"I used to live, eat and sleep by an exercise schedule, and I couldn't enjoy myself if I didn't exercise. And then I realized, What a waste of time! My soft parts are probably never going away," the Letters to Juliet star, 24, tells Self magazine in its June issue.
She works out moderately, running for 30 minutes five days a week and doing pilates on the weekends. She's also not totally starving herself. "I mean, at the end of the day, if you can't have a Girl Scout cookie and a piece of cheese, what is life all about?" she asks.
Perfection in Hollywood is an illusion anyway, she says. "People may seem perfect, but that's because they spend thousands on trainers and diets and surgeries," she says. "If you have a negative body image, exercise, but not for your appearance. The main thing you can change is how you perceive yourself. Stop looking in the mirror and realize that you're living for yourself, not other people."
Asked if she has advice for young women struggling in their work, Seyfried points to her own career – and is clearly a bit skeptical about her sudden rise to prominence. "I've been an up-and-comer for so long," says the actress, who made her debut in 2004's Mean Girls. "Now everybody is telling me that I'm having 'a moment.' I'm like, 'All right, how long does that last?' "
She also talks about the tough decisions she's had to make between spending time with her family and with her boyfriend, Mamma Mia! costar Dominic Cooper.
"I just moved to New York from Los Angeles," she says. "I would have liked to live in London [where Cooper lives], but I felt it was better to be closer to my grandmothers, who are in Pennsylvania. They have always been a huge part of my life, and the longer I was in L.A., the harder it was. New York's a happy medium."