Can you really regain 10kg of pretty much just water that quickly? Wow, didn't know that.
Depends on the fighter, incredible how they do it though, you'd think it would take a lot out of them. Read this, it's pretty interesting about GSP

http://sports.yahoo.com/mma/blog/ca...nd-GSP-8217-s-weight-cutting-a?urn=mma-wp1628