It seems that his problem was burning off everything he would eat very rapidly. Not unusual for a very active teenager, heck he was and athlete long before he was an actor and the metabolism comes with the territory. As far as what he ate, it seems that really didn't matter as much as the frequency of the mini-meals. Action Fuel Pro
As for his workout he did a very basics workout with weight lifting, endurance training and abdominal work. The key was the intensity of the routine and the amount of weight couple d with resistance.