Answer: This is a great example of the difference between reality and television. The contestants on the show get to exist in a controlled environment where their primary daily activity IS activity, and they are medically supervised during their time on the show. It is not uncommon for contestants to do 4-8 hours a day of intense exercise. Add to this a low- or very-low calorie diet and you have the recipe for weight loss: increased calories out and decreased calories in. Also, especially prior to weigh-ins, dehydration strategies are not uncommon, leading to additional weight loss. So, a huge energy expenditure coupled with a sparse calorie intake yields a dramatic calorie deficit and the loss of fat, muscle and water, yielding impressive numbers on the scale. And no, it’s not safe for most overweight people.
In the real world, rapid weight loss can lead to weight regain. In fact, there has been a lot of controversy around former contestants regaining much of the lost weight. Generally a 1- 2 lb loss per week (more if you have a lot of weight to lose) creates a realistic lifestyle that, for most people, is more sustainable. If you cannot maintain the severity of the lifestyle necessary to promote rapid weight loss, then you most likely will not maintain the weight loss. For more info, read Keys to Permanent Weight Loss, and Proven Strategies for Weight Loss.