Winners of The Biggest Loser, the NBC reality show in which contestants compete to lose massive amounts of weight, tend to pack the pounds back on after the cameras turn off, a new study in the journal Obesity reports. It’s a disappointing outcome for anyone who’s looked to the series for inspiration, but it shouldn’t be that surprising, either. The whole idea that an extreme weight loss regimen can turn you from fat to fit — and keep you that way in the long run — was never proven, scientifically speaking, to begin with. The show’s 17 (and running) seasons have pretty much been a long, unchecked experiment on obesity.

While strict dieting and intense exercise will obviously cause people to lose weight rapidly, no one seemed to bother much with how to keep the weight off once contestants went back to their regular lives. And, to be fair, there haven’t been many opportunities for researchers to study this; it’s unlikely that any ethics board would approve a diet plan as extreme as the one on the show. But the show’s existence presented the opportunity for scientists from the U.S. National Institutes of Health, who carried out the study to try to figure out whether keeping lost weight off was possible at all.

To carry out their study, the researchers checked in with The Biggest Loser contestants from Season 8 at the end of the competition in 2009 and again in 2015, comparing their body weight, fat content, and resting metabolism rate at the beginning and end of that six-year period. By the end of the show, the 14 contestants involved in the study had lost, on average, 128 pounds each. But after six years, all but one of them had regained a significant amount of weight.

It wasn’t because contestants had lapsed into old habits. Analyzing the data on metabolic rates before and after the six-year period, the researchers uncovered a surprising and difficult-to-swallow truth: The body is actually incredibly resistant to weight loss.

Scientists have long known that our metabolisms — that is, how quickly we burn calories when we’re at rest — slow down when we make an effort to deliberately lose weight. This explained why the contestants in the study had slower metabolisms at the end of the show than they did at the beginning. What the scientists hadn’t been able to confirm until now was that metabolic rates would stay slow for years after the weight loss occurred, stubbornly pushing the body back towards an obese set point.

After six years, the contestants were burning 500 fewer calories a day than they would be expected to, given their weight, which is why it became increasingly hard for them to keep it off. Losing weight rapidly, it seems, is the exact opposite of what the body is engineered to do, and it could have dangerous health implications in the long term. We’re just realizing it about 17 seasons too late.

The study comes as bad news for the contestants that served as guinea pigs in an epic televised weight loss experiment, and it calls into question how ethical it was to launch the show in the first place. Whether the results of the study will have any impact on the future of the show remains to be seen, but it’s likely that it won’t. After all, it’s the experimental nature of reality shows that make them so compelling to watch.