VeryGnawty
"when can I have bread/ potato/ etc.?"
Preferably, never. But if you must eat these concoctions, then eat them whenever you want. I would highly advise simply eating cereal grains or even spaghetti instead of bread. Most commercially available breads are full of all sorts of chemicals. Potato is about useless to begin with, and most ways that people prepare them make it even moreso.
If you must eat bread, find a place that has naturally made breads (as opposed to commercial garbage). If there isn't a place around, then at least buy breads without corn syrup in it. It will probably still have MSG, but at least you'll only be half screwed. I suppose that's better than being completely screwed.