Why The Biggest Loser Contestants Gain Back the Weight

It’s an unfortunate truth that many people who lose a significant amount of weight will gain it back. But a new study of contestants of the popular reality show The Biggest Loser suggests that a slowed metabolism—not a lack of willpower—is largely to blame.

In new research to be published in the journal Obesity, researchers followed contestants from The Biggest Loser season 8 for six years to see what happened to them after they lost so much weight, the New York Times reports. Led by Kevin Hall, a scientist at the National Institute of Diabetes and Digestive and Kidney Diseases, the researchers found that people’s resting metabolism—how many calories they burn when they’re at rest—changes dramatically after weight loss.

The men and women had normal metabolisms for their weight when they were obese, the Times reports. However, once they dropped a massive amount of weight, their resting metabolisms slowed so significantly that they were not burning enough calories to maintain their new size. This is a normal reaction to weight loss; what was surprising was that as time passed and the people gained back weight, their metabolisms continued to slow, making the process harder.

The winner of season 8, Danny Cahill, lost nearly 240 pounds in less than a year. Since then, he’s gained back 100 pounds, the Times reports. But the findings may also apply to people who lose less.

The new study adds to a growing body of research aimed at understanding why it’s so difficult for people to lose weight, and why some are more successful than others. Other recent studies have suggested that people’s bodies respond dramatically differently to the same foods. In the future, weight loss advice may need to be more personalized, some experts suggest.