Contestants lost hundreds of pounds during Season 8, but gained them back. A study of their struggles helps explain why so many people fail to keep off the weight they lose.
Two individuals, each of the same size/weight, but one who had lost a substantial amount of weight to arrive there, end up with significantly different resting metabolisms, such that it becomes impractical to maintain the weight loss. The alternative for those people is to devote substantial amounts of time to exercise to maintain caloric burn rates that counter their abnormally low metabolisms. That’s part of the lifestyle change – crash/fad diets do not work for the long term.