This is an issue close to my heart, well, my stomach actually! I'd had almost EVERY Ironman race plagued by stomach issues. Let me be clear here, I'm not talking just cramps, I'm talking hiding in the bushes mid-run, visiting EVERY portaloo along the course for 26 miles type issues. It's been horrific. So, trust me when I say you NEED TO PRACTICE YOUR NUTRITION.
I fell foul of the golden rules and tried to overload my carbs to the max. I hadn't practised this volume in training, I'd come close on my log runs and rides, but not to the extent I'd tried in the race. Major NO! I would never tell my athletes to do this, so why did I try this myself?! - Ironman Crazies?!!
So, here are my nutrition rules that you MUST abide by to give yourself the greatest chance of success and the least chance of toilet stops?
EXPERIMENT. Do this early in the season - even as early as your winter training. Try lots of different brands, types (gels, chewies, bars etc) and see what feels best in your gut. Keep a little diary note after each session so you can remember and refer back to how you felt on each test.
EXPERIMENT SOME MORE. You might have found what you think is the right product, now try it at different intensities. Your digestive system is under different pressures and has varying resources at each intensity level of exercise, so what might work under a long easy ride might not work if you're pushing hard.
CHANGE POSITIONS. You might train on the road bike but race on your tri bike. The positions are very different and the aero position is very restrictive. Make sure you test long rides with you nutrition on your race bike.
INCREASE THE CARBS. Think you've found the answer? Start to increase the amount of carbs you ingest per hour. You might find that your body has a limit of say 60g per hour. Keep diary notes as to how much you can ingest and how you feel during and after. Do this at different intensities.
REMEMBER TO TAKE WATER. Don't forget to drink pure water too - that's water that's not mixed in with carb powder. Add some electrolytes too.
TEST IN DIFFERENT TEMPERATURES. If you're racing in hotter or colder climates than you're used to, then test your nutrition in these conditions as your digestive system will work differently and your body will demand energy and hydration in different levels than you're used to at home. Don't expect to consume the same on race day if you've trained in the UK and you're racing in Spain!
COURSE NUTRITION. Research the nutrition that will be provided on course, order some and try it.
EXPO EXCITEMENT. You might taste some new and exciting flavours or a new brand of nutrition in the expo pre-race. Do not be tempted to switch to this for your race tomorrow! By all means buy some to take home with you (and test!) but do not try anything new on race day!
So let's summarise. PRACTICE!! That's basically it.
Once you've found something right, you can start to try to train your gut to take more carbs per hour. But, make sure you've cracked the basics first.
Precision Fuel and Hydration offer a great fueling strategy, but take it with a pinch of salt (!!) and test it out, it's a great starting point - remember, everyone's different!