Intra-race nutrition for marathon runners, or really any endurance sport that involves a longer duration, can make a huge difference. It is one of the easiest things that can be implemented to improve race times.
It is also an area I do not see many people implementing nearly as well as they could. If you care about competition, this can give you an edge. If the only competition you care about is improving your own race times, then this will still obviously help you do exactly that too.
Glucose is our body’s most efficient fuel source for exercise above a certain intensity.
While there is debate over low-carb vs high carb approaches, the above statement is not one that should be controversial.
Although we have larger amounts of energy available via fat stores, carbohydrates allow you to run at a higher percentage of your maximum potential output.
The faster you are moving, the faster you are burning through glucose. And this leads to quicker glycogen depletion since glycogen is the storage form of glucose.
As glycogen levels start getting closer to being fully depleted, performance starts to decline.
This phenomenon is something that you can see in race splits. This is a large portion of what people call “hitting the wall.”
Even with a perfect carb load, it is unlikely that you will be able to have >90 minutes’ worth of glycogen stored when exercising at the intensity a marathon requires.
Beyond that, this is even more important since there is likely a performance decline before full depletion anyway.
Based on this concept, it makes a lot of sense to have intra-race carbs. This introduces a steady stream of glucose into the blood, slowing down the depletion of glycogen.
Obviously, this should carry over to improved performance. This allows you to perform at a higher level for longer, which can lead to significantly improved race times.
How Much Carbohydrate Should You Consume Intra-Race?
Intra-race sports nutrition has been an interesting space to watch over time. And I think it is an area that still has a lot of potential room for improvement in the future.
Originally people were only drinking water while racing. This is obviously sub-optimal, given the knowledge we have from above.
Then people started noticing benefits from certain strategies.
One of the first documented popular strategies including the use of flat Coca-Cola, which has the benefits of both sugar and caffeine.
The first major breakthrough was discovering that the hourly limit for carbohydrate absorption appeared to be around 60g of glucose per hour.
This is roughly the amount of glucose that the body can tolerate and absorb, even from a theoretical perspective.
Going above that is likely adding no additional benefit. But going beyond that point likely starts to significantly increase gastrointestinal distress, which we obviously want to avoid.
The next major advancement was learning that if you use multiple carbohydrate sources it can raise that number even higher. So this would involve using something like fructose alongside glucose or maltodextrin.
A 2:1 ratio of glucose/maltodextrin to fructose seems to raise that theoretical number to about 90g per hour.
This has been well studied with a lot of conclusions coming back with the 90g per hour or even slightly lower being what is optimal for performance.
This 90g per hour number seems to be a common consensus amongst a lot of people in the evidence-based community. Heck this was also a number I was taught by elite practitioners in the sports nutrition space.
But it is worth noting that certain people at the elite level go even higher than this in practice.
Some Tour De France riders get as high as 107g/hr. And there is also research indicating that mountain runners continue to see performance benefits beyond the standard 90g per hour by going as high as 120g per hour.
This obviously makes me think that we should not limit ourselves to an arbitrary number. Instead, the goal should really be to see how high we can get our hourly carb intake intra-race before experiencing downsides like gastrointestinal distress.
Thoughts on Protein
I have seen a lot of arguments for including protein into intra-race nutrition, or at least intra-training nutrition. Some numbers chucked around are a 4:1 ratio of carbs to protein.
There is obviously the potential that having a steady stream of protein or amino acids coming in during a session might lead to a reduction in muscle breakdown. It could also theoretically improve recovery.
But if daily protein intake is optimised, this likely makes no difference. This likely includes consuming sufficient total protein, while also having protein either pre-workout or post-workout.
One of the biggest flaws to look out for in research on this is being aware of total calories.
What I mean by that is that one group might get 30g of carbs per hour and the other group might get 30g of carbs and 10g of protein, as an example.
Obviously in that example, the group with protein and carbs is getting more total calories. Since protein can be converted to glucose, they likely also have more glucose available to fuel performance.
So, this leaves two options:
- Consume slightly less than the optimal amount of carbohydrates and add a bit of protein.
- Consume the optimal amount of carbohydrates and add protein on top.
Option one makes sense to me if protein is improving body composition over time, which would improve power to weight ratio.
It would also make sense if protein outperformed carbohydrates from a performance perspective. This just does not seem to be the case though.
Option two would make sense to me if that did not lead to the problem of likely contributing to gastrointestinal distress, since it is just adding more food/calories on top of what was already optimal.
While there are theoretical reasons to add protein intra-race, I just do not think it is worthwhile. Looking at top athletes in the sport, it does not seem like many people are doing it either.
Thoughts on Caffeine
Caffeine is something that very clearly improves performance. Ideally, having ~3mg/kg of caffeine pre-race is a strategy that can help improve performance slightly.
It helps to reduce rate of perceived effort, which obviously could help you push harder over the course of a marathon. But there can also be potential benefits beyond that.
In addition to pre-race, for an event as long as a marathon, it can make sense to have caffeine during the race as well. Some gels contain caffeine, which could make this easy.
If consuming caffeine during the race, the total target for caffeine for the race (including pre-race) should be 3-6mg/kg.
Electrolytes are surprisingly low on the list of priorities when it comes to intra-race nutrition.
I have spent a lot of time in the field learning from other experts and doing as much learning as I can. Throughout that time, I have noticed a trend where not many people are talking about how electrolytes can improve performance.
And the reason for that is that it seems like more of a “do no harm” than a “nailing this will improve your race times” type of situation.
It is also quite hard to find specific guidelines for electrolytes.
At one extreme, if you happened to run quite a slow marathon time, while only drinking water without having any electrolytes, you could potentially be at risk of hyponatremia.
This does not happen to quicker competitors since they finish the race before this typically develops.
Sodium, potassium, magnesium and calcium are the four main electrolytes in the body.
Sodium is the biggest one people need to be concerned about. The guideline for sodium is to consume 300-600mg per hour during a marathon.
Beyond that, if you use most commercial sports drinks/gels, electrolyte intake likely sorts itself out without you needing to think about it.
How to Start Introducing Intra-Race Nutrition?
With every race nutrition strategy, it is important to try it out in training first. It is typically not a good idea to try something new on race day.
Since the key factor that improves performance is intra-race carbohydrates, that is what likely will require the most trial and error.
The typical range that I think is relevant for most people is 30-90g/hr for carbohydrates.
Outlier athletes and those who have specifically built up their ability to take on carbs during intense exercise are likely the only people who can handle the upper end of that range.
Based on that logic, it is probably also a good idea to start low and build up.
Rather than jumping to the top end of that 30-90g/hr range, it makes sense to start at the lower end. And then slowly building up until you find that sweet spot for improved performance with minimal risk of gastrointestinal distress.
It is also important to be aware that you can literally “train the gut” to handle more carbohydrates while exercising. This allows you to take on even more carbohydrates to further improve your performance.
The people at the top end of the sport likely were not able to initially tolerate the amounts of carbs that they currently take on during races. It takes time to build up that ability.
You want to introduce them into your training and slowly build up to a level that works best for you.