  The rise in eating disorders, a condition with serious health complications,
has been linked to the proliferation of idealized body images on social media
platforms. However, the relationship between social media and eating disorders
is more complex, with online platforms potentially enabling harmful behaviors
by linking people to ``pro-ana'' communities that promote eating disorders. We
conceptualize the growth of harmful pro-ana communities as a process of online
radicalization. We show that a model of radicalization explains how individuals
are driven to conversations about extreme behaviors, like fasting, to achieve
the ``thin body'' goal, and how these conversations are validated by pro-ana
communities. By facilitating social connections to like-minded others, a shared
group identity and emotional support, social media platforms can trap
individuals within toxic echo chambers that normalize extreme disordered eating
behaviors and other forms of self-harm. Characterizing and quantifying the role
of online communities in amplifying harmful conversations will support the
development of strategies to mitigate their impact and promote better mental
health.
