Amacx Sports Nutrition

What do I eat to fuel my marathon?

Oct 02, 2023
Written by: Martijn Redegeld

Planning a marathon soon? Perhaps for the first time, with the aim of completing the magical distance of over 42km? Or are you looking for the last few percent of extra profit to improve your personal record? It goes without saying that good preparation is half the battle. The right footwear and sufficient training will undoubtedly have been taken into account, but do you also have a well-thought-out competition nutrition plan ready? In this blog you can read everything you need to know to get the most out of your marathon.

In summary:
  • Start stacking carbohydrates ('carbo loading') 24 to 36 hours prior to the marathon. The starting point is approximately 10 grams of carbohydrates per kilogram of body weight per day. This ensures maximum muscle glycogen stores.
  • Provide a carbohydrate-rich and easily digestible breakfast about 3 to 4 hours before the start. The starting point is approximately 3 grams of carbohydrates per kilogram of body weight. This meal ensures a maximally filled liver glycogen store.
  • If necessary, have a small carbohydrate-rich snack 1 hour before the start, such as a ripe banana or energy bar from the Amacx Energy Line.
  • Don't forget to drink enough during the last hours leading up to the start. Check the color of your urine: if it is light in color, you know that your fluid balance is in order.
  • During the marathon, aim for 1 to 2 products from the Amacx Energy Line per hour, to achieve an intake of 30 to 60 grams of carbohydrates per hour. Gels are the most obvious choice.
  • Determine your individual sweat loss in the run-up to the marathon and adjust your fluid intake during the marathon accordingly. The starting point is to lose a maximum of 2 to 3% of body weight during the marathon. Please note: 1 to 2 sips of water every 5 kilometers at the organized supply posts will be insufficient in many cases.
  • Stacking carbohydrates for the marathon: how do you do that?
  • In terms of nutrition, the final preparation for the marathon begins about 36 to 48 hours prior to the start. The day before the marathon should be devoted to stacking carbohydrates ('carbo loading'). This ensures that the glycogen stores in your muscles, which serve as a fuel tank for the necessary carbohydrates, are fully filled. What and how much exactly you need to eat to stack carbohydrates correctly depends on, among other things, your body weight. You can read more about this in our previous blog.

Breakfast before the marathon: this is how you ensure sufficient energy

The evening before the marathon, check off the carbohydrate stacking. At that moment you know that the fuel tank in your muscles is full and that it will not be emptied before you start. This means that on the morning of the marathon you only have to replenish the (significantly smaller) glycogen stores in your liver. The body continuously draws energy from this fuel tank (including to supply the brain with fuel), which means it is partially empty after waking up. For this reason, it is advisable to have a final carbohydrate-rich meal to get the last fuel into the body (usually breakfast).

What to eat and drink before the marathon: the ideal menu

Aim for an amount of +- 3 grams of carbohydrates per kilogram of body weight. For someone weighing 70kg, this amounts to +- 210 grams of carbohydrates. To ensure that this is all digested and absorbed before the start of your race, and thus prevent stomach/intestinal complaints, it is recommended to have breakfast at least 3 to 4 hours before the start. In addition, make sure that the meal is easy to digest. Choose low-fiber products (such as white bread, corn flakes or rice porridge) and, if necessary, fill with liquid sugars (such as honey, jam and fruit juice). Avoid products that contain a lot of fats and/or proteins, such as eggs, (full-fat) dairy, cheese and meat products. In addition, do not forget to drink plenty of fluids. Aim for at least 500ml of fluid, but above all check the color of your urine. This should be relatively light in color to ensure that your fluid balance is in order. See an example below:

Marathon runner of 70kg (goal = +- 210 grams of carbohydrates)

Jam, honey, syrup, with 6 slices of white toast bread

135 grams of carbohydrates

Bowl of fruit yoghurt (200g)

25 grams of carbohydrates

30 grams of cornflakes

25 grams of carbohydrates

1 glass of fruit juice (200ml)

25 grams of carbohydrates


210 grams of carbohydrates

Take enough rest after your breakfast to properly process and absorb all the nutrients. This is crucial to avoid gastrointestinal upset during the marathon, and requires a minimum of 3 hours. If you want to eat something small in the run-up to the start, choose a light, carbohydrate-rich snack. This can be a ripe banana, but also an energy bar such as the Amacx Fast Bar or Energy Nougat. Don't forget to drink enough in the last hours before the start. Check the color of your urine several times to see if your fluid balance is in order. If it is light in color, you know that you have drunk enough.

Nutritional strategy for the marathon: this is how you ensure sufficient energy and prevent stomach and intestinal complaints

As soon as the starting gun has sounded, your competition nutrition plan comes into effect. The most important principles are:

  1. Have a competition nutrition plan. Eat and drink at the planned times, even if you feel better than expected or you are not hungry or thirsty. Try to stick to this plan, but don't forget to make minor adjustments if necessary (for example if it gets warmer than planned, or if you unexpectedly suffer from stomach or intestinal complaints). Practice this competition nutrition plan regularly to train your stomach and intestines to process these nutrients during exercise!
  2. Be well prepared and avoid any surprises. So make sure you have access to the products you have trained with and that you know you tolerate well. Know where the organization's supplies are and what is provided here. If you need other products or things at other times, please arrange this yourself.

    Carbohydrates during the marathon: this is how you ensure sufficient energy

    During the marathon, aim for a carbohydrate intake of at least 30 to 60 grams of carbohydrates per hour to ensure that the fuel tank in your muscles does not become depleted. Once these glycogen stores are depleted, you will experience the well-known 'hunger pangs'. Therefore, try to take an Amacx product from the Energy Line regularly, 1 to 2 times per hour. The most obvious option is to take an Amacx Drink Gel once every 30 to 60 minutes. These gels are very easy to digest, provide energy very quickly and can be consumed without additional water. However, if you prefer one of the bars from the Energy Line, or Energy Drink, this can of course also provide the necessary fuel.

    In addition to energy (carbohydrates), your body also needs sufficient fluid. This is important to compensate for sweat losses. By continuing to drink enough you will prevent significant loss of performance in the last part of your marathon. How much you should drink depends greatly on your individual sweat production and the ambient temperature. The starting point during a marathon should always be to lose a maximum of 2 to 3% of your body weight through sweating. Someone weighing 70kg will therefore be able to lose a maximum of about 2.1kg during their marathon before serious performance loss occurs.

    Therefore, try to measure your sweat loss in advance during the heavier training sessions in the following way:

    1. Weigh yourself shortly before the start of the training, without clothing and preferably after you have gone to the toilet.
    2. Do your training as always. During training, write down exactly how much you eat and drink. Also record the temperature and humidity.
    3. Immediately after training, dry the sweat from your body, go to the toilet again and weigh yourself again.

      Preparation is key

      Don't forget that a balanced diet, tailored to your training schedule, also offers great added value earlier in the preparation. This will allow you to make more progress with each training and ultimately arrive at the start of the marathon in even better shape. In the run-up to the marathon, do not forget to train your competition nutrition plan during some longer/heavier training sessions (or, for example, a half marathon that you run in preparation). This is necessary to train your stomach and intestines to absorb and process the required nutrients during exercise, without resulting in stomach or intestinal complaints. You can read more about this in our previous blog.

      Normally you will lose weight during a tough workout. For example: an athlete weighs 70kg before training, he drinks a 500ml water bottle during the 1.5 hour training and still weighs 69kg afterwards. His net sweat loss under these conditions is 1 liter, or 0.67 liters per hour. If the expected finish time of this runner is around three hours, he will lose a total of +- 2 liters of sweat and he will remain within his individual margin if he drinks 500 ml per hour. However, if the expected end time is 4 hours, the total sweat loss will increase to +- 2.7 liters. This would mean that a fluid intake of 500ml per hour is insufficient, and the runner should aim to drink around 150ml extra every hour to stay within their limits.

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