I believe everyone has different levels of toxins in their bodies (depending on their exposure and DNA).
Some bodies cushion the harm the toxins can do by adding fat; others try to release the toxins through the skin (breakouts, sores, etc) & digestive system (constipation can result).
The Master-Cleanse will give your digestive system a break to concentrate on building up your immune system.
I went 58 days. You can read about my journey by clicking on SHOW ALL MESSAGES POSTED BY LiveBetterServeJesus above.
My body didn't fully cleanout until about Day 40 (No More B.O.).
I think the reason the fast is at least 10 days is to clear out your system and help break alot of the cravings for bad food you might have had before.
This is a great website...lots of info.
Use the search box, read the Recommended Posts in this and ARCHIVE FORUMS... there is so much here.