top of page

How to fuel for a marathon

Marathon runners are starting to pay more and more attention to their nutrition. No one ever questions the importance of training, yet the importance of nutrition has often been underappreciated. Or perhaps the topic of nutrition seems to pop up on the radar only close to the marathon.. and this is when many questions suddenly arise. In this nutrition guide we will explain how to best fuel for your marathon. What should you eat the day before, or the morning of the marathon, and what drinks, gels and solids you should take during the marathon, and how often. Keep reading if you want to know the answers.

What can go wrong nutritionally during a marathon?

A large percentage of marathon runners struggle to get their nutrition right, and many who do not have a great run, blame nutrition: they ran out of energy, became dehydrated or experienced stomach problems. They ingested too much, or ingested too little. They tried new products they had not used in training, and so on. There are many new advances, and new products, and it can be difficult separating the sense from the non-sense.

Here are the most common mistakes:

Not having a plan.

Just starting a marathon thinking: "oh I will drink when I get thirsty and I will grab something at feed stations if I need it". It is a gamble. Maybe it will work. If you have prepared for your race, invested so many hours training and you have planned all your training, why not plan your intake, and increase the chances of success?

Sticking to a plan at all cost

Some runners have a plan but are a little too rigid sticking to this plan. If you have a plan, don't stick to it at all cost, and don't be afraid to deviate if you have to. If the weather conditions re warmer than expected, maybe you need to drink more. If you feel stomach discomfort just reduce intake for a while.


Many runners get excited at the expo the day or days before, buy new nutrition products and will have to find out if they work in the marathon. Stick to what you have tested and to what you know will work. Don't experiment in the most important event of the year!

Three common mistakes marathon runners make.

Why is nutrition so important for a marathon?

Let’s start with the most important questions: Why is nutrition important in a marathon and what difference can it make? A marathon will take anywhere from 2-6 hours. Energy expenditure is somewhere between 2200 and 3200 kcal depending mostly on body weight Interestingly it is pretty much unrelated to pace! A runner who uses half as many kcal per minute will be running for much longer, resulting in similar total energy use.

Problems you may run into during a marathon

Poor nutrition can mean that hypoglycemia develops and a runner will be reduced to walking the last part of the marathon, lightheaded and with little or no power left in the legs. Even if this low blood sugar does not occur fuel supply to the muscle may be suboptimal and this can affect performance.

In addition to this, and specially in warm conditions, dehydration may develop: fatigue, headaches and disorientation may be the result.

Thirdly, it is also possible that gastro-intestinal problems develop… and often we see runners on the side of the road vomiting or quickly popping into the porter loos…. The glamour of marathon running….

How can we prevent trouble and increase the chances of a great race?

How do we prevent all of this? How can we make sure we will have a great race?

Besides making sure you are well trained and well recovered at the start of a marathon, performance in a marathon is dependent on 4 main nutrition related factors:

Making sure there is adequate fuel to complete your marathon

a. Enough carbohydrate stored in muscle

b. Enough carbohydrate stored in the liver

c. Enough carbohydrate supply during the marathon

Adequate hydration

This means preventing dehydration throughout the marathon but also preventing overhydration. This is especially important in hot conditions.

Minimise the risk of GI problems

Some runners never have GI problems. They are the lucky ones. The majority of runners will experience at least some discomfort and in some cases serious GI distress. These runners should pay attention to what they eat before and take in during the marathon.

Supplements that may help

There are very few supplements that can help a marathon runner (despite what you may read and despite what companies may claim). Caffeine is the exception, so we will cover caffeine intake below.

Many nutritional factors might affect marathon running performance

Carbohydrate as a fuel

The body uses two main fuels: carbohydrate and fat. Fat is the primary fuel for less intense exercise (low to moderate intensity: often referred to as aerobic) while carbohydrates are the primary fuel for intense exercise moderate to high intensity). Someone who is well trained can burn fat at a higher rate. This will help them to be less dependent on carbohydrate, but when the intensity increases carbohydrate is still the preferred fuel. Carbohydrate can deliver energy much faster to the muscles than fats. Fat is like “diesel” and can support much longer efforts than carbohydrate. Carbohydrate, however can provide much more energy per unit of time.

Carbohydrate stores are relatively small

The body has stores of both fuels, but unfortunately the stores for carbohydrate are much smaller than those of fat. Even the leanest athlete has sufficient fat to sustain the longest races at moderate intensity (thousands of grams of fat). In fact, there would be enough fat in any athlete to run many back-to-back marathons.

The typical athlete will also have 500-800g of carbohydrates stored as muscle glycogen and perhaps 80 grams or so as liver glycogen. These stores are relatively small and can only provide a fraction of the total energy from fat stores). These carbohydrate stores would be sufficient to fuel 2-3 hours of intense exercise.

Avoid hitting the wall

Most marathon runners are familiar with “hitting the wall”. Usually around 20 miles or 32 km. This point in the marathon coincides with the depletion of carbohydrate stores.. and although it may not be the sole reason for the "hitting the wall" phenomenon, with adequate nutrition we can delay this point or even completely prevent it.

A large group of marathon runners setting off on their journey (legs only)

Sweating, temperature regulation and dehydration

We also sweat and this is an important process because it helps us to regulate body temperature. Without it we would soon overheat just like a car engine would overheat without a cooling mechanism. When fluid losses are large this will start to compromise body function. It will increase cardiovascular stress (for example increased heart rate), it will reduce the ability to regulate body temperature, and it will also increase the risk of gastro-intestinal problems. So we must make sure that we drink enough to prevent these large losses. Small losses are fine and maybe even beneficial.


This means that in the lead up to the marathon and during the marathon we must:

1. Make sure we have sufficient fuel in the muscle glycogen tank

2. There is sufficient fuel in the liver glycogen tank

3. We maintain a good level of hydration.

What to eat the day before the marathon?

In order to start a race with optimal glycogen stores it is important to eat carbohydrate-rich in the day or days before the race (It is important to also reduce the amount and the intensity of training to reduce the use of glycogen stores). Traditionally consuming additional carbohydrates has been called carbo-loading. Consuming a little more carbohydrate than normal at the expense of some protein and fat will ensure that you are filling up your muscle glycogen stores, without gaining weight. Carbo-loading seems to get confused sometimes with overeating (eating as much as possible). This is not necessary or wanted. Good sources of carbohydrate include pasta, rice, potato and bread. Extreme supercompensation diets such as those used in the 1970s are not necessary. Read more on carb loading here.

What to eat for breakfast?

When you wake up in the morning the liver is low in glycogen; the body uses up the liver glycogen through the night. Because the liver provides carbohydrate to maintain your blood sugar and prevent hypoglycemia (low blood sugar) during your race, it is essential to make sure you replenish liver glycogen. This is why breakfast is so important; breakfast replenishes liver glycogen stores. A good pre-race breakfast includes 100-200 grams of carbohydrate in the 3-4 hours before the start of your race. Some athletes find it difficult to eat before a race; they could benefit by getting their carbohydrates from drinks. Read more on race day breakfast here.

Athletes who experience stomach problems frequently should avoid breakfasts that are high in fiber, fat and protein. Individuals very prone to developing gastro-intestinal problems may also want to avoid milk products (or use lactose free products). Read more about avoiding GI problems here.

Good carbohydrate sources for race day

  • refined grains

  • white rice

  • corn/rice based cereals

  • white bread, bagels (no seeded breads)

  • pancakes

  • cooked veggies (no seeds)

  • cooked potatoes

  • ripe bananas

  • cooked fruits, apple sauce/fruit blends

  • rice cakes

  • honey

  • syrup

  • pulp-free juice

Nutrition just before the start

In the 15-30 minutes before the start you can pre-load your stomach with some fuel, without any risk of developing what is called a reactive hypoglycemia: low blood sugar because insulin and exercise both stimulate removal of glucose from the circulation (Read more about this phenomenon here). A gel is an easy way to do this but other sources are fine too. Aim for 20-30g (80-120 kcal) of carbohydrate with 90-180ml (3-6 fl oz) of water.

Food and drinks will sit in the stomach for several minutes and absorption takes a bit of time even with the fastest type of carbohydrates. Most of the carbohydrate you ingest at 10-15 min before the start will become available during the first part of the run. So, anything that is ingested shortly before the start is part of your nutrition during exercise. Make sure you also practice this in training.

Fueling during the race

Marathon nutrition requires a bit of planning. It is important to study what is available on course and develop a plan that takes into account foods and drinks you will collect on course versus foods and drinks you will have to bring yourself. During longer races your target carbohydrate intake should be higher than during shorter races. In races over 2 hours, athletes can benefit from an intake of roughly 60 grams of carbohydrate per hour. Do not try this for the first time in your marathon! You should transition from your current fueling levels towards 60g/h during training. Your gut will get used to this very quickly. Again, what foods and drinks are best is a matter of personal preference. The target of 60g/h can be achieved with many different combinations of water, sports drink, gels, chews, bars, and regular foods. More recently elite marathon runners have been ingesting 90 g/h or more. There are even reports of runners using as much as 120 g/h (Read this blog). This certainly needs a bit of preparation, but could potentially improve performance further. It is essential to ingested the right types of carbohydrate (read more here) and to practice this many times in the weeks leading up to a marathon (read more here). If you haven’t done this, this strategy should not be considered.

A helpful tool for nutrition planning

If you want a safe and solid plan that provides enough fluid, enough fuel, but not so much that it could cause GI problems, I recommend you visit This site is something we developed based on what we know from science. It will help you create your own nutrition plan, based on your specific race, your goals, your physiology and your preferences. You can even plan for different weather conditions. Read this blog to find out more about the background of this program.

Runner using the CORE Nutrition planning tool on an iPad

What are sports drinks and when do you use them?

Sports drinks typically contain carbohydrates in concentrations of 6-7%. This means that the drink contains 60-70 grams of carbohydrates per liter of fluid. A regular sports bottle of 600ml (20 oz.) will therefore deliver roughly 35 grams of carbohydrate. A sports drink also contains some sodium (and other electrolytes) which can be beneficial for the absorption of fluid (as we will see under hydration).

What are high carb drinks and when do you use them?

Some drinks are designed to have more carbohydrate. They still provide fluid but their main purpose is to fuel. These drinks are especially useful during longer events when carrying a lot of fluid is not an option. You can still carry enough carbohydrate. Some of these drinks have 90 grams of carbohydrate in a 500ml bottle.

What are gels and when do you use them?

Gels are a compact form of energy. A small volume of fluid with a relatively large amount of carbohydrates. Gels typically deliver 20-25 grams of carbohydrates and come in many different flavors. Gels may be caffeinated or non-caffeinated. The exact number of gels you need depends on your pace, the duration of exercise (race or training) and the amount of carbohydrates you get from other sources. Some gels are smaller and contain a very sticky substance, other are more liquid, are much easier to consume but are a little larger and heavier to carry.

What are chews and when do you use them?

Chews are the middle ground between bars and gels. They are more solid than gels and are usually easier to consume than bars: easier to chew and come in single bite pieces. Chews generally are 6-10g per piece, so 3 pieces typically is close to a gel. Obviously they contribute not to hydration but if you have access to water on course, this is a viable option for those who like to eat during a long run.

Carbohydrate from solid foods

Solid foods usually provide more carbohydrates per unit of weight and are therefore a very effective energy source to carry. Bars typically deliver 25-60g of carbohydrate and come in many different flavors and with varying levels of fat, fiber and protein. It is recommended to select energy bars that are low in fat, fiber and protein as these ingredients will slow down gastric emptying and may contribute to stomach problems. There are of course also other foods that can be used: ripe bananas, figs, small white bread rolls with jam, boiled potatoes and so on.

Solid food is great in preventing an empty feeling in the stomach that many athletes experience during later stages of a race. One drawback of solids, however, is that they can be difficult to chew while racing. A second drawback is that solids, especially some energy bars generally contain more carbohydrates than should be consumed at one instance; this means a bar would need to be carried for some period while being consumed in smaller bites. For these reason, some athletes prefer to get their carbohydrates from gels or chews.

The different carbohydrate sources that runners have access to, with their carbohydrate contents

Caffeine and performance

Many athletes use caffeine before or during a race to boost their performance. This practice is indeed supported by scientific evidence although there may be individual differences in tolerance and perception. Studies have demonstrated that relatively small amounts of caffeine are required to give optimal effects (3mg per kilogram body weight; 200mg for a 70kg person).

Timing of caffeine intake

Because caffeine absorption takes 30-90 minutes, timing of caffeine is important. Studies have shown that caffeine ingested late in a race can still provide benefits. What works best is going to be highly individual and best established by trial and error. There are many different ways to deliver caffeine: gels, colas, energy drinks, and coffee. The caffeine consumption for a race should conform to a person’s normal intake of caffeine. It is generally recommended not to exceed a daily intake of 400 mg caffeine from all sources.

Caffeine sources

  • Caffeinated gels 25-50mg per gel

  • Cola drinks 40-50 mg per 355 ml can

  • Energy drinks 50-100 mg per 250 can

  • Espresso 80-100 mg per cup


Another cause of fatigue during a marathon is dehydration. In order to make sure body temperature stays within acceptable limits and we don’t overheat, we sweat. The faster we run, the more heat is produced and the more we need to sweat to stay cool. In hot conditions it is even more important because sweating may be the only way we can cool down our bodies. When we lose too much sweat and become dehydrated, it becomes harder to maintain our body temperature. Some degree of dehydration is unlikely to be a problem but once you start to lose 3% of your body weight or more, performance may be affected.

Hydration plan or your marathon

In order to prevent dehydration, it is important to start a race hydrated and maintain proper hydration throughout the race. Below we will split the advice into before the marathon and during the marathon.

Before the race

Before the race, drink at least 500ml in the ~2 hours before the start; excess water will be eliminated through urine. Double check your urine color is pale.

During the race

During the race, your target for fluid intake should be such that you lose no more than 3% body weight. This will always means consuming fluid at a rate that is below your sweat rate (the longer the race, the closer to your sweat rate consumption will need to be). Drink to thirst is a recommendation that works fine for the slower athlete. If you are going a bit faster it is better to go in with a plan. It is best to measure your sweat rate regularly in training so you get a good idea of how much you sweat in different conditions. This blog explains how to do this.

Use the first part of the marathon

It is wise to use the early parts of a race when the gastrointestinal tract is working fine to absorb both carbohydrate and fluid. Later in the race, even though you may be thirsty, the gut may not absorb as much. Don’t drink excessively, and use common sense. The goal should be to lose a little weight (1-2 kg) at the finish line. Athletes who want to be a little more prepared can work out how much they will sweat in the conditions of the race and use this to guide their drinking. If you want to find out how to best measure your sweat rate visit this blog. Don’t drink excessively, and use common sense. All athletes definitely need to avoid weight gain, which clearly would be a sign of drinking too much, and that could lead to a dangerous condition called hyponatremia. Don’t forget that good hydration starts before the race, and hydrate well in the days leading to your race.

Training the gut

One of the most important aspects of preparation is “training your race nutrition”. Nutritional preparation should not start when you are walking around at the expo the day before your marathon! It should start at least 6-10 weeks before the race and is important during your entire preparation phase. Training will always involve a mix of hard and easy; same is true for nutrition. On easy days where quality of training is not so important and where you may purposely want to train your body to use fat as a fuel, you will consume little or no carbohydrate (“training low"). On other days that are hard, where quality is important and where you want to train your body to perform just like you will in a race, it is a good idea to follow your race plan. Read more about training the gut here.

Top tips

  • Don’t experiment with new products on race day.

  • Use the same nutrition products for at least 6 weeks prior to the race.

  • Don’t be afraid to listen to your gut and when fluids are not emptying from your stomach reduce the intensity temporarily. You will benefit from this later in the race.

  • Hydration during the race is important, but make also sure you don’t start the race dehydrated

  • Plan your breakfast on race day well in advance and make sure it is available for you on race day. Don’t just show up for breakfast in a hotel on race day without checking.

Related blogs

Reading list

  1. Baker LB, Jeukendrup AE. Optimal composition of fluid-replacement beverages. Compr Physiol. 4(2):575-620, 2014.

  2. Burke LM, Hawley JA, Wong SH, Jeukendrup AE. Carbohydrates for training and competition. J Sports Sci. 29 Suppl 1:S17-27, 2011.

  3. Jeukendrup AE and Gleeson M. Sports nutrition 2nd edition Human Kinetics Champaign IL. 2010 (ISBN-13: 978-0736079624, ISBN-10: 0736079629)

  4. Jeukendrup AE. Nutrition for endurance sports: marathon, triathlon, and road cycling. J Sports Sci. 29 Suppl 1:S91-9, 2011.

  5. Jeukendrup A. A step towards personalized sports nutrition: carbohydrate intake during exercise. Sports Med. 44 Suppl 1:S25-33, 2014.

  6. de Oliveira EP, Burini RC, Jeukendrup A. Gastrointestinal complaints during exercise: prevalence, etiology, and nutritional recommendations. Sports Med. 44 Suppl 1:S79-85, 2014


Recent Posts

See All



If you want to find out  the best types of protein, optimal amounts, or timing. Click here 


Want to know more about nutrition for running. Click here.


If you want to know more about supplements, the benefits and the risks. Click here.

Sports nutrition

General sports nutrition topics can be found here.

bottom of page