Fans of the NBC hit 'The Biggest Loser' may be shocked to know that most of the contestants gain back the weight after the show ends. The drastic changes are not sustainable once the metabolism slows down and is unable to recover.

FOX's Alex Hein explains:

This is Housecall for Health.

For 17 seasons, viewers watched contestants on NBC's 'The Biggest Loser' drastically change their bodies through strict dieting and intense exercise...

However, a new study published in obesity says that the weight loss isn't sustainable because their metabolisms slow down and never recover. Researchers analyzing 14 contestants from season eight found that 13 of them regained some of the weight back and four gained back what they lost, plus more.

At the beginning of the competition, contestants started with an average resting metabolism. As they dieted and exercised to shed pounds quickly their metabolism slowed down. The contestants with the greatest weight lost also experienced the greatest slowing of metabolism.

The show said in a statement that they are considering the study funded by the National Institutes of Health and routinely re-evaluate support systems and comprehensive procedures to ensure contestants receive the best care possible.

For more on this story check FOXNewsHealth.com.

Housecall for Health, I'm Alex Hein, FOX News.