The Scottish nutritionist said she had never watched the hit ITV1 show before because of her phobia of insects.
Mrs McKeith, 51, said: "It was like a horror movie that never ended. People are looking for this incredible explanation and I really don't have one. I liked the idea of going to Australia and thought I'd get a bit of a holiday.
"I didn't completely understand what I was getting myself into. I thought it would be an interesting way of challenging myself. When I finally realised what I was facing, I was absolutely mortified."
She also defended herself against claims she faked her fainting episode when she collapsed after being chosen to take part in a bushtucker trial, saying she had "a history of fainting".