The 27-year-old, who became a household name after he and his other half won the latest series of Love Island, said he was left gobsmacked by the body analysis.
Speaking to BBC Sport, he said: "It's strange because when you think of obese you think of someone who can't move. But I can go on a run – I'm fit."
And while he wouldn't class himself as "obese", Jack, who is currently taking part in a 12 week transformation, admitted that he's easily led astray by Dani's suggestions to go for a curry.
He said: "There have been times when I should probably get in the gym but if Dani goes, 'Shall we get a curry and stay in and watch a film?'
"I have to think about what's more interesting."
His comments come as the ITV2 reality star, who is preparing for a charity boxing match in March, posted a throwback snap from three years ago showing off his washboard abs.
The reality star looked very different now after shooting to fame on the dating show alongside girlfriend, Dani.
In the snap Jack is wearing a pair of baggy blue shorts and trainers as he grins for the camera.
Standing in what looks like a gym changing room, the 27-year-old captioned the post: "Happy Sunday from the 2016 me … #sixpackjack 😎 Throwback Sunday".
Sporting a deep tan and floppy hair, the former pen salesman looks very different to his current self-confessed dad bod.
His fans couldn’t believe their eyes as they rushed to comment and like the post.
While some of his fans got confused and thought he had slimmed down overnight, most followers rushed to tell the celeb he looked far better now.
One gushed: "Without downplaying the amount of work that obviously went in to the body in this pic, you look so much more handsome now lovely xx".
While another added: "prefer the dad bod". One user commented: "I prefer him now me."
The post comes just days after Jack confessed to girlfriend Dani Dyer, 23, that he’d taken cocaine on a night out.
After apologising to his fans, calling it a "stupid, stupid mistake", he made sure he was back in Dani’s good books.
The couple reunited when the reality star returned from Africa where she'd been filming for Comic Relief ahead of her Mount Kilimanjaro climb for charity.
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