PhotoThe NBC reality series “The Biggest Loser” has been an inspiration to many obese people. They have watched as contestants embraced a supervised, on-camera lifestyle transition to a healthy diet and exercise.

Even the contestants who didn't win went home happy, with slimmer, lighter bodies. But a team of U.S. researchers wondered what happened next? Did the feel-good story continue, off-camera? In most cases, it did not.

The researchers investigated 16 of the show's contestants, 14 of whom participated in the follow-up study. All but one gained back some of the weight. Four regained everything they lost, and then some.

The study found the 14 participants lost an average of about 128 pounds, regaining about 90 pounds over six years.

Looking for 'why?'

But that wasn't the point of the study – the researchers suspected they might find some regained weight, since that often happens to dieters. The real question they wanted to answer was “why.”

The “why” appears to center on changes to metabolism, which is kind of like your body's miles-per-gallon (MPG) rating. You want your body to have the MPG of a Hummer, not a Prius.

In their study, the researchers determined that the dramatic weight loss altered the body's metabolism, the rate at which it burns calories. As subjects dropped pounds, the body slowed the rate at which it burned calories. They call it metabolic adaptation.

Using before and after data for the contestants, the researchers found their resting metabolic rate (RMR) slowed in the years following the show.

The researchers said their study, supported by the National Institutes of Health (NIH), is probably the longest follow-up investigation of the changes in metabolic adaptation and body composition following weight loss and regain.

Suppressed RMR

Photo“We found that despite substantial weight regain in the six years following participation in 'The Biggest Loser,' RMR remained suppressed at the same average level as at the end of the weight loss competition,” the authors wrote.

They found mean RMR after six years was about 500 calories a day lower than expected, based on the measured body composition changes and the increased age of the subjects. The contestants who lost the most weight, they said, also experienced the greatest slowdown in RMR at that time.

Those most successful in keeping the lost weight off after six years also experienced greater ongoing metabolic slowing.

“Metabolic adaptation persists over time and is likely a proportional, but incomplete, response to contemporaneous efforts to reduce body weight,” the study concludes.

The takeaway

The takeaway, however, is not that obese people should not try to lose weight and adopt a healthier lifestyle, far from it. Rather, it's an acknowledgment of the physical obstacles your body can throw up to maintaining the weight loss.

Despite their weight regain, the contestants were “quite successful” at long-term weight loss compared with other lifestyle interventions, the study found. The researchers also found that those who experienced the biggest metabolic change did not experience the greatest weight regain and those who were most successful in keeping the weight off had pretty much the same metabolic slowdown.

So the lesson, the researchers say, is “long-term weight loss requires vigilant combat against persistent metabolic adaptation that acts to proportionally counter ongoing efforts to reduce body weight.”

It should be noted that participants in “The Biggest Loser” all had close medical monitoring during the show. You should not undertake any sort of significant weight loss effort without consulting a doctor first.  

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