Kim Kardashian: I've been following the Atkins diet

New mama Kim Kardashian has been wearing some pretty curve-hugging outfits lately, and now we know how she's gotten back in shape post-baby. It turns out the reality starlet has been following the low-carb Atkins diet.

"I've actually been doing the Atkins diet & luv it," she tweeted on Sunday in response to a fan's desire to know how Kardashian lost the weight after giving birth to daughter North West on June 15.

An Atkins executive told us that Kardashian, 32, started the program in June after getting approval from her doctor.

 "Kim Kardashian wanted a balanced and effective way to lose weight following her pregnancy and she chose Atkins. She ate lots of lean proteins, veggies, fruits, and healthy fats like avocado and nuts," said Colette Heimowitz, vice president of nutrion for Atkins Nutritionals. "She experienced previous success on the plan, and knew she needed something that works."

Kardashian has been supplementing her dieting with exercise.

On Friday, she and boyfriend Kanye West were spotted taking an early morning class at Barry's Bootcamp in Sherman Oaks, Calif. According to our spy, the reality starlet put a "lot of effort" into the class.

"They looked great -- especially for 6 a.m.," the spy said.