Cellulose is a carbohydrate that does not change chemically during the human digestive process. Since  cellulose is indigestible, it passes through the intestinal tract unchanged.
Cellulose is present in fiber-containing foods, such as green vegetables, fruits, and whole-grain wheat bread.
Cellulose aids in the elimination of waste products from the intestine, and for this reason, it is sometimes used in the treatment of constipation.