Unlike some new moms, Mariah Carey is more than happy to show off her post-baby body. The songstress, who gave birth to twins nearly one year ago, flaunts her abs on the May issue of Shape and reveals some of the weight-loss secrets that helped her shed 30 pounds in just six months.While pregnant with Moroccan and Monroe, "I put on around 70 pounds," Carey, 42, tells the magazine. "But if you look at photos of me when I was pregnant, you'd say, 'Wow, she gained 9,000 pounds!' A lot of it was water weight because I pretty much had head-to-toe edema, which is very painful. Luckily, all the swelling went away fairly quickly after the babies were born. Then I had about 30 more pounds to drop. I have such empathy for people who need to lose a lot of weight, because I know what they're going through. I remember thinking at the time, 'I'll never look or feel the same again.'"Carey — who poses for the magazine cover in a bikini bottom and striped, off-the-shoulder top — selected Jenny Craig to help lose the rest of the weight because she liked the way their program, which she started last July, is structured. (She's a big fan of the brand's meals, especially the soups, but prepares a lot of her own food at home.) In November, it was announced she had become the company's brand ambassador and her first commercial aired in December. "I used to be able to slim down just by exercising more, but that's changed," she says. "Since having the babies, I realize that 90 percent of losing weight is my diet."… Read Mariah's full interview in the May issue of Shape, on sale April 23