FAO/WHO report, proposed that these terms be phased out, but nutritionists continue to rely on them heavily. 5 What are good sources of fiber? Whole grain products, vegetables, and fruits are the principal sources of fiber in our diet. According to the U.S. Food and Drug Administration (FDA) label content laws, the term high fiber indicates a food that has at least 20 percent of the Adequate Intake (AI) for fiber, and a good source of fiber food must have between 10 and 15 percent of the AI for fiber. 6 There is no fiber in meat, fish, eggs, milk, or cheese. Grain products Whole grain flour and foods made from whole grains contribute the greatest amount of fiber in the diet compared with other food sources. Rye is highest on the list, followed by wheat, barley, oats, brown rice, and corn meal. Bran (the outer layer of the grain kernel) contains most of the fiber in a grain (up to 90 percent, depending on how it is processed). Vegetables Legumes (dried beans, peas, and lentils) are the highest source of total fiber among vegetable sources. Potatoes, carrots, cabbage, and tomatoes have lower fiber content, but they often contribute more fiber to our daily diet because we eat them more frequently. Vegetables tend to have less fiber than cereals because they are higher in water content. Fruit Raspberries, apples, and oranges provide a good source of fiber.