"Really, I've never done anything where I've thought about my body as much. You are literally in a bikini the entire day," she tells the June issue of Women's Health. "I even wore a swimsuit when I auditioned with Zac."
In preparation for the movie, Daddario reached out to the man responsible for Efron's abs, trainer Patrick Murphy, and was ready to gain some weight in the form of muscle mass -- or as Murphy calls it, "visual lines of definition."
Daddario elaborated to ET about what it was like shooting scenes while wearing minimal clothing, and noted that body confidence is crucial when shooting a film like this. "I turned 31 recently, and through my 20s I learned that as a woman, being confident with how you look and how you feel is the most important thing," she said. "I think no matter what, there's always something that you're going to criticize about yourself. Confidence is attractive, and confidence is sexy."