For an Ironman, the general principles are still pretty similar, however because of the increased duration, there’s a few key changes;
The amount of fuel is much greater. I still try to aim for 90-100g of carbohydrates per hour, but obviously that requires much more planning to make sure you carry enough fuel on both the bike and run. I tend to pour a number of the gels into a bottle and have that on the bike as its possible to store a much greater amount of carbs in a smaller volume, and then I will take water on course at aid stations to make sure I am keeping hydrated.
I also make sure that I carry some hydro tabs in a waterproof bag on the bike, so I can add them to the hydration system as I take water on the course.
Make sure you have a special treat… at some point in a full distance, it will get hard and you’ll get a slump in energy and motivation. Making sure you have something as a ‘pick me up’ is key to getting back on track. For me, it’s half a duo bar and a caffeine gel.
For the marathon run, fuelling is very important, however, I also think it is very much more to feel. Some days you feel great and can continue feeding as you would for a 70.3, and other times, due to exerting your body so much, your stomach may be feeling a bit delicate or you may be feeling lower on energy than expected. It’s much more about reading your body and adjusting accordingly, so I make sure I’ve got a range of gels, bars, and hydro tabs to cover most eventualities. This is very normal as every races is different and many factors can affect how you feel on the day.