Even though I was a contestant on The Biggest Loser during season 3, I didn’t actually get to live on the ranch and compete like the contestants do on most seasons, since there were 50 of us and only 14 stayed on the ranch. I was one of the “36ers” who lost the weight on our own at home. So how people managed to lose 30 pounds or more in one week, I had no idea… until I was the doctor for the show on seasons 4 and 5, that is.
First, it turns out that a “week” on TV is sometimes filmed over 7 days, but sometimes the filming schedule is longer and it might be up to 14 days before the next episode is filmed. They all say “this week” and make it seems as if every episode occurs 7 days after the last, but that’s just not the case. So, those 30 pounds might have been lost over 2 weeks, not just one.
Second, the contestants pretty much universally dehydrate themselves before weigh-ins. They cut out carbs (which makes them deplete their glycogen stores, which also makes them lose water with it) and cut out salt to lose as much water weight as they can through diet, and then they exercise and sweat without drinking water to replace their losses. This drops an enormous amount of weight due to water losses without actually requiring any fat to be lost.
Finally, they actually do lose a lot of fat. They might work out up to 8 hours in a day, and are watching their caloric intake closely. So a good amount of the weight lost is real fat loss. Just don’t be discouraged if you can’t lose the same amount of weight at home, since you don’t have 8 hours a day to dedicate to exercise and you’re not taking extraordinary measures to drop water weight.