by-products are less biologically available than actuall flesh so if your going to pay high prices for cat food ,in my opinion, your better off looking for foods without byproducts and without chemical preservatives. the higher quality foods have more usable nutrients(contributing to less waste) and thats why your cat will actually eat less of a higher quality brand than a lower quality brand. for example one 18lb bag of cat chow used to cost me around $12 and last for about a month for my 3cats and then i switched them to solid gold and i only went through 8lbs in a month. they definatly poop less than they did also. in my opinion, solid gold, innova, wellness, felidae are super high quality brands.