There's a secret to Nicole Richie's healthier new look — "The Simple Life" star simply underwent breast augmentation to round out her stick-thin figure.

"Nicole has worked hard to put on some weight, but she also got breast implants from a Beverly Hills plastic surgeon about six weeks ago," a source close to the actress told The ENQUIRER.

"The effect has been amazing. She looks great and feels great. And her new boobs have given her more confidence than she's ever had before."

The troubled wild child, who has been under medical treatment to add pounds to her 5-foot-2 frame, has been the subject of eating disorder speculation for the past two years. But in the last few weeks, she's emerged looking healthier and rounder than she has in years.

Not only has The ENQUIRER confirmed Nicole's breast augmentation with a well-placed source, but a leading doctor who examined photos of her agrees there is no doubt what's behind Nicole's sudden growth spurt.

"Nicole has gained a little weight, five pounds at the most — but her breasts have increased from AA to B, which is out of proportion to her relatively small weight gain," Detroit-based plastic surgeon Dr. Anthony Youn told The ENQUIRER.

Pick up this week's Enquirer for more!