The Biggest Loser winner Rachel Frederickson lost 150 pounds on the show, and everyone is raving about the quick weight-loss.

The latest news comes from Frederickson herself, who told People that she limited her diet to 1,600 calories a day and spent six hours a day working out in three months. "Maybe I was a little too enthusiastic in my training to get to the finale," she told People.

Keri Glassman, M.S., R.D., a member of Women's Health's advisory board and a judge on Cook Your Ass Off, talks about how working out for a whopping six hours a day can affect your body.

"1,600 calories a day is what many people need just for their bodies to function normally," says Glassman. By working out for six hours a day, Frederickson was burning anywhere from 1,000 to 3,600 calories, depending on what type of exercises she was doing.

When you have a deficit that big, it's likely impairing everything from cognitive function to immune function to bone strength, says Glassman.

While some athletes may work out six hours a day, they're also making sure to use proper form and refuel properly to stay healthy while maintaining such a demanding physical routine. "If you’re not being monitored perfectly, you could definitely be putting yourself at risk for injury," says Glassman.