I actually lost 22 lbs in 2 weeks when I was in the military a few years back. I had to make the weight limit so that I didn't get kicked out. I drank water, ate only oranges, and ran 10 miles a day. When I weighed in, I made the weight and then went to hospital. They put 5 bags of fluid in me and told me that if I ever did this again that I would be written up. I am out of the military now -honorable discharged...not weight related, but I will never forget doing that and will never forget how gaunt I looked. From that experience I learned that losing weight is not really the goal, but losing fat to be healthy is most important...at least for me. I had to make weight at that time, so I was willing to do anything. So stupid.
PS: Oh yeah...it was mostly water, so I gained it all back.