The 21-year-old model told the Diary how she will be ditching the diet this weekend as she gets into the festive spirit early with an action-packed social schedule.
"I'm going to Galway on Friday for my friend's birthday. They have an amazing Christmas market there with mulled wine so it's going to be great craic," said.
"Then on Sunday, myself and Cian are having our 'date day' because he doesn't get that much time off so we're going to do loads of fun stuff. We're going to go out for breakfast and lunch and then dinner at Trocadero.
"I've heard great things about it but I've never been there and there's apparently a picture of my granny Terry (Keane) on the wall. My mum said when she goes in, she always sees it and I've never seen it so that will be lovely."
Smitten Cian and former Miss Ireland Holly first met last December at a protest march against the Clontarf Flood Defence proposals but she explained how they didn't make things "official" until a month later.
"We were just starting to go out this time last year. We spent all of last Christmas together but we weren't officially together so it's nice this year to do presents and everything," she continued.
"We spent last New Year's Eve in Harry Byrne's in Clontarf and it was so awkward for the countdown, we just kind of high-fived each other.
"To be honest, I don't like going all out for New Year's Eve. I'd rather go to a local pub in a Christmas jumper and just chill out."
The granddaughter of the late social columnist Terry Keane will be enjoying a traditional Christmas at home with her family as she forsakes her strict Paleo diet, which mimics the eating habits of our caveman ancestors, in favour of some festive treats.
She has dropped a dress size over the past six months, thanks to a gruelling exercise regime with and healthy eating.
However, she admits she will be indulging on December 25.
"On Christmas Day, we'll go up to Howth for Mass in the morning and then we go to a relative's house where we all bring different parts of the meal. My dad usually does a pub quiz and we have karaoke so it's just a good laugh.
"I actually can't wait as when you come up to Christmas week, you're so tired. Everything just catches up on you.
"Usually I hate when it's quiet work-wise but this is nice because everything's all wrapped up."