Caffeine is bad because it makes you dehydrated. I love my hot tea but my doctor discussed this in detail because I didn't want to give it up before surgery. Also a lot of herbal teas affect your body. So no herbal tea until after surgery. If your too dehydrated then you can get dizzy and pass out while your loosing weight quickly. The decaf variety of coffee still has some caffeine in it. Also many coffees have added calories from milk and sugar and flavors added to it. Decaf black tea still has small amounts of caffeine but it's small enough my doctor said it was ok. I was still dehydrated before surgery even though I completely gave up teas. They had a hard time getting a vein. I almost had to postpone surgery.