Britney Spears has confessed to doctors that she has been suffering from the eating disorder bulimia since she was 16.

The 25-year-old singer tearfully told rehab staff - already treating her for drug and alcohol abuse - that she "pigs out" on junk food like burgers, sweets, biscuits and ice cream then makes herself vomit to avoid putting on weight.

Britney's nine-year nightmare, revealed in an American magazine, was confirmed by a senior source at the £24,000-a-month Promises centre in Malibu, California.

She entered the centre last month after shaving her head at a hair salon.

"Doctors are alarmed at the physical state she is in," said the source. "They confronted her about her desperately unhealthy lifestyle and the truth came pouring out."

Britney said she managed to stop the dangerous habit during her two pregnancies.

But as soon as sons Sean Preston and Jayden James were born, she began the desperately unhealthy cycle again in an effort to lose her added baby weight.

On top of her alcohol and alleged cocaine use, the bulimia turned her into a "human wreck", according to the source, who added: "When she came here she was shaking and baking. Her whole body was wracked by spasms and she was hot one minute, then freezing cold the next.

"Her first week in detox was real hell. She was in a total mess but slowly she's pulling through."

Dietary specialists at Promises are working with doctors to help Britney conquer the eating disorder - famously suffered by Princess Diana - which was discovered when specialists realised why her medications were not working.