Most of the people think that you won’t finish your Ironman because of lack of training, but I tell you that the wrong nutrition can stop you faster and harder than you think.
Always exercise your intake in your training!
Eat 1 bar before starting the swim.
After your swim, just drink on the bike but not too much for the next 20 minutes. Then start to eat half of a bar per 20 minutes. So you should eat 300-400 kcals per hours. Better to eat bars than gels during biking.
Salt and magnesium
But some natural salt in your water (it should not taste salty), because then you have additional minerals (magnesium, etc.).
When you switch to running, maybe it’s better to also switch to gels than bars. This often killed me during running and a bowling ball was jumping around in my belly. Be careful when drinking Gatorade combined with gel. Maybe it’s better to just drink water. Eat 200-300 kcals per hour – less than during biking. Better to stock up before running.
If you tend getting cramps, then add enough magnesium to your nutrition. Do not drink more than 1-1,2 l (36-42 oz) of water or sport drinks per hour.
Last but not least: Always EXERCISE your nutrition / drinking habits in your training and not in the race!