Your body does not digest or absorb dietary fiber. However, it plays an essential role in promoting regular bowel movements, reducing cholesterol levels, decreasing your risk of hemorrhoids, diverticulitis, obesity, colon and breast cancer, and improving blood sugar levels in diabetics. Two types of fiber exist: soluble and insoluble fiber. Neither type contains fat, but at least one type contains some calories.
Insoluble Fiber
Insoluble fiber promotes the movement of material through your digestive system and increases stool bulk. It also helps prevent or treat constipation. Insoluble fiber comes from wheat bran, whole grain foods, vegetables, fruits and legumes, such as dried peas, beans and lentils. Components include lignin, cellulose and hemicellulose. Typically, this type of fiber, because it does not become absorbed by the body at all, contains no calories and no fat.
Soluble Fiber
Soluble fiber dissolves in water to form a gel-like material. It can help lower blood cholesterol and glucose levels. Soluble fiber comes from oats, peas, beans, apples, citrus fruits, carrots, barley and psyllium husks from a shrub-like plant called Plantago ovata. Components of soluble fiber include pectin, gum and mucilage. Unlike insoluble fiber, soluble fiber does interact with your body. It binds to bile acids in your intestines helping to eliminate them. Bacteria in your intestines can also ferment fiber producing chemical byproducts which your body uses and which can contain calories.
Calories
In the United States, the Food and Drug Administration does not require manufacturers to include the breakdown of soluble and insoluble fiber in fiber calorie counts on nutrition labels. When labels do list fiber in terms of the food's total carbohydrate content, the standard amount lists 4 calories per gram. For example, popular fiber supplements containing soluble fiber, such as wheat dextrin or hydrolyzed guar gum list about 16 calories per 4 g serving, or about 4 calories per gram. However, according to a 2002 report by the Institute of Medicine, fiber contains about half that amount, or about 1.5 to 2.5 calories per gram. Some of the calories listed may not be a direct result of the fiber itself, but rather due to the action of intestinal bacteria. Bacteria in the large intestines ferment fiber, producing chemicals containing calories the body then uses.
Fat
Neither insoluble nor soluble fiber contains fat, and both can actually decrease your total fat intake. According to MayoClinic.com, fiber-rich diets tend to make you feel full on fewer calories and less fat. High-fiber foods require more chewing time, giving your body time to register the feeling of being full and the bulk of fiber-rich foods increases the volume of your meal, so you stay full for a longer period of time.
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