I have heard people say this in regards to CE's over and over and I am not sure where this information is coming from. I suspect people may assume this is happening because some people can feel very weak afterwards. This has more to do with toxins being stirred up and not being completely expelled with the enema.
I have asked a few practitioners who recommend these both affiliated with Nutritional Balancing, the Kelly and Gerson therapies and the answer is....NO. coffee enemas do not deplete minerals. No one had explained to me why this is, but here is my take on this: Coffee or any other enema of similar volume do not deplete minerals because the liquid is held in the lower part of the colon only and so whatever is expelled, it's from this part of the colon.....our minerals have already been absorbed by the body at this point.
Now, if you have diarrhea, its a different story because its an evacuation of most if not all the contents in the entire small and large intestine whereas assimilation of nutrients had not been completed. Now saunas, those are different .... Hope this helps.