Drinking; Eating


When you run and get hot, your body uses three ways to cool down. Sweating, increased blood flow to skin (redness) and slowing down. When you sweat,  you lose water. The amount of sweat varies a lot between individuals. Sweating means the body loses water, but also electrolytes such as sodium, potassium and magnesium.  

Becoming dehydrated increases the workrate of your cardiovascular system, causes greater perceived exertion and alters your metabolic functions. You will feel tired,  so it is to be avoided! So the reason we need to consider hydration is because of its potential affect on our performance.

Before a Run

It is possible to drink too many fluids before a run. However it is unlikely you will reach that point. Your best guides are your thirst (though nerves can bring on a feeling of thirst) and colour of urine (straw or light yellow) as these are pretty good indicators of your hydration level before a run. If you do drink a lot of water too quickly before an event, it can produce clear urine (“going straight through you”) because your body has had insufficient time to absorb it so you actually end up a little dehydrated. Have your drinks  in small amounts over at least a few hours.

Sports drinks can be a help, though they are not essential, as they contain some of the electroytes you lose when you sweat. These electrolytes are also found in bananas, beans, greens, fish and many other foods. Salt is common in our diets. 

Energy drinks like Red Bull are not appropriate. 

During a Run

The only reason to take in fluid is to avoid any reduction in your performance caused by dehydration. If your performance is not affected then don’t drink during a run. Sir Mo would not be seen in the 5k or 10k races stopping for a quick drink!  Many club runners do not drink during a 10k race, excepting to freshen their dry mouths and throats.

Half marathons and longer distances are a different matter, as glycogen stores will become reduced in the second half and taking on extra carbohydrates is usually necessary. These can be in the form of a sports drink or energy gels. If energy gels are used then you should also have a small cup of liquid to help them get down to the stomach.

The longer the race, the higher the temperature, the more important it is to replace electrolytes. These are almost always found in sports drinks and energy gels.

Also, there is no value in drinking more quickly than your stomach can take in and distribute the liquid, otherwise it just sloshes around ineffectively. Research has shown that a maximum of about 200ml of fluid can be dealt with effectively by your stomach in fifteen minutes or 800ml in an hour, while running. If it takes 15 minutes for a drink to travel from your mouth, through your stomach and into your blood system, then you might consider it is not helpful to slow down for a drink in the last 15 minutes of a race.

After a Run

You are aiming to give your body the best chance of a fast and full recovery. You want to refill your glycogen stores in your muscles and liver together with re-hydrating. See below for Nutrition.

Your fluid intake should be at least the same as the amount sweated. You can use thirst as a measure of how much is needed, but most runners do not drink enough. It might need a couple of days to recover to normal hydration levels.  Adding a pinch of salt to drinks can help retention. Of course not everything you drink stays in your body as your stomach can only deal with so much liquid per hour. You may well need to drink 150% of the amount you have sweated in order to recover. Don’t worry too much about replacing eletrolytes, as your meals will will contain these.


When endurance running, your body burns carbohydrate and fat to create energy. The carbohydrate that is burned has been stored as glycogen in the muscles and liver. Our bodies can only store a limited amount of glycogen, compared to a very much greater ability to store fat. But to turn fat into energy needs a lot more oxygen than the oxygen needed to turn glycogen (carbohydrate)  into energy, so we cannot maintain as fast a pace burning fat as we can by burning glycogen (carbohydrate). We get out of breath more easily as glycogen stores decrease and we depend more on fat as the energy source.  

So one of our objectives as endurance runners is to be able to store as much glycogen as we can so it lasts as long as possible, as it is a more efficient energy source than fat.

But we will need to use our fat stores, we can’t just rely on glycogen, so the second objective is to train our body to make the most use of the increased oxygen requirement needed to convert fat to energy.  This will happen if we develop our aerobic fitness. It is not a quick fix as aerobic development never is. Aerobic fitness can be built through long slow runs, repeated over long periods of time.

This helps us to understand why it is sometimes appropriate for a runner in a long race (over 90 minutes) to think about ‘carb loading’ in the days leading up to the race, in order to stock up on the reserves of glycogen in the muscles and liver. But for almost all endurance runners (elite aside) a normal healthy diet is adequate and carb loading is quite uneccessary. Allow about 3 or 4 hours after a meal before running. If you are running in the early morning, you will not have time to eat beforehand, which is perfectly okay if you build up your morning running volume over time and not suddenly start running long distances on an empty stomach. 

If you find there could be about six hours between a normal meal and a run, have a small snack, a banana for example, about an hour before running.

After running, your primary objective should be to replace the glycogen in your muscles and liver. There are many sources that you can Google that will guide you as to what food is best. Battered fish and chips are not high on the list!

If you have done a run that has been moderately tough or harder, you should eat within 30 to 40 minutes of finishing to stand the best chance of refilling your glycogen stores. Leave it longer and the body is less good at converting your food into glycogen.  The rate of potential replenishment of glycogen storage is at its highest immediately after running, diminishing over about six hours. The first half hour is the very most effective, then the next hour less so, then the next and so on. Eating some carbohydrate (not a lot) with a high glycemic index within 30 minutes of the end of your run together with a little protein, then more within the next hour will help to stimulate gycogen storage. Bread, bagels, crackers, rice cakes, jelly beans are examples of high GI foods.  Then have a larger meal as soon as you can.

Graeme Loudain – September 2019

These notes are published as a general aid to all endurance runners. They are guidelines based on current best practice, intended to illustrate the points in the articles rather than provide a precise training schedule. They are written in a way to be of help to runners. Individuals will have their own requirements and the content of the notes will not suit all. Please use them in the spirit in which they are intended and modify them to suit your own needs. If you have suggestions for improvement, amendments or comment, please email gladmin@btinternet.com.