Diet Secrets of Gossip Girl Stars: "Good Underwear"

How do Gossip Girl stars like Leighton Meester and Blake Lively lose five pounds quickly?

"They don't. They just get some good underwear and they're fine," the show's costume designer Eric Damon told UsMagazine.com at the NYC party for his book You Know You Want It.

Take a look back at the hot fashions from last season of Gossip Girl!

"I say, just enjoy yourself. If you put on a couple of pounds, then great, buy some Spanx," Damon adds.

Damon says the spandex body shapers are just one thing he employs to ensure the female cast -- which also includes Jessica Szohr and Kelly Rutherford, who welcomed her second child seven months ago -- always look hot.

"There is a whole architecture system that happens on the show and on TV... that make your boobs and ass look great," he reveals.

But his chief concern is the young stars' comfort in their designer duds.

Find out who from Gossip Girl made Us' best dressed list this year

"There's a great give and take," Damon says. "If they want to say something about the outfit, I'm not some horrible designer that makes them wear this. If it's not making them look and feel great, that's fine."

Damon says it's the "most fun" to dress Ed Westwick, who plays Chuck Bass.

Check out which stars' bodies were talked about most

"It's amazing taking men's fashion, like Ed's character, to a dangerous place," he says. "He's a handsome man drinking bourbon, wearing pink -- it's a big movement for American men in fashion."