Here is information about dog food from the nutritionist at the University of Minnesota.

http://www.kare11.com/news/article/962310/26/High-priced-dog-foods-Are-they-worth-the-money

Check for the AAFCO statement and buy a food made for your dog. If it's a puppy, get puppy food and if it's a big dog that exercises a lot go for a higher calorie count. You should also follow the feed directions on the bag.