Biology Defeats Dieting Champions

DANNY CAHILL STOOD, slightly dazed, in a blizzard of confetti as the audience screamed and his family ran on stage. He had won Season 8 of the reality television show “The Biggest Loser,” shedding more weight than anyone ever had on the program — an astonishing 108 kilos in seven months.

When he got on the scale for all to see that evening, December 8, 2009, he weighed just 86.6 kilos, down from 195. Dressed in a T-shirt and knee-length shorts, he was lean, athletic and as handsome as a model.

“I’ve got my life back,” he declared. “I mean, I feel like a million bucks.”

Mr. Cahill left the show’s stage in Hollywood and flew

directly to New York to start a triumphal tour of the talk shows. As he heard from fans all over the world, his elation knew no bounds. But in the years since, more than 45 kilos have crept back onto his 1.8-meter frame. In

fact, most of that season’s 16 contestants have regained much if not all the weight they lost. Some are even heavier now.

Yet their experiences, while a bitter personal disappointment, have been a gift to science. A study of Season 8’s contestants has yielded new discoveries about the physiology of obesity that help explain why so many people struggle unsuccessfully to keep off the weight they lose.

Kevin Hall, a scientist at an American research center, had the idea to follow the “Biggest Loser” contestants for six years after that victorious night. The project was the first to measure what happened to people over as long as six years after they had lost large amounts of weight with intensive dieting and exercise. The results showed just how hard the body fights back against weight loss.

“It is frightening and amazing,” said Dr. Hall, an expert on metabolism at the National Institute of Diabetes and Digestive and Kidney Diseases.

It has to do with resting me- tabolism, which determines how many calories a person burns when at rest. When the show began, the contestants had normal metabolisms for their size. When it ended, their metabolisms had slowed radically and their bodies were not burning enough calories to maintain their thinner sizes.

Researchers knew that just about anyone who deliberately loses weight will have a slower metabolism when the diet ends. So they were not surprised to see that “The Biggest Loser” contestants had slow metabolisms when the show ended. What shocked the researchers was what happened next: As the years went by and the numbers on the scale climbed, the contestants’ metabolisms did not