While there is no clear definition of what constitutes "unsafe" weight loss, it's probably fair to say that "The Biggest Loser" flirts with that blurry line at the best of times. Add some additional measures to the already-extreme methods imparted on TBL contestants and you have a recipe for a potentially dangerous situation.
At least a couple of Biggest Loser contestants have admitted to intentionally dehydrating themselves to accelerate their progress.
Therein lies the most fundamental problem with TBL - using scale weight as the sole determinant of success and hence victory. This obviously leaves things open to all sorts of behind-the-scenes tactics to shed more weight. Moreover these are just a couple of examples, but who knows what kind of pills, laxatives or other adjunct measures contestants are trying.
In the world of reality TV, drama matters - the more extreme the weight loss, the greater the drama, the greater the ratings. Also, severe caloric restriction + intense exercise very make people grumpy - there's your built-in drama right there.
When it comes to contestants, $250K is a good chunk of change. Add to that, the possibility of endorsements, book deals, magazine covers and suddenly the stakes are pretty high.
To quote this article
Drama is one thing when you're vying for the attention of a washed up hip hop star, airing your dirty laundry, eating bugs, or repelling down skyscrapers, but it is entirely different ethically when health risks are involved."
Nobody wants to see a show where people lose 2 pounds a week on a sensible exercise and nutritional program.
It isn't uncommon for contestants to lose 15lbs in a single week. And we have to remember that TBL contestants are pre-screened and medically monitored throughout their extreme regimen.
For the average Joe/Jane, the Biggest Loser ups the ante of weight loss expectation. We may not have a ton of money to gain from being thinner but fitting into a wedding dress, going to a sunny destination and other occasions that call for fast weight loss can spark some risky behaviour.
Exercising in heat or other dehydrating methods can cause heart problems and potentially fatal electrolyte imbalances. Gallstones, nutritional imbalances, irritability and constipation are also common in very rapid weight loss over the course of several weeks.
At the very least, extreme weight loss methods don't last.