When Jessica Jochim returned to work after her three-month maternity leave, she was the envy of her co-workers at Babies "R" Us. Jochim, who had gained 40 pounds carrying her first child, steadily slimmed until she was a size 4 again. Yet, exercise was a pre-baby relic. She wasn't dieting, either. In fact, every two hours, she snacked as if on cue.

What was her secret? Breast-feeding her newborn James on demand, and using a breast pump to take milk home to him.

"All the ladies at work started joking they were going to go in back and pump so they could start losing weight like I was," said Jochim, a mother of three from Vancouver, Wash. "I had a baby suckling 600 calories a day out of me."

That breast-feeding gives mothers an edge shedding baby weight has long been suspected. But lately, a parade of celebrities has attributed their postpartum slimming to nursing, bringing this age-old topic back into the spotlight. Adding to the conversation is a large study that suggests that weight loss through breast-feeding is not a myth.

Earlier this year, Rebecca Romijn, who wore a shrink-wrapped outfit in "X-Men," called breast-feeding her new twins "the very best diet I've been on." After Angelina Jolie posed for the November 2008 cover of W magazine nursing one of her twins, she said that it had helped her regain her figure. (That cover made her an icon among breast-feeding advocates and inspired a bronze statue of a nude Jolie double-nursing her newborns that was exhibited in London last month.)

These days, more than ever, a mother is expected to bounce back from pregnancy and be a "yummy mummy" in no time. Skin-care lines like Mama Mio target mothers with firming creams like Boob Tube. Nursing mothers can buy form-fitting tops at YummyMummyStore.com so they can flaunt their shape as they push their Bugaboo.

Is it any wonder that some new mothers are quietly thrilled at the calorie cushion that breast-feeding provides? "Nobody wants to admit they are doing it for themselves, or 'I'm doing it to help myself look hot again,'" said Jesse Comer, from Portland, Ore., whose main motivation to breast-feed was her baby's health. "It's tough to admit to other people that everything isn't about the baby." But Comer, like many mothers interviewed for this article, "felt like until the weight was off, I wouldn't feel myself."

For those incredibly shrinking women, the time they nurse is precious not only for its skin-on-skin cuddling, but also for the Get Out of Dieting Jail Free card that comes with it.

But does breast-feeding actually speed weight loss in postpartum women? It depends.