Let us hope that Telman reads this he often has the answer.
I have to assume that it has to do with the stopping of bile production. The same warning is with fasting in general.
Also after you do a master cleanse it is suggested to eat for a few days to get the bile flowing again, since you need it to push out the stones.
According to Ayurveda medicine my bodytype is pitta and for me the Master-Cleanse is not good.
I read it in following message. Since the person with the original question was feeling ok I have to assume she is a different bodytype, but the bile problem still applies to her. //www.curezone.org/forums/m.asp?f=337&i=2651
Here is a message from someone who did very well with Master-Cleanse and LF, we all react differently. Also read the answer to it. //www.curezone.org/forums/m.asp?f=337&i=7558