The 'X Factor' USA judge says checking in to a treatment facility to help her overcome her struggles with bulimia and self-harming in 2010 was a life-changing move, especially because it proved who actually cared about her.
She told Company magazine: "A couple of months before I went to rehab, I had a birthday party, and there were a couple of hundred people there. It was full of people who I considered my closest friends.
"When I turned my phone on after being in rehab for three months, I expected lots of text messages and phone calls. I had four texts. That was a wake-up call."
The 20-year-old singer - who used to be friends with her fellow Disney stars Miley Cyrus and Selena Gomez - has cut most of her old pals out of her life and now only has a small support group of people she can rely on.
Demi added: "I don't have loads of friends. I used to, but then I realized, do any of them actually care?
"Now I have people who, if I break my leg in the middle of the night, will come to the hospital with me. Or they'll answer the phone at 4 a.m. if I need them."