Fergie: I Gained 17 Pounds With Penelope Cruz

When the director of Nine suggested Fergie and Penelope Cruz gain 17 pounds each before shooting began, they were happy to oblige.

"We were eating our brains out. We ordered everything fried and full of fat and salty," Fergie tells the July issue of Allure.

See stars' dramatic weight changes for roles.

But after filming wrapped, the singer, 34, lamented about not being able to fit into her skinny jeans – and the constant pregnancy rumors thanks to her new curves.

"If I don't do sit-ups, my stomach sticks out," Fergie explains. "Legs are easy for me. That's my lucky spot."

See Fergie's style evolution over the years.

Still, the weight stuck when she tried to lose it on her own.

"It was a very gradual thing, getting back into it and finally letting a trainer train me," she says. "I didn't want to be told what to do, and I wasn't mentally ready to crack the whip.

Find out other stars' workout plans.

She hired husband Josh Duhamel's trainer to run her through two-hour sessions several times a week.

The first 30 minutes of each session is spent getting Fergie out of bed.

"I'm a procrastinator," she admits. After she's awake, they lift weights, go hiking outdoors and jump rope – which, she jokes, requires three sports bras.

See Fergie's weight ups and downs.

Fergie isn't being too hard on herself: "I'll be happy with whatever body that brings me."

See more pics from Fergie's Allure shoot.

The Black Eyed Pea also opens up about sex after marriage with Duhamel, whom she wed in January.

"Nothing's changed in that department. I like to have fun in my costume onstage; why wouldn't I in the bedroom?" she teases.

See what Fergie – and other stars – looked like before they were famous.

They keep it hot by role-playing: "Oh, girl, I've got a big chest of fun little numbers, one that I would never wear in public," Fergie says.