"[Then] I started throwing up to lose weight."
Demi also revealed she started self-harming when she was 12 years old and admits to "self-medicating" with drugs and alcohol.
She added in an interview with You magazine: "I started when I was 12, when I was bullied. It was my way of dealing with the stress and then I often resorted to it when I was feeling overworked.
"Girls [who self-harm] scratch or cut themselves with razor blades, scissors or sharp objects, or burn themselves. I've pretty much tried all of it. My main thing was cutting and that was so horrible.
"I definitely self-medicated with drugs and alcohol. I would be lying if I said I didn't."
Though Demi is now focused on her recovery, she is aware that she will be fighting her problems for the rest of her life.
She added: "There's definitely temptation - every meal I fight it. It's an addiction and I'm going to have to fight it for the rest of my life.
"There's no cure and I may mess up, but I want to be a better role model for my fans and my younger sister."
- BANG! Showbiz