Concerned about losing too much weight.

Hi. I'm on day 12 and until apart from an occasional hunger pang everything
seems to be going well. The only thing i'm concerned about is losing too much weight
which could cause problems.

Even before the cleanse i had a relatively thin build (64Kgs or so for 1.75 meters)
I don't know how much kg's i've lost during the cleanse (i weight measuring device :) ) but people keep remarking that i'm getting thinner and thinner.

I was wondering if there's anyway to determine by means of calculation how much weight lose is too much because i don't want to get into some complicated situation because i pushed too hard (although in terms of physical energy i'm more or less in the same level as before i started or even better).

Your help is very appreciated.