Actually the stomach does little to digest any certain food over any other. The most important parts of breaking down the food takes place in the mouth and intestines. Enzymes are designed to break down certain types of food material into a simpler form that can be absorbed into the blood. For example there is a enzyme in human saliva which breaks down carbs into simple sugars. Try it! Find a soup cracker and chew without swallowing for a while, it should become sweet. The body of most animals can determine if a food material is edible and will try to expel it if it not. If it is not removed via vomiting, it will simply be passed in fecal matter. The nutrient content of the food will be intact (the animal cannot receive energy and nutrients from indigestible food as it can't be absorbed into the blood)