Hi Patricia,
If you learned that corn was an empty filler then I’m afraid you have been misled, which is understandable, given the marketing tactics commonly deployed in regards to selling pet foods.
Perhaps the shortest answer to the question is to say that veterinary nutritionists, when formulating foods, determine which nutrients they want to deliver and which need to be controlled and then choose ingredients and how they work together to accomplish that goal. The ingredients are simply a mechanism to achieve a certain nutrient profile.
