For years Ashley Tisdale acted like many young women who are naturally slim: She ate junk food whenever she wanted and avoided the gym whenever she could. That all changed a few years ago when she injured her back on the set of The Suite Life of Zack & Cody. "It was a bad fall, and it really started hurting when I was dancing on tour," says Ashley. "In order to get my back stronger, I knew I had to strengthen my core." Despite being active on the job, Ashley had a real aversion to the gym. "I hated it!" she says. "I loved performing in the High School Musical movies—that didn't seem like work—but the gym felt like torture!" To improve her outlook, she focused on the health benefits of exercise. "Now before I work out, I think, 'I love exercise'—and it works," she says. Having such a positive attitude made it easier for Ashley to improve her diet when she learned about her family history of diabetes. "After I found out my grandfather has it and my mom is borderline, I knew I had to get serious about my diet too," says the 23-year-old actress/singer. "I realized just how much exercise and eating right make a difference in how you feel now and when you get older."

Ashley spoke to Shape exclusively about these changes and how they've not only benefited her body, but also given her a healthy dose of confidence.