Switching up your diet can help you shed pounds. But to keep that lost bulge at bay, ambitious dieters may have to turn to exercise—a lot of exercise—according to a study on 14 former contestants of The Biggest Loser.

On average, the contestants who kept their weight down six years after the television contest did so by taking on more than triple the amount of physical activity recommended by the Centers for Disease Control and Prevention. That is, they burned around 12 kilocalories per kilogram of their weight per day. That works out to a daily total of more than 80 minutes of moderate exercise, such as brisk walking, or 35 minutes of vigorous exercise, such as jogging—and weekly totals of 560 minutes of moderate exercise or 245 minutes of vigorous exercise.

Currently, the CDC recommends that adults get 150 minutes of moderate exercise or 75 minutes of vigorous exercise per week.

The findings, published Tuesday in the journal Obesity, should be interpreted cautiously. It was a study on just 14 people, and they undertook a unique and extreme diet-and-exercise intervention on a reality show. Still, the authors point out that the data echos results from other larger studies showing that exercise is key to weight maintenance. It also falls in line with earlier work on Biggest Loser contestants showing that their metabolisms became sluggish after they dramatically dropped pounds on the show.

Last year, the same authors found that the contestants’ resting metabolic rates declined during the show and were still low six years later. Based on their individual weights, they were burning a mean of about 500 fewer kilocalories each day than would be expected for people their sizes. Such a decline in metabolic rate helps explain why super-sized exercise is required to keep the weight off.

“Long-term weight loss requires vigilant combat against persistent metabolic adaptation that acts to proportionally counter ongoing efforts to reduce body weight,” the authors, led by Kevin Hall of the National Institutes of Health, concluded at the time.

Feeling the burn

For the new study, Hall and colleagues assessed contestants’ energy expenditure, body fat, and weight outcomes at four time points: just prior to the contest, six weeks later, 30 weeks later, and six years later.

They calculated how much energy the participants were burning using the doubly labeled water method. For this, contestants drank water with two isotopes: 2H 2 18O. This labeled water equilibrates with the body’s total water, and the two isotopes are released differentially. The hydrogen is peed out and the oxygen can leave in pee or in breath as carbon dioxide. With measurements of the isotopes in spot urine tests, researchers can calculate how much carbon dioxide a person is creating, which indicates their metabolic rate. From there, the researchers can calculate how many kilocalories they’re burning each day. And, by subtracting resting-state metabolic measurements, they can also estimate how many kilocalories they burned from physical activity.

Next, the researchers split the 14 contestants into two groups: the “maintainers” and “regainers.” At the start, the contestants’ average weight was 150 kg (329 lbs), which dropped to 92 kg (202 lbs) at the 30-week point. But six years later, it had bounced back to about 132 kg (290 lbs), with a lot of variation and a median weight loss of just 13 percent. For the maintainers group, the researchers selected the seven contestants above that median. On average, they weighed 25 percent less than they did when they started the contest. The remaining seven were the regainers, who on average were one percent heavier than they were at the start of the contest.

Hefty data

There was a stark difference in physical activity levels between the two groups. The regainers’ average physical activity level at the six-year point was about 34 percent higher than it was at the start. But the activity level of the maintainers leapt a whopping 160 percent higher.

Overall, the researchers found that those who stepped up their exercise the most between the contest’s start and the six-year point tended to regain the least weight after the contest. But boosts in exercise didn’t seem to have any clear correlation with weight loss at the six-week and 30-week time points.

On the other hand, calorie intake—diet—helped take off pounds but didn’t seem to keep them off. Calorie cutting was linked to weight loss overall during the six years—and directly linked to weight loss at the six-week and 30-week time points. But, when the researchers looked at the change in calorie intake from the start to the six-year point, there was no correlation with the amount of weight regained in the period after the contest. That is, some who cut the fewest calories by the end still maintained their weight loss, while others who cut lots of calories still regained dozens of pounds.

Together, the findings suggest that calorie cutting was critical for initial weight loss, but exercise was what kept the weight off in the six-year follow-up. Several other studies have come to the same conclusion. For instance, a 2014 study of weight loss maintenance in more than 5,000 adults over eight years found the most successful participants were significantly more physically active than those who regained more weight.

Hall and colleagues conclude:

Our results support previous recommendations that large and persistent increases in [physical activity] may be required for the long-term maintenance of lost weight.

Obesity, 2017. DOI: 10.1002/oby.21986 (About DOIs).