It was revealed by a former contestant that the producers encourage dehydration. I'm sure a good portion of that 70 lbs. was water.
However, morbidly obese people can lose weight ridiculously fast when normal exercise and healthy diet is introduced into their daily lives.
One of your clients, Rampage Jackson, went from 270 lbs. to 205 lbs. in a month for the Rashad Evans fight using the Dolce Diet, jogging, and training.