i myself =have been wondering about the stones forming during a fast thing, i need to look into it. but doing a Liver Flush after a fast is the OPTIMAL time to do it. really there is no better time ever. your system is cleansedd and primed to move out toxins and ready to go. if you are thinking of a liver flush, then seize the opportunity a fast gives you and do it. in fact many are saying they have liver flushed with other ingreadients. one said she flushed with just pineapple juice fast. another said he flushed with 9 TB of apple cider vinegar spaced throughout the day. and malic acid is a big one, it helps to break donw stones and get them ready to be flushed so apple juice is good. but ACV has much more malic acid than regular appple juice. you could try adding some bragg's ACV to your apple juice everyday if you like the taste and that will prep you. or you could take some malic acid supplement with your apple juice too.