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OTRC: Demi Lovato opens up about eating disorders, depression and dancer scuffle

Demi Lovato appears in a promotional still for her '20/20' interview with Robin Roberts in April 2011.

Demi Lovato, who recently underwent treatment at a clinic, says in new interviews that bullying drove her to anorexia and bulimia.

The 18-year-old actress and singer also disclosed that she has bipolar disorder and did strike a backup dancer on her tour with the Jonas Brothers, as reported. Lovato left the tour in the fall of 2010. She underwent nearly three months of inpatient treatment and returned to her Los Angeles home in January.

Lovato told ABC News in an interview set to air on "20/20" on Friday, April 22 at 10 p.m. ET, that she was "compulsively overeating" when she was 8 and was often bullied about her weight.

"I literally didn't know why they were being so mean to me," she said. "And when I would ask them why, they would just say, 'Well, you're fat.' I developed an eating disorder, and that's kind of what I've been dealing with ever since. So, I guess, for the past 10 years I've had a really unhealthy relationship with food."

Lovato began restricting her eating. She developed anorexia and bulimia, which continued up until her tour with the Jonas Brothers.

"I was performing concerts on an empty stomach," she said. "I was losing my voice from purging. I was self-medicating. I was not taking medication for depression, and I literally was so emotionally whacked out that I took it out on someone that meant a lot to me."

She admitted to physically striking one of her backup dancers, Alex Welch, during the South American leg of her tour. Reports of the confrontation were leaked late last year, after Lovato checked herself into a medical center to deal with "physical and emotional issues." ABC News quoted the actress as saying: "I take 100 percent, full responsibility. I feel horrible."

Her family and management, Lovato said, "sat me down and said, 'You can't live like this.'"

Lovato told ABC News that she checked into Timberline Knolls - a residential treatment center in Illinois for women battling addiction and eating disorders. She said that at the clinic, she found inspiration to get better by looking at a picture of her 9-year-old half sister Madison De La Garza, who plays Juanita Solis on the ABC drama series "Desperate Housewives." De La Garza is overweight herself.

Lovato also revealed that she began dealing with depression when she was a child and began cutting herself when she was 11.

"I never found out until I went into treatment that I was bipolar," Lovato told People magazine. "Looking back it makes sense. There were times when I was so manic, I was writing seven songs in one night and I'd be up until 5:30 in the morning. I feel like I am in control now where my whole life I wasn't in control."

On Tuesday, April 19, a Disney Channel spokesperson confirmed Lovato would not return to her show "Sonny With a Chance." The actress, who had played main character Sonny Munroe since the show began in 2009, had said she wanted to focus on her music and that she didn't think shooting the series would be "healthy" for her recovery.

Lovato first spoke about her mental issues in mid-April and told Seventeen magazine: "I basically had a nervous breakdown."

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