Rachel Frederickson, 24, shed 155 lbs. in seven months to win $250,000 on The Biggest Loser, raising questions about the show's safety. Now she talks exclusively to PEOPLE in this week's issue about her extreme weight loss - and whether she went too far. Plus, former contestants speak out.

As a contestant on The Biggest Loser, Frederickson bared her 260-lb. body in nothing but a sports bra and shorts, shared her heartache about a bad breakup, and fought her way through dozens of grueling workouts. Still, nothing could have prepared the voice-over actress for the tidal wave of criticism and scrutiny that has engulfed her since revealing her 155-lb. weight loss on the reality show's Feb. 4 finale. "I am proud of my journey and excited for this new life," she tells PEOPLE. But she grows quiet when asked about the shock that registered on the faces of trainers Jillian Michaels and Bob Harper at the moment of her reveal, admitting that the overall response to her transformation has been "overwhelming. It's been quite a whirlwind."

It has also ignited the biggest controversy in The Biggest Loser's 15-season history, raising questions about Frederickson's health and the NBC reality competition's safety. Having dropped 45 lbs. in the three and a half months before the finale, the 5'4" Frederickson's winning weight of 105 lbs. puts her Body Mass Index at 18, just below what the CDC considers normal. Producers say she was carefully monitored throughout her nearly yearlong tenure with the show, including in the days before the finale. "Rachel passed all the required medical tests, ensuring she was healthy," says the show's executive producer Dave Broome. "The health and well-being of our contestants is our No. 1 priority."

Beyond the numbers, Frederickson's lined face and visibly bony arms alarmed many viewers, experts, and even some at the show - among them host Alison Sweeney, who tells PEOPLE, "I understand and shared in the concern for Rachel at the finale. My hope is that she and all show contestants achieve life-long health." Frederickson's trainer Dolvett Quince, who had last seen her when she left the Biggest Loser ranch in mid-October, says, "I was shocked. The first thing that went through my mind was, 'That's just too much.'" Frederickson concedes she "maybe was a little too enthusiastic" with her training. "I worked out six hours a day," she admits. But she insists she stuck to Quince's recommended 1,600 daily calorie allotment after leaving the ranch.

Asked point blank whether she has an eating disorder, she replies: "I am very, very healthy." Has she experienced any troubling signs of extreme weight loss, such as dehydration, a disrupted menstrual cycle or hair loss? "No. I've never felt better. I keep saying it: I am healthy."

But critics say The Biggest Loser's high-stakes format - rapid weight loss with a $250,000 pay-off for the contestant who loses the most - can be damaging. Kai Hibbard, 35, an outspoken opponent of the show who lost 118 lbs. as a finalist in season 3, says she was encouraged to "crash diet" on the ranch. She also says that when she told her trainer Kim Lyons that she wasn't sleeping and had stopped menstruating, Lyons advised her to "suck it up and get back on the treadmill." (NBC had no comment on Hibbard's accusations.) Lyons, who no longer works on the show, refutes the claim. Others take issue with the show's intense obstacle course-style workouts. "The truth is, the key to losing weight does not make for good TV," says celebrity trainer Harley Pasternak. "Taking 10,000 steps a day, eating smaller portions - how do you make a healthy smoothie exciting TV? It's impossible."

Now that the show is over, Quince wants to continue offering support to Frederickson. "We had the conversation about getting her body back to a place where she has energy and muscle mass," he says. "I'm not trying to lose any more weight," says Frederickson, who plans to scale back her workouts to around 90 minutes a day. As for her weight, "I'm just kind of finding where it all settles," she says. "I was a contestant, and I trained like an athlete for the finale. Now I am a girl in her real life."

More on The Biggest Loser scandal is featured in the 2.24.14 issue of PEOPLE, on newsstands now.

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