Rachel Frederickson won The Biggest Loser, but her gaunt look and dramatic 155-lb. weight loss is sparking controversy.

In the new issue of In Touch, an insider reveals to the mag that Rachel frequented an infrared sauna, which heats the body using infrared radiation to burn calories and boost metabolism.

“She came in almost every day for two-and-a-half weeks before the finale,” the source at Firm Body Evolution in LA tells In Touch. “You can burn up to 600 calories in a half-hour session, although everyone is different,” the source explains.

Rachel quickly defended herself against claims that she went too far, but her explanation only fueled the fire. “I would take maybe three, four classes a day,” she says, revealing how she continued to lose weight on her own. “I’d be doing Zumba and then I’d go to spin class … [and] now I like to go running.” Rachel also confesses to consuming just 1,600 calories a day, spread over five small meals.

Despite the backlash, Rachel remains undeterred, insisting she’s healthy and happy. “I’ve never felt this great before,” she gushes. “I found that proud, confident girl that I’d lost. I truly found the person I want to be.”

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