When planning your cat’s diet, you’re not limited to what you can buy in cans and packages. While many—if not most—human foods should not be fed to cats, some are absolutely wonderful.
Oats, for example, have a lot of protein per calorie, and they’re easy to make. Also, many cats like corn and polenta, a coarsely ground cornmeal, has a good texture for them. You can try brown rice, barley, and wheat berries, but you may need to mash them. Cats tend to like smaller grains like millet and couscous.
Make sure any grains are cooked so your kitty can digest them fully. Whole wheat bread crumbs are OK, too.