When you add Psyllium and or usually Bentonite as in traditional PB shakes you are no longer doing the Master Cleanse and you have essentially turned the MC into a colon cleanse and you will not be reaping the full reward of how the MC was designed to work. Further because of the highly absortive nature of the Psyllium and the posibility of the Bentonite becoming plaster like in an empty system you are not only absorbing what little nutrition is provided and cleansing components of the MC but also run the risk of really pluging the system even worse.We had a poster a coupla of years back that wound in the hospital plugged up from doing the PB shakes during the MC.
The main mode of how the MC works is by giving the digestive system a rest so the energy otherwise used for digestion is used to cleanse and heal. While the psyllium is mainly inert fiber there is also soluble fiber that will activate digestion and the digestive's system peristaltic action will also be activated to push all that fiber out
People spend a lifetime putting crap in their system and the FACT is you are not going to get it out in one fell swoop. The MC works in a very simple elegant way as designed. More or adding/combining with other cleanses is NOT better. Each cleanse works great on their own when done separately and allowed to function as designed. If it ain't broke DON'T FIX IT. Read the link below from the FAQs for more insight on adding the PB shakes to the MC