Mischa in India
07/21/2009 AT 06:10 PM EDT
's personal demons not only included a DUI arrest
, relationship breakups and a hospitalization
at a psychiatric ward – the actress also struggled with a fluctuating weight and body image.
"She has big self-esteem issues. ... She hates her legs," says a source close to Barton. "She isn't comfortable with her body. It's been a big source of stress and self-hate."
Speculation about 23-year-old actress's weight and nasty comments from tabloids and blogs also fueled insecurity.
"She had a big problem with those photos of her cellulite. … She didn't like it," says another source. "That just was something that contributed to her spiraling but she didn't do much to fix it because of her partying."
While another friend tells PEOPLE the photos upset the former O.C.
star – "[She was] more pissed off than hurt and she complained a lot about that" – she didn't let them get "to her too much. ... I never saw her diet."
But when photos showed a thinner Barton, she took to her blog and spoke out about the "crazy press," telling fans that she's "happier and healthier than ever so there's no need to worry about me."
"Just be happy and secure with yourself," she wrote on her Web site
. "Don't let other people's perceptions of you dictate the way you live your life."
Reporting by DAVID CAPLAN, LISA INGRASSIA and ALYSSA SHELASKY