The types of dietary fiber found in plant foods are generally classified as either "soluble," which simply means they dissolve in the fluids found in your digestive tract, or "insoluble," which means they do not dissolve. Each type of fiber plays a distinct role in your health. Most food sources of fiber contain both the soluble and insoluble forms, but are higher in one type than the other.
Sources of Soluble Fiber
Oranges, grapefruit, pears, prunes, Brussels sprouts and legumes -- such as lima beans, kidney beans and black beans -- are especially good food sources of soluble fiber. Barley, oatmeal, oat bran, apples, bananas, blackberries, nectarines, peaches, broccoli, carrots, lentils and chickpeas are also good sources. Ground psyllium seeds, available in health-food stores and in some commercially prepared fiber supplements, contain more soluble fiber than any food source.
Sources of Insoluble Fiber
Whole-grain foods, nuts, vegetables and legumes, such as dried beans, are all good sources of insoluble fiber. These groups include whole-wheat breads and other baked goods made with whole-grain flours, wheat and wheat bran cereals, wheat bran, cabbage, cauliflower and turnips. Although the flesh of an apple is particularly high in soluble fiber, apple skin is high in insoluble fiber.
Fiber Benefits
Soluble fiber slows down the movement of food through your digestive tract, allowing time for some nutrients to be absorbed more effectively, which stabilizes blood sugar and promotes normal appetite. The soluble fiber in oats and oat bran stands out from the fiber found in other grains, because it interferes with cholesterol absorption from your intestine, potentially lowering your blood cholesterol levels and protecting your heart. Insoluble fiber speeds up the movement of food through the intestinal tract, which is why it is best known for preventing and relieving constipation. According the American Heart Association, insoluble fiber also helps protect your heart and can slow down the progression of existing heart disease. To get all the benefits of both types of fiber, include a variety of soluble and insoluble fiber sources in your diet every day.
Fiber in Food Labeling
The wording on a food label may indicate that the product contains whole grains or oat bran, but that does not necessarily mean the food is high in fiber. Check the nutrition facts label for the actual fiber levels in one serving of any food. For food labeling purposes, a food that is called a "good source of fiber" contains from 2.5 to 4.9 g of fiber, and a food that is called "high in fiber" must contain at least 5 g. A food label that makes a statement relating soluble fiber to coronary heart disease must also be low in fat, saturated fat and cholesterol.
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