Charles-Barclay said it took about a year for her small intestine to heal after making the necessary changes to her diet.
She is now fuelled by entirely gluten-free options.
“Three days out from racing I will start to carb-load with multiple bowls of rice, chicken and boiled eggs a day,” she said.
“During the race, I use gluten-free gels. I aim to consume up to 120 grams of carbohydrates per hour during an Ironman.
“I add additional electrolytes from salt tablets to my water bottles and I get my extra energy during racing and training from Red Bull.”
She is in contention to win the T100 Triathlon World Championship at the final race of the season in Qatar on Friday, 12 December.
Going into that race, Charles-Barclay, Canada’s Julie Derron and fellow Briton Katie Waugh sit within nine points of each other on the leaderboard. Charles-Barclay is third in the standings, seeking a big final performance.
“It’s going to be hot, it’s going to be tough, but it’s going to be a really exciting race,” she said.
But at least now she knows she how she needs to fuel, even if she has to take a mind-over-matter approach to some aspects.
“I have to eat rice multiple times a day for like three or four days going into the race,” she said.
“By the time I get there, I don’t want to see rice again for a while!”