The actress just went back to the basics to prep for her steamy scene with costar Ryan Guzman, 27.
"I eat right and exercise! I put in the work like everyone else," Lopez, 45, tells PEOPLE, adding that her regime includes circuit training, cardio and workouts by celeb trainer Tracy Anderson.
"You have to switch it up to keep your body and yourself fresh."
As for plastic surgery? The "Booty" singer says she's all natural – but she hasn't ruled out getting work done down the road.
"I haven't done anything. I don't know how I'll feel in 10 or 15 years. I deserve the right to feel how I feel at the time," she says. "This person [right now] doesn't feel the need to do anything …"
Adds Lopez: "I feel comfortable in my own skin, absolutely."
For more of this exclusive interview, and to see inside Lopez's amazing L.A. home, pick up the latest issue of PEOPLE, on newsstands now