From PEOPLE Magazine Click to enlarge
NOW! SIZE 8

When Jordin Sparks first hit the American Idol stage in 2007, at age 17 and size 14, she flinched at the thought of wearing anything sleeveless. "I like to wear sleeves because they cover up my arms," she told PEOPLE at the time. Fast-forward to 2011, and a more confident Sparks has no trouble revealing much more than her arms: In February she stepped out in a sexy black backless dress. "I wore it without Spanx!" Sparks says. "I was so excited." And now, after losing 30 lbs. in four months, Sparks has gone even farther-revealing her new trim, size-8 figure in her first-ever bikini photo shoot. "Before, if I were to wear a bikini, it would just be in front of my mom or really close friends with a coverup," says the pop star, who credits eating smaller portions and taking Zumba, the popular Latin dance-inspired cardio class, for her "sexier" silhouette. "I feel good! I love that I still have my curves. I definitely didn't want to lose those," she says, adding, "I don't want to lose more weight. I just want to tone. I'm in a really good place now."

When the 5'11" Sparks left Glendale, Ariz., where she grew up, for Los Angeles to compete on Idol, she quickly realized, "Hollywood large is so different than real-life large. Everyone was so much smaller than me. I looked massive next to Ryan Seacrest! But I was lucky that I've never had anyone say, 'Jordin, you need to lose weight.' And it wasn't because I didn't like myself that I wanted to change."

The real impetus came before her 21st birthday last December, when Sparks came down with pneumonia and decided that "I couldn't take my health for granted anymore." She started going on hikes and doing 30 minutes of high-impact cardio before getting hooked on taking hour-long Zumba classes up to five times a week at Gold's Gym. "The weight just fell off," says her instructor Nichet Smith. "She crossed over from a teen into a woman." Next Sparks changed her eating habits (see box). If her mom whips up her famous sweet potato casserole, Sparks now limits herself to one serving instead of two, and "I decided not to eat for two hours before I go to bed," she says. Now when she checks out her reflection in the mirror (usually in outfits that are "a little bit tighter and a little shorter"), Sparks says, "I see the change in my face and neck." Others are noticing too. "I'm standing up a little bit straighter because guys are staring," she says. "I'm loving it."