We studied sixteen contestants from season 8 of the The Biggest Loser and measured changes in total energy expenditure, resting metabolic rate, and body composition over the course of a 7 month competition. The study participants lost almost 40% of their starting body weight bringing them from morbid obesity to just at upper edge of the overweight category according to BMI. We found that participants were able to preserve their lean tissue mass through vigorous exercise, despite massive overall weight loss. The participants also experienced substantial improvements in their metabolic health. The study found that the contestants metabolism slowed quickly and disproportionately to their weight loss and this adaptation impeded the rate of weight loss and may predispose this group to regaining weight following the competition.

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Knuth, Nicolas D; Johannsen, Darcy L; Tamboli, Robyn A et al. (2014) Metabolic adaptation following massive weight loss is related to the degree of energy imbalance and changes in circulating leptin. Obesity (Silver Spring) 22:2563-9
Hall, Kevin D (2013) Diet versus exercise in "the biggest loser" weight loss competition. Obesity (Silver Spring) 21:957-9