I'm a bit of a purist when it comes to fasting and I'm afraid I'm a bit rusty. It's been a few years since my last fast...

I think it is believed that the ingestion of protein will take your body out of the stage of autolysis, which is what your body needs in order to repair and detox. I've never used protein of any sort (fasted many times, as long as 145 days and 105 days, 40, 20, etc) but I've had several different herbal teas like peppermint and chammomile, just none that would cause a release of water since you don't retain much water while fasting.

I don't know of anyone who's had coffee while fasting, unless it was in an enema bag.