A recent study published in Obesity International reports that six years after their dramatic and well publicized weight loss on the TV show “The Biggest Loser,” most contestants had regained the pounds—and on top of that, their metabolic rate had slowed and they were burning fewer calories than before starting the show.

The 14 people studied started at an average weight of 328 pounds burning 2,607 calories a day.  They ended the competition at an average weight of 200 pounds with a resting metabolic rate (RMR) of 2,000 calories a day.  These numbers were not entirely unexpected.  The calories burned (RMR) would be considered “normal” for their overweight sizes at the beginning.  Although the RMR drop was drastic and below the predicted rate for their thinner sizes, researchers have long been aware of “metabolic adaptation” – the slowing of metabolic rate in response to weight loss.

What shocked the researchers is what happened next: as the years went by and the numbers on the scale climbed, the contestants’ metabolisms did not recover.  In fact, their metabolic rates became even slower and the pounds kept piling on.  It was as if their bodies were intensifying their effort to pull the contestants back to their original weight.

Consider the example of Mr. Cahill, one of those most affected.  As he regained more than 100 pounds, his metabolism slowed so much that, just to maintain his current weight of 295 pounds, he now must eat 800 calories a day less than a typical man his size.  Anything more turns to fat.

Senior author Kevin D. Hall of the National Institutes of Health was interviewed by Scientific America: “There used to be a mythology that if you just exercised enough you could keep your metabolism up, but clearly that wasn’t the case,” he said.  “These folks were exercising an enormous amount and their metabolism was slowing by several hundred calories per day.”

Slower metabolisms were not the only reason the contestants regained weight, though.  They constantly battled hunger, cravings, and binges.  The investigators found at least one reason: plummeting levels of leptin, a hormone that controls hunger.  The contestants started out with normal levels of leptin, but by the season’s finale, they had almost no leptin at all.  This would have made them ravenous all the time.  As they gained weight, their leptin levels gradually increased, but only to about half of what they had been at baseline, possibly explaining their urges to eat.

What are the solutions?  In the Fall 2016 meeting of the Obesity Medicine Association, Dr. Deborah Bade Horn DO, MPH, MS advocated that when treating obesity, all physicians measure RMR as a course of treatment to gauge metabolic adaptation.  Dr. Margaret Jackson, a researcher from Pfizer, is currently directing research on a drug that, in animals at least, acts like leptin.  The idea is to trick the brains of people who have lost weight so they do not become ravenous for lack of leptin.

For the contestants like Cahill and the others from Biggest Loser, it surely must be reassuring to begin to understand that the difficulty keeping weight off is more reflective of biology than a pathological lack of willpower.

To view the full study,  Download Energy Expenditure and Weight Control