Duff, who has recently married hockey player Mike Comrie, revealed she was dangerously thin at the age of 17 because she let comments about her weight get to her.
The 23-year-old told Health magazine: 'I literally ate nothing but steamed vegetables and broiled or grilled chicken, with nothing else.
'I was touring all the time, travelling everywhere, and I felt so run down, not giving your body enough of what it needs is really dangerous, I regret it because I don't think I was happy then.'
She added: 'At the time, I felt almost proud of being skinny, but one day the mother of a fan came up to me and said, 'Are you OK? Are they not feeding you?'
'After that, all of a sudden, I stopped being as concerned about everything.'
Duff continued: 'It wasn't a big intervention or anything, I got off tour and changed - I started hanging out with my friends and cooking and had a more normal life.'