Grain allergies are extremely rare in dogs. There's no proven benefit to a grain free diet outside of a legitimate allergy. However, the lack of grains isn't inherently bad like many people seem to believe. The issue is boutique brands pooping up left and right touting grain-free foods to appeal to the masses wanting their fad diet. These companies didn't do their nutritional research (or didn't care about what it says), and took out grains without replacing their nutritional value. This caused a malnutrition issue that has resulted in serious heart disease in dogs eating these diets. Grain free foods that have complete nutrition won't cause heart disease just because they're missing grains.