"If I fast and lose some weight will I put on more weight then I lost after I start eating?! "
If you eat the same foods, in the same amounts, doing the same amount of exercising, there's a good chance you will return, or surpass your pre-fast weight.
I have been on numerous extended fasts, and until this last one I always returned to or exceeded my previous weight.
This last time, after gaining about 15 pounds back I have stabilized my weight to only fluxuate about 5 pounds either way. How? I think a lot of it is the fact that I now eat at least 50 to 60% raw. Most in the form of green smoothies. I have been doing enzymes to help in the digestion which wains as you get older.
One things for certain, If you continue as before the fast, you can expect more of the same.