Jessica Alba's Weight Loss Secret: A Double Corset

Jessica Alba is revealing her secret to getting her famously toned body back after giving birth to two children -- wearing a double corset for three months.

"I wore a double corset day and night for three months," Alba tells Net-A-Porter magazine. "It was sweaty, but worth it."

Pics: Jessica Alba's Colorful Day with Kids

Though she does admit that the method is painful.

"It was brutal; it's not for everyone," she says.

Though Alba has recently become a best-seller author thanks to her book The Honest Life, the 31-year-old actress isn't giving up her day job -- she tells the magazine that she's particularly proud of reprising her role as Nancy Callahan in the Sin City sequel, Sin City: A Dame to Kill For (out October 4).

Video: Jessica Alba Fashion Flashback

"I just finished the best movie I’ve ever done," she says about the highly anticipated film. "It was so opposite to what I do [at home]. My approach to acting now is so different – I'm fearless because I have nothing to lose. Before [children] my identity was wrapped up in every decision – now, I don't care. It could be a pile of s**t and you could think it was the worst thing you ever saw, but I still had the best experience."