This is incorrect. Bentonite Clay is not "digested" by the body, and the minerals in the clay - if the body has chosen to pick them up - will not redirect significant amounts of energy to be used for their metabolism. You can use Bentonite clay during a fast, if it is one of the cleaner grades. If it is not a very clean clay, you will risk momentarily halting the fast with its use (because of possible digestion). However, most internal-use "bentonite" sold is of a cleaner variety. Drink more water if you consume Bentonite clay during a fast. (Sorry for the way way late reply, but I didn't like to see such a wrong answer!)