The 27-year-old, who plays iconic 1970s adult movie star Linda Lovelace in the new biopic, was comfortable getting naked on camera and didn't undergo a strict exercise regime or diet before filming began, reported Us magazine.
"I felt liberated. Growing up I was made to think nudity was wrong because it was censored in movies but it was like, 'what's the big deal? I run every day and I try to eat well. Linda was thin but if I stopped eating, I'd just look gross," she said.
Seyfried also revealed she and co-star Peter Sarsgaard enjoyed a dinner together to get over any awkwardness before filming their intimate scenes together.
"We had a dinner before filming and we talked about why he decided to do the film. I think his wife, Maggie Gyllenhaal, convinced him to do the role."