Hi I'm 3 months diagnosed Gluten intolerant and am 2 weeks out from my 2nd Ironman (first gluten-free). I have sought to become "fat adapted" and think that it is working, my run times have dropped drastically (about 45sec/km in 3 weeks).
I currently use a small amount of a product called 32GI endure (1 scoop in a 700ml bidon) over the course of a long ride and have a banana about 1 hour in then 20grams of honey per hour following. I have found this works for me and have tested it up to a 150km ride with a 5km run off the back.
2 weeks ago I tested the above minus banana in a half ironman and took 18min off my time from the previous year despite carrying a calf injury and had no problems where previously I would have had 2+ toilet stops. I had 3 scrambled eggs 2.5 hours before the race.
Pre-workout I will have a FAT BLACK coffee, black coffee with 1 teaspoon butter and 1 tablespoon coconut oil.
There are a growing number of gluten-free athletes getting around the triathlon scene including Luke McKenzie who came 2nd at KONA Ironman World Champs so it is definitely possible to race well and be gluten-free!