The 38-year-old is famous for her disapproval of overweight people and regularly makes her feelings on the issue heard on Twitter.
During Wednesday night’s episode of Celebrity Big Brother, Perez stripped down to his underwear while in the bedroom and Katie didn’t waste her opportunity.
She said: “He’s got more back fat than a blue whale.”
Previously Perez had been complaining to Nadia Sawalha about his loose skin, the result of extreme weight loss.
The blogger, 36, told Nadia that, even though he’s lost a lot of weight, he still feels fat thanks to the excess skin.
Katie has admitted that her views have changed slightly since filming her documentary My Fat Story, which involved her putting on weight for an experiment.
She said: “It’s definitely softened. I met a lot of people with a lot of things going on, I know people have their reasons.”
However she still insisted that, in a lot of cases, there are “no excuses”.
On her first night in the house, Katie was asked by Perez about her ‘trolling on Twitter’, but she dismissed his claims. She added: “I think I stand by freedom of speech.”