Re: Possible 40 day water fast for a slimmer stature? Tips and advice would be very much appreciated...

You're likely to lose on average 10% of your body weight in the first few days. That will mostly be water, and no worries, when refeeding that will come back just fine. Then every fasting day you'd likely lose 1/2-3/4 lb. 21 days may be as much as 14lb.
At the end of a 21 day fast - you could be as much as 27 lb less. So 103lb worst case.

I don't think that is very healthy longer term, but if you got there before you re-feed and put weight back on in a good way with better gut flora - maybe that could be OK.
Someone who knows more should come along - I hope.
Thanks.
Srinath.