Fueling for an IRONMAN

There's a lot to take in!

We often joke about nutrition being the 4th discipline of triathlon, and in an IRONMAN, your nutrition can make or break your race because our muscles can only store a finite amount of glycogen. The reliance on glycogen as the source of energy increases with intensity so the harder we are working the faster we will run through this store. For anything longer than two hours, the scientific community agrees that the ingestion of exogenous (we need to eat it) carbohydrates improves performance either by providing the fuel for additional energy or sparing the muscle and liver glycogen stores to prevent fatigue. Carbohydrates is key.

I want you to understanc how much carbohydrate we should aim for and why, which carbohydrates (because the type of carbohydrate is important), considerations when deciding on your fuelling strategy, a little bit about hydration, and finally, what the science says about carb loading and your pre-race nutrition. For good scientific sports nutrition information, I direct my students and athletes to follow Asker Jeukendrup on Instagram and through his website. His key messages are distilled down into easy to understand infographics and you can always read his blog posts for some deeper understanding.

The research

Most recommendations that you might have come across suggest somewhere between 30 and 60 g per hour of carbohydrates. This recommendation is based on findings that the maximal rate of oxidation (speed our bodies can turn it into energy) of any type of carbohydrate is 1 g per minute and the rate limiting step appeared to be absorption from the intestines into the blood. An important point to note here is if you provide more than 60 g per hour of glucose for example, then the extra glucose that can not be absorbed, will accumulate in the intestines, and this tends to upset the osmotic gradients between the blood and the intestines, so promotes gastrointestinal upset and that sloshy gut feeling as water can be pulled into the gut or has no drive to be absorbed. The reason for the big range in the ACSM recommendations was to allow those who struggle with gastrointestinal distress to find a somewhat happy medium between not fuelling at all and rapidly becoming fatigued and having to deal with multiple trips to the loo.

Asker and a colleague Aitor Viribay however have demonstrated in studies of cyclists and runners, and there is anecdotal evidence from Kona as well, that much higher amounts of carbohydrates can not only be tolerated but result in better performance as well. New recommendations from a consensus statement are now up to 90 g per hour of carbohydrates. But wait you said that if I had more than 60 g per hour it promotes GI issues? What the research shows is that if we use two different types of carbohydrates that rely on different transport proteins to get from the intestine to the blood then we can increase the absorption of total carbohydrates and therefore the conversion of carbs to energy. This is the basis behind the 2:1 ratio of glucose to fructose you might see advertised on some sports drinks or gels. Glucose is carried across by one transport protein (SGLT1), while fructose relies on a different one (GLUT5). We want more glucose because glucose is our bodies preferred energy source and its super easy to turn into energy. And it doesn’t matter if its in the form of glucose, sucrose, or maltodextrin, it appears to behave the same way. Fructose is harder to turn into energy and must go to the liver to be modified first but this may also have its benefits because the mixture is providing a fast burn and a slower burn form of energy.

In the process of doing all this research, it was also investigated whether the form of carbohydrate ingestion mattered. The researchers used sports drinks, gels and a low fat, low protein energy bar with matching carbohydrate profiles. It was shown that this tended to make little difference with only a slightly slower absorption seen from the energy bar, which was attributed to the small amounts of protein and fats in the bar. So it doesn’t actually matter how you consume it as long as you are getting up to 90 g per hour of a 2:1 mixture of some type of glucose and fructose. I will put here that if you are opting for the real food strategy of fuelling (which is totally an option) then be aware that the higher the fat, protein and fibre content of your fuel source the slower the absorption will be and so it may sit around in your stomach a bit longer, so you might wish to combine this with a fast absorbing source as well. When it comes to deciding on what source you will use, I tend to err away from drinks because its harder to keep track of how much you are getting in. That is of course until I get on the run and then try and keep that coke away from me.

The Considerations for you

Train for it

When it comes to deciding on your fuelling strategy, there are a few things to consider. The first is, that 90 g of carbs per hour can be a lot and I’ve had a lot of athletes over the years tell me they struggle to eat that much or eat much in the mornings. Well the good thing is, that in this case, nutrition really is just another discipline. You can train your gut. Starting 5-10 weeks out from the event longer if you are really worried, you should be working on increasing the amount of carbs you get in each hour on your big training days to try and mimic race day. You want to have at least 2-3 of those big brick sessions where you are fuelling exactly like you would on race day. Gradually build up to it. It may feel like a lot to start because your body isn’t used to it, but the more you expose your intestines to high concentrations of carbs the more they realise they need to respond and they will increase the number of those transport proteins in the intestine cells so that you start absorbing the carbs quicker. Note if you are training your gut to absorb carbs quicker, you can not be following a low carb diet the rest of the week as that will counteract the good work you did on that one training day. You don’t have to have super high carbs every day but you need to have carbs in your diet every day so your body knows that it needs to adapt to absorb carbs.

Flavour fatigue

The next thing to consider is flavours and carb fatigue. There are so many flavours I just can not stand any more because I have consumed too much of it in a race for example. So make sure you mix up your flavour combos during the training stage and don’t just rely on your favourite, because you don’t want to hate your favourite flavour come race day. I find that slightly saltier flavours are easier for me to tolerate like the margarita clif bloks and I actually just use a little bit of salt in my water bottle, and then plain water after that as hydration, so I can wash my mouth out after taking the sugar on board because I just hate that sticky sweet feeling and taste in my mouth. When it comes to Ironman, trying not to annoy yourself with little things is really, really important.

How much and when

Finally we need to consider volume and frequency. Jeukendrup again has done the research where they looked at which was better, small sips or large volumes so they got runners to consume either 50 ml every 5 mins or 200 ml every 20 mins and the findings show that the larger volumes resulted in 38% greater oxidation rates. This is because the volume in your stomach is also important for how quickly it gets tipped into your intestines for absorption. This is obviously easier to achieve on the bike than the run but can be done on the run if you slow down a little to get the fluid in. If you are using gels or bloks as your fuelling source this means following the instructions on the packet and actually following it up with a 200 ml chaser, but if you are relying on a liquid fuel like Tailwind for example then you need to take into account the volume you are consuming and either have small sips of concentrated fuel followed by water or take on much larger volumes than you may be used to but at possibly larger intervals. And that goes for coke as well, I always water this down on the run with one cup coke, 1 cup water.

Hydration

Which brings me to hydration. Most gels, bloks and sports drinks have electrolytes added to them so unless it is extremely humid conditions you probably don’t need to be taking on electrolytes as well. You also shouldn’t be following gels with electrolyte drinks anyway for more details on this I have written some detailed blogs on the science of hydration on my own blog. But the salt in hydration drinks do make them easier to consume and the research suggests that it is the dehydration that we should be worried about rather than loss of electrolytes because our body is pretty damn good at regulating these. My recommendations to my athletes is one bottle of water to every one bottle of hydration solution this way you can use the water to wash down your gels or other fuel source you are using and then the hydration solution can be used at any other point when you are thirsty. For hydration the recommendations are drink to thirst.

Tapering and race day

I have also written about the nutrition during taper on my blog but in general we want to keep it simple and keep it as similar and easy on your body as possible. Its all about stress reduction at this point. In the 2-3 days leading up to your race, you can consider having slightly higher GI carbohydrates and having a slightly higher proportion of your meals as carbs than fats and proteins. You don’t need to eat more or significantly change your diet, just a slight emphasis on carbs in the few days leading into the event. Because the training has reduced this increase in carb emphasis allows your body to naturally top the glycogen stores in your muscles and liver up so that you enter the race with maximal supplies. With such a small store already we don’t want to go in with them half depleted already.

Come race day, breakfast shouldn’t be anything fancy. Again focus on easy to digest and absorb, high GI carbs as the foundation of your breakfast and like with your in race fueling strategy, practice this as many times as you can in those big training days. Have a bit of protein and fats with this; bagel with peanut butter for example, cereal and yoghurt, cold potato and poached eggs – find what works for you. Have breakfast about 2 hours out so that its digested and in the process of absorbing and start hydrating now.

Final point to consider is whether to have something like a gel before the race. There is some research that suggests that triathletes in particular are susceptible to hypoglycemia in the first hour of exercise when they consume carbs in the hour before starting exercise, which has been related to the insulin response and the reduced access to fat and glycogen as fuel as a result. Most people will not have an issue with it and won’t even notice it but its worth trying out your pre-race nutrition in a race prior to your big one. If you do get symptoms of hypoglycemia, feeling shaky or nauseous for example then the best way to avoid this is to consume the carbs during your warm up or less than 15 mins before the race starts.

References and further reading