For the interview, the actress -- who appears in the mag photographed in skimpy lingerie -- brings her own tabbouleh salad in a plastic container to a "deserted bar" that doesn't serve lunch so she can avoid temptation.
She says she's under a lot of pressure to be pin thin.
"If I didn't run and work out, there's no way I would be this thin," she recently told Glamour magazine. "But I have to stay in shape because I'm an actress. It's f----d up and it's twisted, but I wouldn't get the roles otherwise. If I'd been a bit bigger, I don't think they would have cast me for Mamma Mia!"
The stress has taken its toll. While talking to Esquire, Seyfried pops half a Lexapro pill (which treats anxiety) -- and a birth control pill (she's currently dating Dominic Cooper).