Dietary Fiber: Dietary fiber comes from the thick cell walls of plants. It is an indigestible complex carbohydrate. Fiber is divided into two general categories: water-soluble and water-insoluble.
Soluble fiber has been shown to lower cholesterol. However, in many studies, the degree of cholesterol reduction was quite modest.
Diets higher in insoluble fiber (mostly unrelated to cholesterol levels) have been shown to correlate better with protection against heart disease in human trials.
Soluble fibers can also lower blood-sugar levels, and some doctors believe that increasing fiber decreases the body’s need for insulin—a good sign for diabetics.
Insoluble fiber acts as a stool softener, which speeds digestion through the intestinal tract and, for this reason, is an effective treatment for constipation. The reduction in “transit time” has also been thought to partially explain the link between a high-fiber diet and a reduced risk of colon cancer.