This can be a very controversial subject...
First off I would divide things into 2 groups...Those with healthy pouches and those with sick ones (crohns, pouchitis, IPS...), those would be pouches with much more sensitivity and therefore may be more suseptible to irritants like coffee etc...but healthy pouches that have no underlying sensitivities could do just great on bad diets...
I lived for years on a very restricted diet due to finances...essentially rice, yoghurt and coffee & coke. I drank at least 20 coffees/day on an empty stomach without incident. My pouch was just fine (my waistline, not so much)...
I know pouchers, k and j who can eat anything, drink anything and come out smiling...other can't but I am not sure that there is a general rule that is written in stone.
It is maybe preferable to eat healthy (duh!) but not dangerous for your pouch if you don't...you might want to creat a poll to see what people think, it would give you better percentages.
Ps, how are you doing?
Sharon