I have read more detailed explanations why hairloss happens to some when fasting and I wish I had some links to point you to them. I have never done an MC shorter than 21 days including the 1st I did which was a 40 dayer. I originally only planned for 2 weeks but I was feeling so energized that I continued to 40 days. To date I've done at least a dozen 40 dayers over a 9 +/- year period. I've switched over from straight MC for 40 days to where I switch to veg juices at around 21 days or so. I have found this very beneficial as the system continues cleansing but one is also infusing the system with megadoses of vitamins minerals and live enzymes. There is a post further down this page where I describe "The Switch"