If you want to learn a lot about dog nutrition, here is a link to a site that is run by a veterinary nutritionist. You can find her resume on that website. She has an extensive library in her FAQs...if you don't find the information you need there, you can send her an email and she will respond! Be very careful about some of the websites that rank dog foods....many of them are run by people with no animal nutrition backgrounds at all. There is one in particular who ranks food by ingredients...I won't say that ingredients are not important; but quality control is, in my opinion, the very first thing to look at. There have been SO many recalls and in the past many pets have died because of a lack of quality control.
As others have said, the best food is that which works for your pup.
www.petdiets.com