Final answer:
Fiber is a carbohydrate that is not digested or absorbed, but it provides many important functions in the digestive system.
Step-by-step explanation:
Fiber is a carbohydrate that travels through the digestive tract but is not digested or absorbed. Fiber supplies no energy. It occurs in roots, stems, leaves, nuts, and seed coverings of vegetables, fruits, and whole grains. Fiber provides bulk for muscles of the digestive tract to squeeze against. This squeezing helps speed the passage of food through the food tube. Fiber also acts like a sponge by holding onto unhealthy substances in food to prevent them from being absorbed into the body. One example of an unhealthy substance is cholesterol. Fiber reduces the absorption of cholesterol into the bloodstream and lowers the chances of getting colon cancer.