Dr. Weil, Dr. Walt Stoll (askwaltstollmd.com) have both stated that the "stones are nothing but coagulate olive oil.
This has also be corroborated by The Lancet (UK medical journal). They performed an experiement and made these exact stones that people have been passing in a laboratory with components of olive oil and grapefruit.
ALso, the very respected Bastyr University (one of the leading Schools of Naturopathy) states that these cleanses are only releasing the coagulated oil that was ingested from the night before.
Pretty hard evidence coming from some highly respected places. Has me wondering!