A 5-min guide to race day nutrition


In the « How To ? » section, we take the best of sport science and translate it into practical nutrition for endurance athletes.

Most of the time, nutrition is a very qualitative science : we are asked to eat a “healthy” diet, with “a bit of everything”. But when there is sports involved, quantification becomes necessary. Today, we will tackle the specific and crucial issue of nutrition during a race in a quantitative way. For the sake of time, we will limit the discussion to intense endurance exercise for up to, let’s say, the ironman distance.

There is a lot of old and new evidence indicating that nutrition during an intense endurance event is all about carbohydrates. When the duration increases and the intensity decreases, it’s a totally different topic. So, a much-needed discussion about ultra-endurance will come later (I swear)!

With that in mind, let’s do the maths and find out how much carbs are needed on race day! Let’s break things down by event duration.


a. Very short events (< 20 to 30 min):


Forget race nutrition strategy and run as fast as you can!

b. Short events (30 min to 1 h):

Rinse your mouth with (or drink) a carbohydrate-containing solution (no need to go higher than 30 g of carbs/h)

For a long time, we thought there would be no advantage of eating carbs in short duration events. If we have enough glycogen in our muscles to fuel such events, why would we need more exogenous carbohydrates?! But interestingly, studies have shown that if you rinse your mouth with a carbohydrate solution during short duration events (yes, just rinsing, drinking is not necessary), you will run faster. It is still unclear exactly why it’s the case. The current theory is that the brain normally prevents us to achieve our highest performance, probably to keep us from damaging our tissues and from in fine killing ourselves. A carbohydrate-sensing mechanism on the tongue may inform the brain that more energy is coming, and the brain may then allow us to unlock some more of our athletic potential.

A photo by Aidan Meyer. unsplash.com/photos/nvj-PDU98WU

Yes, you can also pour your sports drink all over your face and see if it sill works.

c. From 1 to 2 h:

30 to 60 g of carbs/h

Here, we are in the sports nutrition science “sweet spot”, where a lot of different types of sports drinks have been tested in interaction with different exercise modalities. Go ahead, it does improve performance compared to water alone.

d. Above 2 h:

up to 60g of carbs/h

90 g/h with a mix of glucose and fructose sources may be an option

Studies using carbohydrate sources providing glucose only (such as dextrose or maltodextrin) suggested that, above 60 grams of glucose per hour, the extra glucose ingested was not used to provide extra energy to the muscles. It was consequently considered as useless to drink more carbohydrates than this 60 g/h limit. The current hypothesis (lacking mechanistic support I have to say) is that the gut transporter that allows glucose to enter our body gets saturated. Knowing that fructose enters our body through another door than glucose, it has been suggested that we may overcome the 60 g/h barrier by adding a bit of fructose to the traditional glucose drinks. There is quite some literature around this idea, sometimes conflicting literature, but the bottom line is that it seems possible to increase the contribution of exogenous carbs (those we eat) to the energy supply to the muscles using this technique. Practically, this is done by drinking up to 90 g/h of a mix containing 2 glucose for 1 fructose (NB: saccharose contains one glucose for one fructose, some packages may even indicate the glucose:fructose ratio).



The frequency at which you drink or eat during a race is a key factor for a successful nutrition strategy. Two physiological processes play a role in this issue: 1/ the rate at which your stomach transfers food or fluids to your intestine (this is called “gastric emptying”) and 2/ the speed at which your intestine can take up the carbohydrates. During intense exercise, these 2 processes are particularly disturbed, because the increased blood perfusion in the muscles make the stomach and the intestine less likely to function properly.

To make a long story short, the key message is:

Eat or drink often (15-20 min), have small bites or sips

Studies have shown the superiority of this approach compared to ingesting larger amount of nutrients at bigger intervals. Thus, the “small and often” approaches reduces the likelihood of gastrointestinal distress, one of the biggest enemies of performance! Practically, I found it helpful to set a 20-min “nutrition” timer on my watch.

3. IN WHICH FORM (gel / drink / solid / …) ?



Some studies indicate that, at high intensity, solid food (ie bars, or real food items) may lead to more gut discomfort than a gel (with sufficient water) or a drink. For very intense events, this may even lead to a reduction in power output, probably by decreasing comfort and ease of exertion.

But, as often, this is clearly an issue of individual tolerance. So, here, the rule is:

Do whatever pleases your gut.

Test all your food during training sessions (at race pace) or B-races.

Of course, gels / drinks / bars bring a slightly different amount of carbs. You can keep in mind that:

  • a gel gives about 15 to 25 grams of carbs.
  • a drink usually contains 30 to 40 grams of carbs for each 500 mL.
  • a bar has around 20 to 40 grams of carbs (but very likely also other macronutrients)




Adaptations to extreme environmental conditions (heat, cold, altitude, …) are best achieved with acclimatization strategies. Nevertheless, little adaptations of the nutrition strategy on race day can help. When carbohydrates are provided with sports drinks, it is recommended to:

dilute or concentrate your sports drink based on your hydration needs

In other words, dilute your sports drink when it’s hot (because you will most likely drink a lot of it) or concentrate it more in a cold environment. A practical advice would be to use a powdered form of a sports drink and adjust the concentration yourself. Quantitatively, we can estimate that most sports drinks contain 60 to 70 grams of carbs / liter. So, dilute up to 30 g/L for ambient temperatures > 20°C and concentrate up to 80 to 90 g/L for cold races (< 10°C).


Nutrition, like any other elements of a race strategy, does not always go according to the plan. So, think of a plan B! Say, if you already feel gastrointestinal discomfort after 15 km in a marathon, be mentally prepared to switch to an alternative plan. For example, you may consider one of the following options (in this order):

  • Reduce the workload for your gut. Stop solid food and choose gels + water or sports drink.
  • Reduce the concentrations of your sports drink, maybe by grabbing both water and sports drink at the next aid station and mixing them.
  • Give your gut a brief rest. Increase the gap between your nutrition moments to 30-40 minutes (instead of 15-20 min).


1/ try and plan everything before race day

2/ the longer the race the more carbs per hour (with the upper limit of 90 g / h)

3/ the more intense the race the more it is difficult for you gut, so go for fluids.

4/ modify your nutrition plan based on the race conditions and be ready to move to plan B!

To conclude, it is important to highlight that we only talked here about race day nutrition. There are now fascinating new developments concerning optimal nutrition to trigger training adaptations. These new diets notably experiment with very low carbohydrate intake, which is clearly in contrast with the high carbohydrate intake needed on race day. More on that paradox in a future article!



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