Grains are not a natural food for dogs, even though they are the main ingredient in kibble. It is not something they would eat in the wild. Grains are also one of the major causes of allergies in dogs, as well as flatulence (gas). They are full of carbohydrates which can be easily converted to sugars. Cancer cells feed on sugars and it is believed that by decreasing the amount of carbohydrate in the diet, we may greatly reduce the risk of cancer, which is a growing problem among modern dogs.