Britney: "I'll Starve Myself!"

(wireimage.com)

UPDATE: Only hours after being ordered to undergo drug and alcohol testing, Britney was out and about on the L.A. club scene, first hitting up Winston's nightclub with her cousin Alli Sims and fellow pop star Avril Lavigne, and then moving on later to Hyde. More to come on this one...

As the judge in her custody battle with ex-hubby Kevin Federline orders Britney Spears to undergo testing for drug and alcohol use, OK! can report that friends of the beleaguered pop star are worried sick that her starve-and-bing relationship with food may be pushing her even deeper into despair.

"Britney told me, 'I'll starve myself because I'm fat,'" one friend of the singer reveals to OK!. "She kept telling me she thought I was fat and disgusting."

For all the details on Brit's dangerous diet habits, pick up the new issue of OK!, on sales Thursday.