For Alexandra Daddario, she had to pack ON the pounds to get her beach body ready for "Baywatch."

The gorgeous and super-fit actress will soon be strutting her stuff on the beach when "Baywatch" is released later this month, but rather than sliming down to fit into that iconic red swimsuit, she actually started eating more to gain weight and muscle mass.

GSI

"It was kind of amazing, the transformation I went through," she told Women's Health. "For 'Baywatch,' I started doing weight training, which I had never done before, and I saw a huge difference."

The 31-year-old said she used co-star Zac Efron's trainer because "Zac's body is insane" (no argument here!).

To prep for the role, she worked out four or five days a week for an hour each time. The high-intensity workouts consisted of free weights, sliders, TRX straps, resistance bands and BOSU balls.

Sometimes she worked out so hard that she got nauseous. But, it was worth it.

SBMF / MiamiPIXX / FAMEFLYNET PICTUR / Fame Flynet

"The ongoing joke is that everyone in the movie is supposed to be supernaturally attractive," she said. "Really, I've never done anything where I've thought about my body as much. You are literally in a bikini the entire day. I even wore a swimsuit when I auditioned with Zac."

Although the movie wrapped last year, Alexandra still works out with the same trainer.

"For the first time in my life, I have real abs!," she said.

VEM / FAMEFLYNET PICTURES / Wonderwall

Pre-"Baywatch," Alexandra, who has been linked to Zac, said her main workout was hot yoga, which she still believes in.

"I feel like it helps with anxiety, it helps with sleep, it was sort of more of a mental thing," she said.

Her diet, she knows, is as important as ever when it comes to leading a healthy life.

"As I've gotten older, something that made a huge difference for me was being healthy," she said. "It's not about how much you eat…it's eating healthy food and eating when you're hungry, and not thinking about it so much."