Fiber (frequently also called roughage) is a nonnutritious material found in food which is not broken down by the enzymes in the digestive tract. Fiber was once thought to have no food value as such but is now recognized to be an important constituent in the diet. High-fiber diets are sometimes useful in controlling constipation and diarrhea, and are also prescribed for persons with diverticulitis and irritable bowel movement.
Food fibers are divided into two groups: nonabsorbent and absorbent. Nonabsorbent fibers increase the bulk and liquid content of the feces, making them softer and easier to pass through intestines. This type of fiber may decrease the risk of colon cancer because it reduces the absorption of cancer-causing agents and reduces the amount of time these agents remain in the digestive system. Because the passage of feces is easier, less strain is placed on the intestines, diminishing the risk of developing hemorrhoids. Nonabsorbent fibers can be found in whole grains, legumes and in many types of fruits and vegetables.
Absorbent fibers absorb water during the passage through the stomach and the intestine. They may curb the appetite by producing a feeling of fullness and also slow the absorption of food by the digestive tract. In this way, cholesterol levels may be reduced-and the risk of heart disease lowered. These fibers may be found in oats, legumes and a variety of fruits and vegetables. When switching to a high fiber diet, it is important to increase the consumption of fiber gradually-to minimize flatulence and bloating-and to drink plenty of liquids to avoid constipation. If certain fibrous foods are difficult to digest, they should be eliminated from the diet and replaced by others.
