What to eat before a run - a guide for athletes

Posted by Stephen Tannatt Nash on Apr 27, 2017 7:59:13 PM
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In order to answer the question as to what to eat before a run, you have, perhaps accidentally, realised that the food you eat determines your performance on your runs. This epiphany that food isn’t an object of entertainment, but is as important as the high octane fuel you would put in an F1 car, is about to take your running to the next level!

A simple google search of “what to eat before a run” will show you a long list of articles that are written in a way to attract views and reads without providing any real value or building any real trust in what they say. Hopefully this one, and a small selection of the articles written by other Sports & Exercise scientists, Sports Nutritionists or high level coaches, will provide you with a more trustworthy source from which to base your pre-race knowledge on.


Determinants of Performance for Running


You have probably covered the energy systems to death but I will reiterate this for you in simple terms so that you can understand not only know the recommendations of the evidence we provide in this article but why those recommendations make sense. As always the advice offered in this article is subject to you utilising it in a voluntary capacity and equally subject to you not having any conditions, medical or otherwise, that mean you should not follow this evidence based advice.

In looking at “running” I simply mean the runs of 5km plus or the runs of over 15minutes right up to and including Ironmans. These runs are largely contributed to, and performance limited by, the aerobic energy system (Baechle & Earle, 2008). The limiting factor here is the rate at which the energy required for your intensity of running can be sustained.


EXAMPLE: If I was to run and require 100 units of energy to run at 15mph for 10 minutes, but my stores only held 600 units of energy, then I could run at 15mph for 60 minutes. In order to go 20mph let's say I need 133 units of energy I would only be able to keep that up for 45 minutes. Once I have run out of energy I would have to switch to a backup energy source that wouldn't be able to provide the energy quick enough and I would therefore go slower.

Two ways we can fix this situation to allow us to either keep a higher rate of speed, or a slower rate for longer, is to either increase the capacity to store energy (hence where training comes in) or to find a way to make energy available to replenish the stores whilst you’re still running (Supplementation).

Please bare in mind this is meant so that people can wrap their head around this subject and not meant to be a holistic appraisal of how the energy systems work in the depth and breadth of the specialism!


The way in which you are looking to improve this factor is by utilising nutrition to supplement the amount of energy able to be provided over the course of your race and by making sure your reserves are topped up prior to your run.

Whilst there are a myriad of determinants for running performance, nutritionally one of the main focuses is the supplementation, or intake, of carbohydrates to provide the energy required to run for distance. When training we see adaptations to levels of glycogen storage, meaning that the total amount of glycogen that we can use before it runs out is improved (Baechle & Earle, 2008). Equally, we see our efficiency for using that energy improving, causing us to get a better bang for our buck from the energy we do use. We often call this Running Economy.

Another place we can get glycogen from that allows us to run further for longer is our liver. When our muscle glycogen levels drop low enough the liver starts to utilise a process called fructolysis to turn fructose into glycogen. It then shunts this new glycogen into the bloodstream to be utilised as a fuel source by whatever muscular tissues are demanding additional glycogen resources. Once this runs out we fall back on fat oxidation which is a much slower energy source and our ability to maintain speed diminishes.


Firstly, let’s just iterate why blood is important. 40%-65% of your body weight is water (Von Duvillard et al., 2004)! 5litres of this is in the blood with 40% of the water being held in the cells. The blood is made up of two component parts Blood plasma and Blood cells. Any form of dehydration will cause the fluidity of these structures to be reduced leading to increased viscosity. When blood becomes too viscous it clots (say no more!). Prior to it clotting it becomes increasingly difficult to transport glycogen and other organic compounds around your body required for you to perform.

Pre-Run Recommendations


So, we know that in order to keep our muscles going we need to have trained, to increase the storage capacity of glycogen in the muscles, but we also need to make sure those stores are topped up! On top of that it would be good if we could carry a little bit extra in our blood wouldn’t it? Also something to note is that more carbohydrate does not necessarily elicit better performance but helps maximise your current performance potential.

Making sure you have enough carbohydrate in your diet around the clock to top up your glycogen stores is imperative. In order to recover glycogen stores within a day of racing/training you are looking at 60% (Maughan, 2002) of your daily calorific intake coming from carbohydrates. Arguably, however, if you aren’t training everyday with long runs that can deplete your muscle glycogen, or hard interval training, then a standard carb intake, of 40% carbs for instance, would be suffice to replenish glycogen levels over a day or two.

Acutely prior to exercise, within 1-hour, there is plenty of people on both sides arguing whether to ingest food or not. Plenty of sources cite gastrointestinal distress as a reason why not to eat or drink prior to a run whilst others suggest that the hypoglycemic response elicited after ingesting high GI foods would result in performance decrements. However, evidence has shown that carbs within the 1-hour pre-run time increases, or rather maximises, athlete performance (Febbraio et al, 2000; Jeukendrup & killer, 2010) and that despite there being a link to hypo-type symptoms the blood sugars don’t seem to reach to hypoglycemic levels.

Possible mechanisms of action for this performance are that the carbohydrates sit in the stomach and are absorbed at an average of 1g/min while exercising meaning that there is a constant release of glucose being released into the blood plasma to be utilised as fuel by the muscles (Gonzalez et al, 2015). This has the benefit of sparing the muscle glycogen stored in the muscles themselves being used up first!


Luckily, the whole water issue is pretty straight forward. 2 hours Prior to the event/race/session you should consume around 500ml of fluid (Baechle & Earle, 2008). This will allow you to make sure you are hydrated optimally and get rid of any excess water (nobody likes to run on a full bladder!) before you go for a run!

Equally if you can work out your sweat rate prior to the event then you are going to be increasingly well prepared! To do this weigh yourself prior to a run then run at your race pace for an elected distance. Once finished weigh yourself again. The weight lost in grams is the amount of ml of water you need to consume over that time frame. More on this shortly!

Intra-Run Recommendations

Unfortunately, due to the added difficulty of carrying and delivering carbohydrates whilst running a lot of the research has been done in cycling. Luckily there is a proven crossover between the results found in cycling to running (Jeukendrup, 2011).


As mentioned previously we know there are two sources of glycogen in our body. Firstly, muscle glycogen and, secondly, our live glycogen. In sub 40 minute races it is unlikely that you will need to top up, or even be able to due to pace, your glycogen stores. However, in longer races/training sessions it is imperative you do. In order to top up your muscle glycogen the easiest route is by ingesting glucose and In order to top up your liver glycogen we need to ingest fructose (Jeukendrup, 2011). The maximum rate we can ingest glucose is about 1g/min but if we ingest fructose alongside the glucose then we can ingest at rates of around 1.5g/min (Burke et al, 2011).

This basically means that over the course of an hour 90g of carbohydrates, in the form of glucose and fructose can be absorbed providing a continual drip feeding of glucose to the system.

The oxidation rate of these carbohydrates appears to be around 1.75g/minute (Burke et al., 2011; Jeukendrup, 2011; Jeukendrup & Killer, 2010; Jeukendrup, 2010) meaning that even at peak ingestion rates you are always going to be in a deficit (providing you are running hard enough to warrant this rate of oxidation!).

One thing we need to bare in mind is that most of this research was done with cyclists who had water available on demand in a lab. This meant they could concoct a solution of 20mg sodium, 90g of carbohydrate (glucose:fructose 2:1) and 500ml of water per hour.

In reality, you are going to struggle achieving this and will have to resort to gels, most of which are maltodextrin and come in 20g bursts. Some do come with electrolytes and will help you to maintain hydration throughout the race. Luckily Jeukendrup (2011) have provided this handy table for you.

Screen Shot 2017-04-27 at 19.37.12.png

Fig. 1: Recommendations for Carbohydrate intake during different length endurance events (Jeukendrup, 2011).


Let’s go back to sweat rate. We know that, for example, if you lose grams after a 30 minute run, you know you need to drink ml afterwards to replenish. On top of that we need to make sure that we get some sodium in there to keep the water gradient in our stomach the right way round. Otherwise despite being dehydrated our body will have lost all its salt through sweat and won’t be able to absorb any of the water we have swallowed in.

However, extrapolating that we know we would need 2ml an hour to stay hydrated! Whilst running for longer distances we therefore know we need to top up our water as we go somehow! How you deliver that depends entirely on the race you are in and the equipment you have/want available.

If you are running in races where there are water stops then you are more or less going to have to just get through it and estimate how much you should be drinking at each stop. However, in longer races where camelbacks, for example, are permitted you could always utilise the reservoir to put in sucrose and sodium too.

To download this guide as a pdf, fill out the contact form below and it will be emailed to you!



Baechle, T. R., & Earle, R. W. (2008). National Strength & Conditioning Association (US). Essentials of strength training and conditioning. Champaign, IL: Human Kinetics, 395-396.

Burke, L. M., Hawley, J. A., Wong, S. H., & Jeukendrup, A. E. (2011). Carbohydrates for training and competition. Journal of sports sciences. 29(sup1), S17-S27.

Febbraio, M. A., Chiu, A., Angus, D. J., Arkinstall, M. J., & Hawley, J. A. (2000). Effects of carbohydrate ingestion before and during exercise on glucose kinetics and performance. Journal of Applied Physiology. 89(6), 2220-2226.

Gonzalez, J. T., Fuchs, C. J., Smith, F. E., Thelwall, P. E., Taylor, R., Stevenson, E. J., ... & van Loon, L. J. (2015). Ingestion of glucose or sucrose prevents liver but not muscle glycogen depletion during prolonged endurance-type exercise in trained cyclists. American Journal of Physiology-Endocrinology and Metabolism. 309(12), E1032-E1039.

Jeukendrup, A. E. (2010). Carbohydrate and exercise performance: the role of multiple transportable carbohydrates. Current Opinion in Clinical Nutrition & Metabolic Care. 13(4), 452-457.

Jeukendrup, A. E. (2011). Nutrition for endurance sports: marathon, triathlon, and road cycling. Journal of sports sciences. 29(sup1), S91-S99.

Jeukendrup, A. E., & Killer, S. C. (2010). The myths surrounding pre-exercise carbohydrate feeding. Annals of Nutrition and Metabolism. 57(Suppl. 2), 18-25.

Maughan, R. (2002). The athlete’s diet: nutritional goals and dietary strategies. Proceedings of the nutrition Society. 61(01), 87-96.

Von Duvillard, S. P., Braun, W. A., Markofski, M., Beneke, R., & Leithäuser, R. (2004). Fluids and hydration in prolonged endurance performance. Nutrition. 20(7), 651-656.



Topics: running,, sports performance, sports nutrition, cycling

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