Model and cookery book author Rozanna Purcell has spoken about how her sister Rachel's cancer diagnosis changed her outlook and spurred her to seek help for her eating disorder.

The sisters appeared on Friday night's Late Late Show where 28-year-old Roz said that up until about five years ago she measured her worth in how much she weighed and thought "the better version of me was a smaller Roz".

She said she felt "very much stuck and controlled" by how she looked and that was "the number one priority" in her life.

When a photo of her in underwear and a slip taken a number of years ago was shown on-screen, the social media star said: "When I look back I am very sad because I wasted a lot of time because I thought I wasn't good enough."

Everything changed when her sister Rachel was diagnosed with chronic myeloid leukaemia about three years ago. 

They spoke about why life is for living and not just about a number on the scales.

Watch the full interview on the RTÉ Player.

The Late Late Show airs on Friday nights at 9.35pm on RTÉ One.