Some foods contain fiber, which is a tough complex carbohydrate. Fiber may be
Partly soluble: It dissolves in water, and the body may be able to digest some of it.
Insoluble: It does not dissolve in water, and the body cannot digest it.
Fiber in the diet helps mainly by adding bulk to the contents of the intestines. This helps make stool easier to pass and minimizes constipation. Fiber also may provide satiety (the feeling of fullness and relief of hunger). However, eating too much insoluble fiber can make you feel bloated and also interfere with absorption of certain vitamins and minerals.
Authorities generally recommend that about 30 grams of fiber be consumed daily. In the United States, the average amount of fiber consumed daily is about 12 grams because people tend to eat products made with highly refined wheat flour and do not eat many fruits and vegetables. An average serving of fruit, a vegetable, or cereal contains 2 to 4 grams of fiber. Meat and dairy foods do not contain fiber.
Comparing Soluble and Insoluble Fiber
Type of Fiber | Sources | Functions |
|---|---|---|
Soluble | Apples (mainly in the flesh of the apple) Barley Beans Citrus fruits Lentils Oat bran Oatmeal Pectin (from fruit) Psyllium Rice bran Strawberries | Helps moderate the changes in blood sugar and insulin levels that occur after eating a meal Helps reduce cholesterol levels May reduce the risk of atherosclerosis (including coronary artery disease) |
Insoluble | Apples (mainly in the skin of the apple) Brown rice Pears Prunes Many vegetables, including cabbage, root vegetables, and zucchini Whole grains and whole-grain breads and pastas | Provides bulk to feces and thus helps food move through the digestive tract, preventing constipation Helps eliminate cancer-causing substances produced by the bacteria in the large intestine Reduces pressure in the intestine, helping prevent diverticular disease Makes people feel less hungry because it adds bulk to the diet, makes people chew more slowly, and keeps food in the stomach longer—and is thus helpful in losing weight |
