Cat food that is grain-free is just like human grain-free food. It is void of grains. Common grains in cat food include wheat, corn, barley, oats, rice, and gluten. For cats, many of these carbohydrates are very hard to digest. By eliminating the grains and fillers, the food will have fewer chemical additives and be more all-natural cat food. Cats like humans do not need chemical additives in their diets, it is harmful to their health.