An insider at In Touch has also revealed that Rachel used an infrared sauna, which is known for burning calories and boosting metabolism.
“She came in almost every day for two-and-a-half weeks before the finale,” the source at Firm Body Evolution in LA told the mag. “You can burn up to 600 calories in a half-hour session, although everyone is different."
Previously, trainer Bob Harper, who did not work directly with Frederickson, said he was also shocked by her weight loss. Past winners have been supportive of Rachel, saying she probably did it for the $250,000 prize.
For more of Rachel's story, pick up this week's issue of People magazine, on newsstands Friday.