It's unrealistic. All of that exercise...what happened to starting out slowly and working up to exercise goals? That is a lot of weight for some of these people to lose in one week. I fear that it would come back on so quickly.
The individuals who plan the show probably keep the contestants from speaking to their families and having outside contact in order to control their emotional and psychological state. But, this probably would have some contestants worrying about what was going on at home.
The show seems to motivate the contestants. A lot of them follow their plan even if they are voted off of the show.