The 24-year-old appeared gaunt during her big reveal, where it was announced that she had lost over 150 pounds over the course of just seven months.
The first sight of Frederickson, who dropped over 60 percent of her body weight, left viewers and trainers Bob Harper and Jillian Michaels stunned by dramatically thinner frame. (Just look at their reactions below.)
The weight loss caused an uproar of criticism saying that Frederickson was simply too thin, while some people speculated about whether it was even healthy.
Frederickson won $250,000 during the live season 15 finale on Tuesday, Feb.4.
"I feel amazing. I feel truly alive and just transformed," she told E! News shortly after learning that she was the winner of the weight loss competition show.
"I couldn't be more happy, more thankful to get this second chance to take charge of my life again."
But Frederickson isn't the only dramatic transformation that The Biggest Loser has seen.
In fact, over the past decade the show has featured hundreds of contestants—some of whom have lost over half of their initial body weight.
Let's take a trip down memory lane and look at some of the most shocking Biggest Loser before and after pics!
(E! and NBC are both part of the NBCUniversal family.)