Kathryn, who has already started work on the new season, plans to match the contestants stride for stride and press-up for press-up.
"Generally I'll lose the couple of pounds once the show starts in January because you're seeing them being weighed in," Kathryn told the Herald.
It was revealed last week that Kathryn has split from her garda boyfriend of five years. The 33-year-old and Enda Waters separated during the summer but kept it quiet until now.
She has been busy working on The Voice since the break-up and will take on another series of Operation Transformation from January to March.
"I think it's like everybody after Christmas, you have slobbed around and you have eaten Christmas cake for four days in a row," she explained.
"It's a time that everybody over indulges and everybody, I think, understands when January comes and it's a new year."
Kathryn will be using the help of show fitness expert Carl Henry and nutritional whiz Dr Eva Orsmond to shed a few post-Christmas pounds.
"Once they all start back in January it definitely motivates me to go out for the runs and do the training with them.
"It will be nice to do Carl's exercises and start cooking Eva's recipes again."
Kathryn, who is just back from a trip to LA, is looking forward to getting her teeth stuck into the show.
She said: "I can't wait. What happens now is that we do this and all next week I'll be going around the country surprising the five and revealing the five leaders."