The dog's diet among other things (exercise) are so important for a healthy dog. Unfortunetly the main stream dog foods are of very poor quality (Iams,Ol`roy, Science Diet, Pedigree etc). These foods use very low quality meat (if any), use a ton of fillers, some of these companies also use very unethical ways of testing their food on animals.
Good information on dog food is
http://www.dogfoodanalysis.com/http://www.whole-dog-journal.com/You can obtain a journal from whole-dog that have all the recommended kibbles (also contains the non-recommended ones). The whole dog journal is a great source of information for information high quality diet, (kibble and canned food), dog/owner psychology and training.
The one thing to note is that if you are interested in feeding your dog a high quality diet you might need to find a speciality dog food store depending in your area because the big name brand stores do not carry the really good high quality dog food.
