When The Biggest Loser's Rachel Frederickson showed off her new 105-pound body on last night's finale episode, fans everywhere were completely caught by surprise.
The 24-year-old contestant dropped a total of 155 pounds from her frame, which equates to nearly 60 percent of her body weight.
The dramatic weight loss left several fans concerned, and also begged the question if her major drop in body weight would be manageable to maintain.
We tapped celebrity nutritionist Christine Avanti for her expert take on Rachel's transformation, who shed light on how miracle weight loss stories aren't always what they're cracked up to be.
"When I was watching the show last night, at first I didn't she was one of the contestants to be honest. She looked very very thin, especially from the waist up," she told us.
She wasn't the only one—fans around the country started tweeting their concerns immediately, and even Bob Harper and Jillian Michaels showed couldn't hide their shock on the show.
Avanti explains that it's risky for anyone to lose so much weight so quickly.
"They're pushing the envelope they're doing a lot more than what would be normal for weight loss...They're being monitored by a team doctors, trainers, psychologists, psychiatrists," she added. "We don't know [what is really going on]. It's a little scary."
And given that Frederickson lost the last 45 pounds in just two short months, Avanti has every reason to raise an eyebrow.
"I'd say half of that coming back in two to three months is very probable and that's not good. It's very damaging to her metabolic weight," told us, explaining that she prefers that her clients lose no more than 10 percent of their body weight per month.
Watch Christine Avanti discuss Rachel's dramatic weight loss on E! News tonight at 7 p.m. and 11:30 p.m.