The research revealed a kind of metabolic adaptation occurred as the subjects rapidly lost weight. Measuring the resting metabolic rate (RMR) it was discovered that by the end of the competition the rapid weight loss has also slowed down each individual's metabolism.
A follow up study in 2016 looked at the same subjects six years later and discovered these metabolic changes had persisted. Despite the subjects regaining varying amounts of weight in the years that followed the competition, the slowing in RMR initially detected years ago had remained.
This was an unexpected result. It was hypothesized that RMR could more dynamically reflect weight fluctuations, so as individuals regained weight over the years their metabolism would reflect those changes. But this wasn't the case, and six years later those Biggest Loser contestants displayed the same average RMR as they did at the end of the competition, despite any weight regain.