I've heard that powdered cellulose, used in pet food, is actually sawdust. Is this true?

Cellulose is the fibrous part of all plants. Powdered cellulose is a highly purified insoluble fiber ingredient. It is a white powder and is used in bread making. The purpose of powdered cellulose in pet foods is to replace high calorie ingredients in weight loss diets, help promote healthy digestion (it can help with diarrhea or constipation) and control hairballs in cats. Low fat, high fiber diets are often recommended to help control blood sugar levels and prevent pancreatitis in diabetic pets.