Actress Gabrielle Union revealed how she keeps her slim figure toned and tight. The "Being Mary Jane" star told Conan O'Brien that she gets her fitness inspirations from adult film stars and she is now on something she calls the "porn diet."

Union explained that she bases her fitness regimen off what she sees the porn gals who attend her gym do.

"I basically compete with them and they don't realize it. We are basically having the Olympics, they just aren't aware that we are in competition with each other," she told O'Brien. "I'll watch and see what they're ordering [at the gym's juice bar].

Union said she's noticed that most of the women she follows are vegans and don't eat meat. So how does the actress know these women are porn stars? She told O'Brien that she might have seen some of their work and she recognizes them.

She also dished on which celebrity she thinks has the best butt and Justin Timberlake's wife takes the prize.

"Jessica Biel has an amazing butt," she said. "But my daily butt inspirations are women at the gym."

The 40-year-old actress recently flaunted her toned figure in a two piece bikini while enjoying a beach vacation.

"Work hard... Laugh harder #urbancowgirl," she captioned the photo.

Even though Union credits her slim figure to stalking porn actresses at the gym, her trainer revealed to US Weekly in the fall of 2012 that Union does work hard to maintain her shape.

"With her body, she's a natural athlete," her trainer Ahmad Baari told US. "Depending on her schedule we'll do about three or four months that I will see her regularly, she'll leave and then come back and we work to get her back to where she wants to be. She tells me exactly what she needs."

"We try to keep it down to 90 minutes, each work out," he continued. "That includes stretching about 15 to 20 minutes before and after."

As far as her diet, Baari said that the actress eats lots of organic food.

"It's mind body spirit way of working out," he said.