Extra fiber. You see it in large friendly letters on cereal boxes, orange juice cartons, everything, but you probably wouldn't touch the box if you saw the word "sawdust." From crackers to cocoa mix, cellulose (a.k.a. wood pulp) is used as filler in everyday foods. While the FDA deems wood pulp safe for consumption, the USDA limits cellulose to 3.5% of the total food mass. Maybe it's time to go on that paleo diet.