Heidi Montag is a dirty, dirty girl on the cover of the September issue of Playboy magazine, but the reality TV star says it's all in good taste!

"I'm very religious. I'm a big Christian girl," Montag tells "Extra." The 22-year-old newlywed adds, "I kinda wanted to keep those values a little bit." Heidi reveals her conservative father, Bill, doesn't know his daughter bared all for Playboy. "I haven't told my dad yet," she says. "I might not tell him."

Mom, however, gave Heidi a thumbs up! "My mom was so excited she was just, like, pose! God gave you that body, you show off that cute little thing," Montag said with a smile.

The paparazzi magnet also talked about her intense workouts prior to stripping down for the magazine. She confessed, "I love food, too, so I have to work out."

Check out Heidi's "Hills" in the new issue of Playboy -- on newsstands Friday.