After ‘The Biggest Loser,’ Their Bodies Fought to Regain Weight

Actually, it's after ANY large amount of weight lost due to calorie restricted diets, even WFPB no S-O-S ones. Some of the Star McDougallers frequently mention how they have to eat less and less starch, less calories, first to lose those last few pounds, then to maintain their lower weight. Some Stars lost over 100 pounds, regained, and lost them again. 

Doctors, especially obesity experts, have known about this happening for DECADES, which is why they now push for weight loss surgery and weight loss meds. 

After ‘The Biggest Loser,’ Their BodiesFought to Regain Weight
Contestants lost hundreds of pounds during Season 8, but
gained them back. A study of their struggles helps explain
why so many people fail to keep off the weight they lose.
By GINA KOLATAMAY 2, 2016

And this is the Obesity Journal article  about the study referred to in the above article.

Original ArticlePersistent metabolic adaptation 6 years after “The Biggest Loser” competition

In conclusion, we found that “The Biggest Loser” participants regained a substantial amount of their lost weight in the 6 years since the competition but overall were quite successful at long-term weight loss compared with other lifestyle interventions. Despite substantial weight regain, a large persistent metabolic adaptation was detected. Contrary to expectations, the degree of metabolic adaptation at the end of the competition was not associated with weight regain, but those with greater long-term weight loss also had greater ongoing metabolic slowing. Therefore, long-term weight loss requires vigilant combat against persistent metabolic adaptation that acts to proportionally counter ongoing efforts to reduce body weight.