My reason for believing that carbs stimulate the sympathetic nervous system is that I think that, paradoxically, excitement and stress are essentially the same thing. (Excitement initially feels better because thoughts are stimulated and negative emotions are numbed, along with the rest of the body.) Whatever, when it comes to blood sugar, hyper is followed by hypo, so you can get cortisol that way.
I doubt that looking at neurotransmitters is the right way to think about addiction. It is a mental phenomenon which operates on a different level of abstraction. To use an analogy from computing, explaining a software bug does not in general require looking at hardware.
Until we have good explanation of addiction, we can't meaningfully test related theories. So it's hard to take seriously what medical science currently regards as evidence in this matter. However, the fact that AA uses a 'spiritual' programme to break addiction, and that some addicts claim to have been helped by mystical experiences brought on by hallucinogens -- these do seem like significant pointers.
More basically, people commonly report being in two minds about food, which is the hallmark of addiction.