Soluble fiber consists of nondigestible complex plant carbohydrates that dissolve in water, forming a gel. This type of dietary fiber thickens and slows the movement of chyme through the small intestine, thereby slowing the absorption of glucose into the blood. This may decrease insulin spikes and the risk of type 2 diabetes. Soluble fiber can also help lower blood cholesterol. Good dietary sources of soluble fiber include oats, apples, and beans.
Insoluble fiber consists mainly of cellulose, and does not dissolve in water. As insoluble fiber moves through the large intestine, it stimulates peristalsis. This keeps food wastes moving and helps prevent constipation. Insoluble fiber in the diet may also decrease the risk of colon cancer. Good dietary sources of insoluble fiber include cabbage, bell peppers, and grapes.