I've just read a very useful summary of the pros and cons of using food as the reward in training dogs. I followed a link that Honey the Great Dane sent me. (Well, her human, Hsin-Yi actually sent it to me, but I'm sure Honey was behind it all.)
It's one of the best summaries of the issue I've ever seen.
What I particularly liked was the point that the human has to follow up with the teaching throughout the dog's life. So, if you like jerking on a chain and releasing it, you'll be doing it right through the dog's life. (Definitely not my choice.)
Or, if you reward with food, you are committed to doing that indefinitely. Not all the time, but indefinitely.
And you have to remember that the more treats you give, the less food there will be at mealtimes, or you'll end up with an overfed dog.