"I spend a lot of time sitting in a car or sitting at a desk so when you're not keen on getting out and about in the first place, it doesn't help the situation," the show leader told the Herald.
"I would end up eating on the go a lot and the killer for me was stopping off for a latte at the petrol station.
"I couldn't pass a petrol station without getting coffee and I would often stop off half way to have a break and a latte," added the 44-year-old.
Monica's latte addiction has been hard to kick but she has swapped the caffeine for healthier herbal teas.
"I love lattes and really miss them, but I am trying to get into the habit of drinking herbal tea every day.
"But I still have the odd one," added the busy mum, who lives in Ballon, Co Carlow.
Single Monica, who is mum to Shauna (10) and Tadhg (12), is not only hoping to change her diet and attitude to exercise. She is also hoping to get her life back following her divorce 10 years ago.
Last week, Monica's two children prepared a meal for their mum, allowing her to relax and take up an old hobby.
Viewers watched last night as she went back to her old passion -- ballroom dancing, which she gave up 34 years ago.
"I am having a ball over the last few weeks," Monica told the Herald.