Cellulose fiber is a type of dietary fiber found in plant cell walls. It is a complex carbohydrate made up of long chains of glucose molecules. Cellulose fiber is not digestible by humans, but it is beneficial for digestion and overall health. It helps to add bulk to the stool, which can help to prevent constipation and other digestive issues. It also helps to slow down the absorption of sugar in the bloodstream, which can help to regulate blood sugar levels.