01/18/2012 at 06:30 AM EST
Following a 20-lb. weight-loss thanks to two weeks of intense workouts at The Biggest Loser's Fitness Ridge in Malibu, Marissa Jaret Winokur let the holidays get the better of her.
"I started working out like a mad woman and eating healthy," Winokur, 38, told PEOPLE on Tuesday. "And then right before Thanksgiving, I was like, 'Oh, no, I'm starting to gain weight.' I can gain 20 pounds in a heartbeat."
But since 2012 began, Winokur and her Retired at 35 costar BFF Josh McDermitt have been each other's support system for shedding those nasty pounds.
"Being on set is really hard because there's craft service," Winokur says. "Josh and I have literally been like, 'We can't go to craft service without each other. We're like, 'I'm your sponsor. Come on, let's go.' We can't mess around. Craft service is a disaster."
Showing photos McDermitt has sent to her iPhone from popular L.A. nature sites, the 2003 Best Actress Tony winner explains, "We'll text each other in the morning [about our hikes]. Since the year began, I'm doing well. Everything's back on track."
Although the former Dance Your Ass Off host does not know exactly how much she has lost so far this time around, she knows she's off to a good start because her "clothes are fitting better" and "it's also a mental thing" where she doesn't "want to eat crap."
As she points out, craft services are "like being at a Vegas buffet with every food you've ever wanted" – but, "Like today, for example, I wanted a banana instead of s––y Chinese food."