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NATIONAL HARBOR, Maryland -- In order to keep off weight after participating in "The Biggest Loser" reality-TV show, contestants had to keep up high levels of physical activity, researchers reported here.

Six years after appearing on the competition show, contestants who maintained weight loss increased their physical activity by 160% ± 23% from pre-show levels, whereas those who regained weight increased activity by only 34% ± 25% (P=0.0033), according to Jennifer C. Kerns, MD, MSHS, of the Washington, D.C., Veterans Affairs Medical Center, and colleagues.

At this time, maintainers of weight loss reported an average physical activity expenditure of 12.2 ± 1.3 kcal/kg/day versus 8.0 ± 1.4 kcal/kg/day for regainers (P=0.04).

There were no significant differences reported for energy intake between weight loss maintainers and weight regainers (-8.7% ± 5.6% versus -7.4% ± 2.7%; P=0.83).

Findings were presented at the annual ObesityWeek meeting, as well as online in the journal .

"['The Biggest Loser'] is a reality TV show in which people with class III obesity competed with each other to lose the most weight over about 30 weeks through an intensive lifestyle intervention -- diet and exercise," explained Kerns. She had appeared on the show herself in the 2006 season, losing 108 lb in 8 months.

The study included 14 participants in a subsequent season of the show, with an average baseline BMI of 49. The researchers collected data at baseline -- prior to the competition -- as well as at week 6 and week 30 of the competition, and again 6 years after the conclusion.

Body composition was measured using dual-energy x-ray absorptiometry after an overnight fast. Resting energy expenditure was assessed with indirect calorimetry after a 12-hour overnight fast. Physical activity levels and energy intake were both assessed using doubly labeled water, which measured the average rate of carbon dioxide production.

While appearing on the show, the participants lost an average of 127 lbs. At the 6-year follow-up, median weight loss for the cohort was 13%, with maintainers weighing an average of 24.9% ± 3.8% lower than baseline whereas regainers ended up a mean 1.1% ± 4.0% above baseline (P=0.0005).

From baseline to the 6-year follow-up, percentage of weight change was tied to percent change in physical activity (r=-0.63, P=0.017), but not percent change in energy intake (r=0.27, P=0.36).

Similarly, absolute weight change was not linked to percent change in energy intake (r=0.46, P=0.10). However, it was significantly associated with both physical activity (r=-0.57, P=0.035) as absolute energy intake changes from baseline (r=0.54, P=0.046).

Most of the weight regained 6 years after the competition was regained as body fat, the researchers noted, adding that fat mass was strongly tied to physical activity changes (r=-0.82, P=0.0003).

"This is really just consistent with all of the other research that we have so far that has generally shown that the diet component may add more to a weight loss program than exercise does, whereas exercise maybe becomes more important in the weight loss maintenance phase long term," said Kerns.

She noted limitations including the very small sample that is "a really unique population," who began with obesity and then experienced a very dramatic weight loss, which may hinder the generalizability of the findings.

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