Quoting Mum to a Monster:" That will probably last for the time you are on it and that is it. The next day it will be right back ... [snip!] ... they got back to base they were moving back to their normal weights because they were back to eating their usual junk food."
I'm almost 100% sure that they didn't gain it back because of what they ate when they came home. If you eat 3 MREs, that's almost 4000 calories (roughly). They probably just lost a ridiculous amount of weight because of the strenuous things they were doing.
I would do a diet like this if I wanted to lose a couple of extra pounds for a wedding or a beach day. I wouldn't count on the weight to stay away.