More Often Than Not, High-Intensity Weight Loss, As Seen On 'The Biggest Loser,' Just Brings The Pounds Right Back

On NBC's long-running series The Biggest Loser, overweight and obese contestants endure rigorous exercise regimens from personal trainers, competing against one another to lose the highest percentage of weight relative to their starting poundage.

In the end, the contestant who has lost the most relative weight is deemed the winner, or "The Biggest Loser," a title that comes with a cash prize of $250,000. The first and second runners-up also go home with a smaller cash prize.

The end of each season is typically euphoric, with each final contestant noticeably slimmer and healthier than at the start of the show, not to mention a newly minted reality television celebrity.

The aftermath of all that, however, can be incredibly disheartening — because with expedited weight loss comes a frustrating boomerang effect.

In a study of contestants from Season 8 of the show (Season 17 wrapped earlier this year), federal researchers found that six years later, most of the 16 contestants weighed just as much as they had when they began the show, if not more. Season 8's winner, Danny Cahill, is known for having lost 239 pounds, the most weight of anyone in the history of the show. On the season finale, Cahill weighed 191 pounds, down from 430. But since then, Cahill has regained more than 100 pounds, putting him at 295 pounds today.

A few years ago, Cahill was at 255 pounds, a weight he maintained by working out for up to three hours a day. When he returned to his job as a land surveyor, he was unable to dedicate as much time to exercise, and his weight climbed again.

There are two major culprits, according to Dr. Kevin Hall, the research scientist who has followed Season 8's contestants since 2009: a slower metabolism and the loss of leptin, a hormone that moderates hunger levels.

Though scientists have known for some time that weight loss slows metabolism, the Biggest Loser study showed that, even when those pounds come back, metabolism doesn't recover. As a result, people like Cahill attempting to keep the weight off must consume significantly fewer calories than other men of their same size, or else the excess turns to fat.

Dina Mercado, another contestant, weighed 173.5 pounds at the finale, down from 248. Today, she weighs 205.9 pounds and burns nearly 500 fewer calories a day than a woman her size. 

"The key point is that you can be on TV, you can lose enormous amounts of weight, you can go on for six years, but you can't get away from a basic biological reality," Dr. Michael Schwartz, an obesity researcher not affiliated with the study, told the New York Times. "As long as you are below your initial weight, your body is going to try to get you back."

Aside from the metabolism issue, weight loss also causes levels of the leptin hormone to fall, making people feel hungrier. At the end of Season 8, contestants had almost no leptin remaining in their bodies. However, even after the weight came back, those levels only reached about half of what they had previously been.

At Pfizer, researchers are looking into a drug that mimics the effects of leptin, so that people who have lost weight can keep it off. The Biggest Loser study, published Monday in the Obesity journal, suggests that pharmaceutical is likely a critical component of maintaining weight loss, given the human body's ability to undo all that hard work.

Only one contestant from Season 8, Erinn Egbert, has managed to keep the weight off in the last six years. At the start of the show, Egbert weighed 263 pounds and got it down to 176 by the finale. Today, she weighs between 152 and 157 pounds, but her metabolism burns 552 fewer calories a day than someone her size.

"It is not clear whether this small imbalance and the resultant weight gain that most of us experience as we age are the consequences of changes in lifestyle, the environment or just the biology of aging," said Dr. Michael Rosenbaum, another obesity researcher.

"The difficulty in keeping weight off reflects biology, not a pathological lack of willpower affecting two-thirds of the U.S.A."