During this moment of weakness, O'Brady says he ate around 2000 calories of his rations - dubbed 'Colin Bars'. The Colin Bars were high in fat, formulated to ensure he had enough energy for the intense hiking.

They were not made to be eaten in a late-night binge.

The next day disaster struck - having already packed up camp and dressed in his gear O'Brady could not stop to use the toilet. His stomach was cramping and he was in pain, but he thought he could make it.

Six miles into his 12-mile day, the inevitable happened.

"I thought that I'd get some relief if I was able to pass some gas, so I tried," he wrote.

"Unfortunately more than gas came out."

O'Brady only packed one pair of underwear for his trip, to minimise the weight of his sled as much as possible.

"I bring 220 pounds of food but one pair of underwear," O'Brady told Business Insider before he left for his trip in 2018.

"I'll be filthy at the end!"

At the time, he had no idea just how true those words would be.

He described the unfortunate accident as "very humiliating" in his book.