Nicole Richie

Nicole Richie, daughter of R&B singer Lionel Richie, checked herself into a treatment facility in hopes to find answers to why she is unable gain weight.

A spokeswoman for ?The Simple Life star? TV star said: "Nicole Richie has decided to undergo diagnostic treatment to determine why she's not been putting on any weight. It is important to Nicole that she achieves this goal in a healthy way as this is not a treatment for an eating disorder."

The spokeswoman added that Richie was "working with a team of doctors and specialists whose focus is nutrition".

Despite knowing she is unhealthily underweight Richie is adamant that she does not have an eating disorder, she said on her Myspace page recently: "I don't know why or how this rumor started, but I am home, in LA, and very happy. I do not have an eating disorder, and I don't know how many times I have to say it."