By reading about it, talking about it, and witnessing the effects of different foods. I do not think I'm an 'expert', but I feel I have much more knowledge than the average pet owner. When I was researching where to get my golden retriever, I stumbled upon a document called, "How to feed your Golden Retriever". From there, I did further research on my own and bought a book called, "Pet Allergies". Then, I did research on different foods and their ingredients. And, it continues from there.