The entire "Hefty Hanna" story is problematic. When we are introduced to Hanna, she's slim and popular. Flashbacks, however, show her as being overweight, constantly eating, and feeling miserable. She seems to be on the fringe of her friend group, people tease her about her weight, and Hanna never really feels like she fits in.
This storyline would have been more empowering if we could have seen Hanna learn to embrace her body and love herself. Instead, we see Alison — who mocks her and calls her "Hefty Hanna" — encourage her to purge after eating. Very little screen time is devoted to Hanna's recovery from her eating disorder, even though she's on the brink of a relapse more than once.
According to the U.S. Department of Health and Human Services, nearly three percent of 13 to 18 year olds are diagnosed with eating disorders. Eighty percent of adolescents and young adults who have been diagnosed with bulimia are female. Considering that Pretty Little Liars' target audience is young women, the lack of sensitivity displayed in this storyline is even more disappointing.