Regardless of the truth or not about how certain foods affect different people, I am sick of hearing it. When I was religiously following a low-fat diet, ten percent fat, I NEVER mentioned it. Why should I? I saw no reason to compare my food choices to what anyone else was eating. Similarly, I do not make a point of my being a vegetarian unless it is for some reason critical - in a steak house I might have to mention it to the waiter quietly as a way to get suggestions (although even there I can usually manage quite well without bringing it up).
Why can't we just eat? Why do we have to discuss everything we eat and can't eat and compare what we eat with what someone else eats? What the hell?? And I can't help feeling insulted when people shove their bread at me. What I hear, the undercurrent: "I'm careful about what I eat so I'm giving this to you." It's a bit like the dieters who bake incredible desserts and then offer them to others, never taking a bite themselves. There is something aggressive about it. To me.
The sad thing is that this aspect of these friends makes me think twice about doing things with them. And that's a shame because in other ways they are really fun to be with.