South Beach Diet - stupid question maybe

ok i am stressing now since i have been eating fat free cheese all week. i used it on my casserole just now and looked at ingredients.

yeast
potato starch

are these 2 allowed? i'm not really up on baking, so am not sure even what yeast is except it makes bread rise ( i think) :?:
and well potato starch must be derived from potatoes?!?! am i overreacting? fat free chesse is allowed

Don't stress out over it. Just look for LF or FF without the potato starch next time.
By the way, the only stupid question is the one that is unasked!

I dont think potato startch is allowed, but at least you know now rather than later!