It is a question that plagues all who struggle with weight: Why do some of us manage to keep off lost pounds, while others regain them?
Now, a study of 14 participants from the “Biggest Loser” television show provides an answer: physical activity — and much more of it than public health guidelines suggest.
On average, those who managed to maintain a significant weight loss had 80 minutes a day of moderate activity, like walking, or 35 minutes a day of vigorous exercise, like running.
The researchers conducting the new study did not distinguish between purposeful exercise, like going to the gym and working out, and exercise done over the course of the day, like walking to work or taking the stairs.
Guidelines from the Centers for Disease Control and Prevention, by comparison, call for at least 150 minutes a week of moderate exercise, or 75 minutes a week of vigorous exercise for healthy adults.
Although the study is very small and must be replicated, Dr. Hall said, it is the first to assess obese people years after they lost weight with state-of-the-art methods to measure the calories they had consumed and the amount of exercise they had done.
The researchers did their measurements when the contestants were chosen, and again at six weeks, 30 weeks and six years after the contest began.
After ‘The Biggest Loser,’ Their Bodies Fought to Regain Weight
Contestants lost hundreds of pounds, but gained them back. A study of their struggles helps explain why so many people fail to keep off the weight they lose.
“The findings here are important,” said Rena Wing, a psychiatry professor at Brown University and a founder of the National Weight Control Registry, which includes more than 10,000 people.
The food eaten “is the key determinant of initial weight loss. And physical activity is the key to maintenance,” she said.
The study also helps explain why that might be. One consequence of weight loss among the Biggest Loser participants was a greatly slowed metabolism.
The subjects were burning an average of 500 fewer calories a day than would be expected, Dr. Hall and his colleagues found. In essence, their bodies were fighting against weight loss.
Those who kept the weight off “are countering the drop in metabolism with physical activity,” Dr. Hall said.
During the initial weight loss, the equation was different. Then, the difference between how much weight “Biggest Loser” contestants lost could be explained by the number of calories they cut from their diets. The amount of exercise did not distinguish those who lost more from those who lost less.
The contestants competed for six months to see who could lose the most weight. Participants followed a grueling diet and an exhausting exercise program.
Contestants’ average weight at the start of the show was 329 pounds. At the end, it was 200 pounds, a 129-pound loss. But six years after the study ended, their average weight rebounded to 290 pounds, just 38 pounds less than when they started.
That average, though, hid wide variations.
To learn more, Dr. Hall and his colleagues divided the group of 14 into two. There were the “regainers,” the seven participants who ended up after six years weighing five pounds more on average than they had at the start.
CreditLuke Sharrett for The New York Times
And there were the “maintainers,” the seven who maintained an average weight loss of 81 pounds.
To measure the number of calories the contestants burned, the researchers asked the subjects to drink “doubly labeled water,” in which hydrogen and oxygen atoms are at least partially replaced by stable isotopes, which have a different atomic mass.
The oxygen isotopes appear in carbon dioxide exhaled by subjects, which allowed the researchers to estimate the average amount exhaled each day. The more calories burned, the more carbon dioxide exhaled.
Dr. Kerns, a contestant in Season 3 of the show, says she has managed to keep off 100 pounds only by tracking everything she eats and by exercising on an elliptical cross-trainer for 35 to 40 minutes a day. In addition, her job requires her to walk around the hospital seeing patients.
She has learned that she cannot relax this regimen if she wants to maintain her weight. “My natural tendency is to regain,” she said.
Erinn Egbert was a candidate for Season 8 of the “Biggest Loser” but ultimately did not make the cut. So she went home “to figure it out on my own.”
She hired two trainers and followed a diet and exercise program while she finished her senior year at Ohio State University. She weighed 237 pounds when the show began and lost about 120 pounds.
She has maintained a weight that is just eight pounds more. She does it with rigid portion control and regular, intense exercise — 45 minutes to an hour a day, Monday through Saturday, doing the Beachbody programs, a challenging combination of strength training and cardiovascular exercise.
Ms. Egbert, who is 30 and lives in Lexington, Ky., says she learned the importance of working consistently to stay thin, even with a slowed metabolism.
CreditIlana Panich-Linsman for The New York Times
“You have got to keep at it every single day,” she said.
It’s a difficult task for virtually anyone, Dr. Kerns said: “The amount of time and dedication it takes to manage one’s food intake and prioritize exercise every day can be an untenable burden for many people.”
“It’s totally unfair to judge those who can’t do it,” she added.
Dr. Hall agreed. “The idea that people who regain lost weight are necessarily slothful and gluttonous is an unfortunate stigmatization that is not based in fact,” he said.
Danny Cahill, who is 47 and lives in Tulsa, Okla., is among those who found it increasingly difficult to keep up the sort of regimen he needed to avoid gaining weight.
He won the “Biggest Loser” competition in Season 8. He weighed 430 pounds when the show began, and lost 239 of them.
For the four years after the show, he exercised more than two and half hours a day and gained back just 40 pounds.
Then the injuries began, forcing him to cut back his workouts to one and half hours a day. His weight crept up to 235 pounds.
The next year, “my body just started breaking down,” he said. “I had a foot injury, a wrist injury. I couldn’t keep it up.” And he was exhausted.
His weight went up to 300 pounds. For the last two years, his weight has remained stable at about 340 to 350 pounds, “but only because I am eating as very little as I can,” he said.
“That’s the disheartening part,” Mr. Cahill said. Losing the pounds is one thing. Keeping them off?
“I am still struggling with it,” he said.