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.
Eating too much insoluble fiber can 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
Pectin (from fruit)
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)
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
In commercially prepared foods, the amount of additives that can be included is limited to the amounts shown to be safe by laboratory tests. However, weighing the benefits of additives against the risks is often complex. Which of the following additives has been shown to convert to a substance that can cause cancer in animals?