Its a no fat flush protocol which promotes the formation of stones, and then so many of us have taken prescription drugs, which many of, if you read the PDR, affect the liver negatively and over the years things like parasites have congregated in our liver/gallbladder. Its one of the major filters of the body and stuff the body perceives as a toxin will often get encapsulated and thus the formation of stones. Things like lecithan and a diet high in good fats will help keep down the formation of stones, but on the Master Cleanse, the formation is promoted. That is also why it is recommended to flush the liver/gallbladder before the Cleanse as well as after....