You know, what I've found is that if someone gives me grief about not wanting bread, rice, etc, I just tell them I have a food allergy (generally a wheat allergy or rice allergy). It is amazing how they will shut up if they think you are allergic to the food rather than simply choosing not to eat it and they will suddenly be very accomadating. This is particularly so if it is someone working in a resturaunt.

And hey, it isn't that much of a lie. Those heavy carb substances are at least as detrimental to my system as a food allergy!