What is the natural or original diet for humans? Do any other animals develop food allergies?

I'm not asking for philosophical guessing. This might be a question for those who have more knowledge of veternary science, comparative anatomy or maybe anthropology. From what I know about animals, they don't have food allergies but most have much narrower diets. Are food allergies a product of something different about our immune system? Do other animals have no eosinophylls in their blood?