Hi Kirstie, The main source of carbohydrates in any dog food depends on each recipe. For most kibbles, itâs typically a cereal grain (corn, wheat, rice, barley, etc.), potatoes or legumes (peas or beans). The only reasonable function for carbs is to supply energy (calories) to the animal.he fact that a dog food doesnât need to contain any âcarbsâ at all seems hard to believe. But itâs true. You see, according to the National Research Council and compared to the other two major nutrients â protein and fat â no carbs are considered essential for a healthy canine diet. Dogs donât need corn.