The term "roughage" is an umbrella term for the different types of fiber, one of which is cellulose. Fiber is found in plant foods only, and different types of plant foods contain different types of fiber. An adequate fiber intake confers many health benefits, and is also a useful weapon in the weight-loss arsenal. The Dietary Reference Intake of fiber is 38 g per day for men and 25 g per day for women, and many foods can help you meet your needs.
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The human stomach lacks the enzymes necessary to digest fiber, so although it may be slightly processed in the intestines, it passes through mostly untouched. Fiber may be insoluble, like cellulose, or soluble, like pectin. Soluble fiber binds to water during digestion, causing the food to move more slowly through the digestive tract, making you feel full longer. Insoluble fiber adds bulk to the stool, promoting rapid transit and stimulating bowel movements. Both types of fiber are vital to good health.
Because insoluble fiber improves stool transit time, including it in your diet may relieve chronic constipation and soften hard stools -- on the other hand, its bulking action can help firm loose stools. This bowel normalization can help prevent hemorrhoids and other intestinal complaints, and may help relieve symptoms of irritable bowel syndrome. There are theories that insoluble fiber may help reduce your risk of colorectal cancer because it keeps potential carcinogens from sitting in the colon long enough to cause problems, but according to MayoClinic.com, more study is needed.
Soluble fiber may help control blood sugar by slowing the rate at which sugar is absorbed into the bloodstream. It may also help lower cholesterol levels by increasing the amount of cholesterol you excrete, but the mechanism is still sketchy -- according to Colorado State University Extension, oat fiber and pectin have been found more effective at lowering cholesterol than wheat fiber, and the reason isn't clear. Fiber of any type can improve cardiovascular health by helping to lower blood pressure and reduce inflammation.
Legumes and vegetables contain both soluble and insoluble fiber -- insoluble fiber, like cellulose, forms the walls of the plant cell, while soluble fiber is found inside the cell. The fiber in fruit is mostly soluble, while the fiber in whole grains is mostly insoluble. When the bran is isolated from the whole oat, it contains mostly soluble fiber -- oat bran is sold as a separate ingredient that can be added to bread dough or sprinkled on top of cereal or yogurt. Processing destroys the fiber content of most foods, so choose the form closest to the natural state -- eat an apple instead of drinking apple juice, for example. Fiber foods have a low energy density, take longer to chew and keep you full longer, so may be especially helpful during weight loss.