Before setting up camp, the 34-year-old weighed around 19 stone and estimated his food intake at roughly 4,000 calories a day.
In the jungle, he claims to have eaten just 250 a day, telling the Sun: “That is starvation. That was the biggest shock.”
Describing the “physical ailments” he suffered, James added: “I had nothing in my legs. I’ve never had a panic attack before.
“It felt like I’d done leg weights or 100 hill sprints and I’d get up and go dizzy. I’d have to hold on to the tree and hold myself up. I’d walk 25 steps and be heavy breathing.”
James was voted out of the show on Tuesday night and shortly before reuniting with his wife Chloe Madeley, he told Ant McPartlin and Declan Donnelly his body had started to “shut down” on the show.
“I was burning a lot of calories with all the adrenaline and the walking to the trials,” he said. “In the evenings and afternoons I couldn't really focus, I had nothing in my legs and I was getting really tired.
"I didn't want to overly complain but I really struggled. Everyone in the camp was so kind to me...they all gave me a little spoonful of their food here and there."
James's time in the jungle was largely positive as this year's batch of camp mates quickly bonded and built friendships.
However, he did leave viewers smirking after one clash, which saw him rant about people being "unintelligent" before stating he was going to watch everything "umplode."
I’m A Celebrity continues at 9pm. The grand final takes place on Sunday.