Nicole Richie is seeking treatment for what her rep describes as an inability to put on weight.
"Nicole Richie has decided to undergo diagnostic treatment to determine why she's not been putting on any weight," her rep tells PEOPLE in a statement. "She is working with a team of doctors and specialists whose focus is nutrition. It is important to Nicole that she achieves this goal in a healthy way as this is not a treatment for an eating disorder."
Richie's thinness has been the subject of much debate – which she addressed
in May when she told Vanity Fair
magazine, "I know I'm too thin right now. I'm not happy with the way I look right now." She also said at the time that she was consulting with a nutritionist and a doctor, but blamed her weight loss in part on the breakup with her then-fiance, Adam "DJ AM" Goldstein.
"She's tired of everyone saying you don't eat, because she does," a source close to Richie tells PEOPLE. "She wants to gain weight. It wasn't anyone saying you have to go do this – it wasn't an intervention. It was her saying I'm tired of people saying this about me, I'm going to go get some tests. It was a personal decision."
Richie, 25, is starring in the fifth season of The Simple Life,
but production is on hold until she recovers, according to a rep for the show's studio.