I have trouble explaining sugar addiction to some people. This is a thing of mine that I do not quite understand, but I shut down in discussions because I will all too soon hit a wall anyway and will not know how to argue on. So whilst KNOWING that I have a good point, I will feel like I am "losing" the argument as the other person just has the better arguments. Very frustrating. Can anybody help me? This is how a recent discussion went:

He: Here, have some cake.
I: Nah, thanks, I ´ll pass.
He: Why is that? This is good stuff.
I: I don ´t eat sugar.
(exclamations of surprise on is side, then my explaining that this is not a diet)
He: I think it´s all in your head.
I: That´s the point. And also it´s biochemical.
He: What happens when you eat sugar?
I: It re-enforces my anxiety. And also, I can ´t stop.
He: Is there science to back this up?
I: Experimental science, yes. It´s like with alcoholism.
He: So there ´s no science to back it up?
I: It´s experience values. (I know, I need to get the BE and serotonin stuff right and learn how to represent it.)
He (huffs): It´s a question of willpower.
I: No, it´s not. It´s like with alcoholism.
He: But that´s just it, it´s a question of willpower. I know many friends who just quit drinking from one day to the next. Willpower. They had a drinking problem in college, and then they just quit.
I: Well....
He: So is this like a diet, then?

And so on. At some point the eating disorder question will pop up. But more often than not, I will have just aborted discussion before it gets to this, confining myself to being perceived as weird, neurotical, or both.
Any ideas?