the problem I see with the Zone is that it teaches you to be a slave to food instead of YOU controlling it. Forget the ins and outs of the types of food to eat yadda yadda yadda and think about portion control to the point where you almost forget how to manage food and worry about controlling portions too much.
In my experiences with it, that was the case.
I don't teach Zone to people at all, unless they are obese and NEED portion control. for athletes it is almost a waste of time.