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Nutrition for Endurance Athletes: Everything You Need to Know

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Nutrition for endurance athletes is a broad topic. A lot of similar principles apply between most endurance events, although there will obviously be differences.

In this article though, the goal is to cover as much as possible, while also addressing a lot of aspects of nutrition and how it can improve performance.

Intra-Race Carbs

intra race carbs gels

Glucose is our body’s most efficient fuel source for exercise above a certain intensity.

Later I will discuss low carbohydrate approaches. But for now, we will leave that aspect and just focus on the carbohydrate portion of the discussion.

Glycogen is the body’s stored form of glucose/carbohydrate. 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 if you nail your carb loading strategy, it is unlikely that you will be able to have >90 minutes’ worth of glycogen stored when exercising at the intensity a marathon requires.

It seems that the hourly limit for glucose absorption is around 60g per hour.

Theoretically, if you are consuming glucose as your sole carbohydrate source, it likely would not be beneficial to go above that point. Going too high also increases the risk of gastrointestinal distress reducing race performance.

When multiple carbohydrates are used though, the number gets higher.

A 2:1 ratio of glucose/maltodextrin and fructose appears to raise that theoretical number to about 90g per hour. Even just this small piece of information can give you an edge over your competitors if they are not implementing this.

Cyclist eating a sports gel

This has been well studied with a lot of conclusions coming back with the 90g per hour or even slightly lower being optimal for performance.

Even though this is the theoretical number, 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 a specific 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.

Nailing intra-race carbohydrates can make a huge difference in performance. It takes time to build up to whatever level is optimal for you, but it can give you a significant boost in the times you are able to achieve.

Carbohydrate Loading

Carbohydrate Loading

Carbohydrate loading is a nutrition technique that you can use to prolong optimal performance and delay the performance loss associated with depleted glycogen.

Carb-loading if done properly, essentially allows you to store near the maximum possible amount of glycogen.

From this stored form, the body can transform glycogen back into glucose through a process known as glycolysis and provide energy when needed.

This means you start the event in the best position possible.

It used to be believed that you had to first deplete your muscles of glycogen to take advantage of their compensatory carbohydrate loading effects. Recent research has shown that this step is not necessary.

Current best practices for carbohydrate load can be simplified to:

Increase carbohydrate intake to 10–12 grams of carbohydrate per kg of body mass per day, for 36–48 hr leading up to the event. This will saturate your muscles with a maximal amount of glycogen. 

Reduce training in days leading up to the event to ensure muscle glycogen is not being depleted, and complete rest is often advised the day before the competition. 

Carb Loading Example

If you struggle to get to the 10-12g/kg mark, then going slightly lower will still be effective, even if it is slightly sub-optimal.

It is worth noting that when people typically carb load without a strategy, they will often end up only consuming 5-6g/kg/day. Therefore, planning out how to achieve this high amount of carbohydrates can really help achieve the outcome you want.

Carb loading food list

Caffeine

As a general guide, doses of 1-3mg per kilogram of body weight of caffeine have been shown to elicit performance enhancements for events lasting at least 30mins.

Cup of coffee and coffee beans on wooden table

This might take some trial and error though. Some athletes might prefer to stay away from the higher amount. Others will prefer the lower end of the spectrum.

Caffeine typically reaches peak blood concentration at around the one-hour mark and remains steady for around 3-4 hours. So, it would make sense for an athlete to consume caffeine around an hour before their event or training session.

And for longer endurance events it can make sense to have more caffeine throughout the event as well. A standard guideline is 3-6mg/kg in total, including during the race. Obviously, there can be exceptions for ultra-endurance events though.

Personally, I do not recommend trying to reach this target through coffee. A study done at Griffith University looking at single shot espressos from a range of outlets across the Gold Coast showed that caffeine content varied from anywhere between 25-214mg!

Coffee CAN work well. But because the dosage of caffeine is inconsistent, it makes sense to use a source of caffeine where you know the exact amount.

The topic of caffeine tolerance is complex though. At this stage, the research seems mixed. But the current consensus seems to be that:

  1. High habitual intake of caffeine does seem to reduce the benefit of caffeine when consumed for performance purposes.
  2. Consuming a slightly higher amount of caffeine than usual intake can potentially offset this issue.
  3. If habitual intake is very high, it probably does not make sense to go higher than that level.
  4. The concept of withdrawing caffeine leading up to competition and then reintroducing it has theoretical merit, but the research that is available at this stage has not shown it to provide any noticeable benefit.
  5. Ideally, regular caffeine intake should be <3g/kg/day, which seems to mitigate these issues come competition day.

Electrolytes

Electrolytes are surprisingly low on the list of priorities for endurance athletes.

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.

As an extreme example, if you happened to undertake an event with an exceptionally long duration, while only drinking water without electrolytes, you could potentially be at risk of hyponatremia.

This does not happen for shorter events, because they tend to be finished before this risk arises.  

Sodium is the main electrolyte one people need to be concerned about. The guideline for sodium is to consume 300-600mg per hour during an event.

Beyond that, if you use most commercial sports drinks/gels, electrolyte intake typically sorts itself out without you needing to think about it.

Beetroot Juice

Beetroot Juice for Endurance Athletes

Beetroot juice is an easy option that can be used to improve endurance.

The way it works is through the effects of nitrates.

Nitrates are typically found in vegetables and they mainly act by vasodilation and improved blood flow.

And beetroot is particularly high in nitrates.

The current consensus is that beetroot juice reduces the energy cost for movement, which improves efficiency and that there is enhanced muscle metabolic function, which also leads to less muscular fatigue during exercise.

One notable study highlighted that runners who consumed a shot of beetroot juice pre-race cut 1.5% off their 5km time.

Although time-to-exhaustions (TTE) trials can have the major flaw that they are not exactly relevant to actual endurance sports like running, cycling or swimming, another study on cycling showed a 16% improvement in TTE.

And lastly, since single studies can paint a misleading picture, there is a meta-analysis of 23 beetroot juice studies highlighting that beetroot juice consistently improves performance in endurance events.

The ideal dosage appears to be around 5-7mmol of nitrate for most people, taken around 3hrs before training. This equates to roughly 250-300g of nitrate-rich vegetables per day.

Beet-It Supplement

This equates to 500ml of regular beetroot juice or 70ml of Beet It, which is a more concentrated version.

It is also worth noting that taking beetroot juice daily for 3-4 days improves effectiveness even more than acute dosage. Arguably it would make sense to do that instead of just a once-off dose. The effects seem to plateau after about 6 days though.

The final thing to be aware of is that you cannot brush your teeth or use mouthwash right after taking beetroot juice. This can block the conversion of nitrates into nitrites, which also blocks the effectiveness of the supplement.

Body Composition

Having reduced body fat while maintaining muscle mass can obviously improve power to weight ratio. And this typically will carryover into improved performance.

In some cases, increasing muscle mass can improve performance or reduce injury risk too.

There is arguably a point where excess muscle mass hurts performance in some events too.

The main way for people to improve performance through improving their body composition though is improved power to weight ratio.

For those looking to get leaner, my best advice is to read this blog post.

It can make a night and day difference to performance and honestly is probably one of the biggest factors, which is why I think having a blog post for it by itself will do it more justice than writing about it here.

At another end of the spectrum, it probably does not make sense to be exceptionally lean year-round. There can be detrimental impacts from being excessively lean at all times. This is part of why, for top-level athletes, it can make sense to periodise body composition, like is done in this case study.

Low Carb Approaches

Dietary Fat

One thing I want to address before any other factors associated with a low carb diet: If the diet improves your body composition, that could be what leads to the performance improvement, not the specific diet.

Keep that in mind for all dietary approaches. There are people who will get benefits from vegan diets, keto, carnivore, and an endless list of approaches. And a large portion of this comes from body composition changes.

Typically, reducing carbohydrate intake will also reduce calorie intake. This will typically lead to fat loss.

Instead, I will be looking at this from the perspective of what would happen assuming you were already at optimal body composition for endurance.

One of the main theories behind the potential benefits of a low carb diet is that it allows and endurance athletes to utilise fat to a greater degree while exercising. And since the body has a much larger energy reserve from fat (even in lean individuals) this obviously could be advantageous over glycogen and glucose.

While this sounds great, this has been shown to reduce exercise economy and increase the oxygen requirement to produce each unit of ATP.

One of the most publicised studies in this area is by Louise Burke and it demonstrated that even for race walkers (who theoretically would benefit more than most endurance athletes from a low carb diet), a ketogenic diet appeared to be inferior to a higher carb diet over a 3 week period.

Ketogenic Diet Meal

In this study, the ketogenic group also had a significantly increased rate of perceived exertion as well. Basically, the training felt harder for this group.

The main criticism of this study was that it was not long enough. People argued that fat adaption takes longer. And although Louise Burke highlighted clear evidence that 3 weeks is long enough for the benefits of fat adaption to be observed, this is arguably still a valid criticism.

There was also an argument that people could reap the benefits of low carb in training, reintroduce carbs pre-competition and get the best of both worlds.

Unfortunately, these benefits were still not observed when the methodology was repeated, except with two weeks of high carbs leading into race conditions was tested.

And the overall body of evidence at this stage seems to line up with this thinking.

Train High, Sleep Low

One of the theoretical reasons why going low-carb in training and then going high carb leading into a race might not be effective, is because it takes a while for the body to optimise the ability to absorb/utilise carbohydrates.

It takes time to “train the gut” to tolerate large amounts of carbohydrates while exercising as well.

Based on this, one theoretical model could be to periodise carbohydrate intake across the week.

It could make sense to have some training sessions in a high-carb state and some sessions in a low-carb state.

There are reasons people do low-carb approaches. There are theoretical benefits, such as improving the body’s ability to use fat as a fuel source.

Training in a low-carb state allows you to reap some of these benefits. Training in a high-carb state allows you to improve your ability to utilise carbohydrates.

This could look like:

Eating carbs throughout the day and training in a high carb state in the afternoon. Followed by having minimal carbs until after the next training session. And just cycling those approaches.

And to optimise it further, ideally, you could have more carbs leading into and during important sessions and be low carb for less important sessions.

This is a theoretical approach that is being observed, but there is not much formal research at this stage to support its efficacy for actually improving race times yet.

Hydration

Endurance runner drinking from a bottle

The easiest piece of advice for hydration is “drink based on thirst.”

That advice is preferred over a lot of other advice. Partly because it is simple.

And what happens if you sweat more than the average person? What if it is a hot day? What if it is a cold day?

For sure you can do sweat testing as well as do a lot of trial and error.

But I see drink based on thirst being a starting principle, and then you adjust from there as needed.

Dehydration clearly is detrimental to performance. And a typical rule is that if your body weight drops by more than 2-3%, dehydration is likely going to be impacting performance negatively.

Alternatively, drinking too much fluid has to obvious downside of adding additional weight with no benefit, as well as potentially influencing risk of hyponatremia. Plus, the physical act of drinking slows you down a little bit.

In practice, it is likely best to do a combination of drinking based on thirst, while also trying to find that point that leads to you losing no more than 2-3% of body weight.

Putting It All Together into an Effective Overall Strategy

Some main priorities to take away from this are to:

  1. Optimise your body composition through nutrition.
  2. Optimise your carbohydrate intake through carb loading and intra-race carbohydrates.
  3. Utilise caffeine in a way that improves performance.
  4. Consider concentrated beetroot juice supplementation for improved performance.
  5. Do no harm when it comes to electrolytes. Basically, avoid any detriments to performance.
  6. Maintain adequate hydration. Try to avoid losing >2% of body weight, but also avoid overhydration.

Implementing these steps can dramatically improve your performance. Not many athletes are nailing all of these aspects. So even though a lot of this seems simple, implementing it can go a long way towards helping you achieve your goals.

By Aidan Muir

Aidan is a Brisbane based dietitian who prides himself on staying up-to-date with evidence-based approaches to dietetic intervention. He has long been fascinated by all things nutrition, particularly the effects of different dietary approaches on body composition and sports performance. Due to this passion, he has built up an extensive knowledge base and experience in multiple areas of nutrition and is able to help clients with a variety of conditions. One of Aidan’s main strengths is his ability to adapt plans based on the client's desires. By having such a thorough understanding of optimal nutrition for different situations he is able to develop detailed meal plans and guidance for clients that can contribute to improving the clients overall quality of life and performance. He offers services both in-person and online.