If you want to do a clean fast, the only things you can consume when you’re fasting are black coffee, unsweetened black/green/white tea, and unsweetened, unflavored water (plus of course any required medications). At first I thought herbal tea was OK, but after reading Gin Stephens’ book Fast Feast Repeat, I learned that it’s not okay if it has any fruit or sweet flavors to it, and even flavored sparkling water is a no-no. Apparently anything that is sweetened, even with artificial sweeteners, or has a sweet taste to it, will trigger your body to produce insulin even if there is no sugar or calories. So no diet soda or gum either.