I've done two 40 days fasts in the past - one was on water and the other on juice. I did notice an increase of hair loss while shampooing and after my showers when I'd comb through my hair. This happened in the later stages of the fast. I've read that this is due to metabolic changes that can occur during extended fasts. It does grow back! I have really thick hair anyway so it didn't bother me too much. I know another person (Somer) that did a 60 Master Cleanse/Juice Fast and said she lost handfuls of hair. But hers all grew back also. I'm sure it has a lot to do with your body's chemistry. It was nothing so dramatic that it would sway me from fasting. I'm actually on day 22 of my current fast and no noticable hair loss yet. Good luck with your fast!