Do I have to use food to train my dog?

Of course, you don't have to use any particular tool to train your dog. Food is popular because it is one of the most powerful motivators in animal training. The reality is that you get more strongly conditioned behaviors if you do not limit yourself to praise alone. Training with positive reinforcement allows the dog to relax and learn and strenghtens the bond between you and the dog. Over time, you will be able to expect "more for our money," that is more behaviors for fewer treats. You will also become skillful at incorporating other rewards into training.