Taylor Swift has opened up about her struggle to overcome an eating disorder in a new documentary about her life.

Axar.az reports citing foreign media.

In Miss Americana, which premiered at the Sundance Film Festival, she said photographs and comments about her appearance had triggered the condition.

During her 2015 world tour, under-eating left her feeling "like I was going to pass out at the end of a show, or in the middle of it," Swift said.

"It's only happened a few times and I'm not in any way proud of it," she added.

Swift said she struggled with the condition for several years. Some days, she would "starve a little bit [and] just stop eating". The rest of the time, she kept lists of everything she ate and exercised constantly until she was a size double-zero (size two in the UK).