November 22, 2022

How To Fuel Your Next Marathon

You must fuel properly to run a fast marathon and achieve your best result. Learn how to do that in this article.

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So, you have a marathon coming up, and you want to avoid messing it up and putting all your training to waste. That’s smart.

But how do you do that?

First, you must pace your race correctly to look after your muscles, and second, you must fuel properly to have the energy to fuel them.

We won’t get into pacing in this article, but we will tackle fuelling. Fuelling is made up of two primary areas.

  1. Energy
  2. Hydration

Let’s start with energy.


When you line up on race day, you have 1,500 – 2,000 kcal of carbohydrates stored in your muscles and liver as glycogen. As you race, these stores will deplete, so you must take in external energy sources to ensure they’re not entirely exhausted and make you hit the wall.  

As a guideline, you should consume approximately 30 – 90 grams of carbohydrates per hour, depending on how fast you are.

  • < 4 hour marathon: 60 – 90g
  • > 4 hour marathon: 30 – 60g

Alternatively, you can aim for around 1g of carbohydrate per kilogram of body weight. Precision Fuel & Hydration has this handy little calculator you can use as a starting point for determining your energy needs.   

The main ways to consume energy during a race are as follows:

  1. Gels.
  2. Sports drinks.
  3. Solid foods.

For most races, we encourage you to use gels. Solid foods are hard to digest at race pace, and sports drinks often try to address too many things at once – energy, volume and electrolytes — the last two we’ll discuss in the hydration section of this article. 

Here are some examples of popular gels. My personal favourites are the two at the top:  

  • PF 30 Gel by Precision Hydration (120 kcal, 30g carbs, 0mg salt).
  • KODA (Banana) (117 kcal, 29.8g carbs, 36mg salt).
  • Maurten Gel 100 (100 kcal, 25g carbs, 85mg salt).
  • GU Roctane (100 kcal, 21g carbs, 125mg salt).
  • High 5 (91 kcal, 23g carbs, 50mg salt).
  • SIS GO (87 kcal, 22g carbs, 300mg salt).

Practise taking in energy during your long runs in the final weeks of your programme (combined with water or a sugar-free electrolyte drink) to find your sweet spot for carbohydrate tolerance.  

By race day, you should know how many carbohydrates you can comfortably stomach and how many gels you’ll need to consume to give you the desired feeling and energy you want throughout the race.

Cut Race Times, Not Corners.

Racing at your potential and enjoying training is easy when you’re following the right programme.


The second part of the fuelling puzzle is hydration. When it comes to hydration, there are a few things that you need to consider.  

  1. Sweat rate – how much sweat you lose per hour (volume).
  2. Sodium loss – how much sodium you lose in your sweat (electrolytes).
  3. The length and intensity of your race.

Knowing these numbers makes it easy to customise a hydration plan that will improve your training and recovery quality.  

As a side bonus, you’ll also lower your likelihood of suffering from muscle cramps.  

Sweat Rate

Sweat rate refers to the amount of sweat (volume) you lose per hour and varies from person to person, thanks to genetics. External factors such as temperature and humidity, clothing choices and acclimation to heat all play a role in determining how fast and how much your body sweats.

The simplest way to address sweat rate during a marathon is to drink water to thirst. Every athlete is different, but, as a rule of thumb, very few runners can comfortably drink much more than 750ml (24oz) per hour – especially when running hard – so unless experience tells you otherwise, it’s unlikely you’ll need to drink more than that. Listen to your body and drink water as needed.

Sodium Loss

A 2015 study found that athletes who adequately replaced the sodium lost in their sweat finished a middle-distance triathlon an average of 26-minutes faster than those who didn’t.  

That’s substantial!  

Based on data from Precision Fuel & Hydration, people lose between 200mg/l and 2,300mg/l of sodium, with the average person losing 949mg/l in their sweat.

The sodium you lose in sweat is genetic and changes little, if at all. Do a Sweat Test at our lab or visit Precision Hydration’s other test centres if you’re not in Singaopre to determine what you lose.  

If that’s not possible, take their free online sweat test or use the average sodium loss (949mg/l) to calculate how much sodium you should consume.

Maintaining the sodium levels in your blood is crucial to performing at your best when you’re working hard. Sodium helps you absorb and retain fluid, which keeps your blood volume up, reducing cardiovascular strain, fatigue, and potentially helping you avoid cramps.

Only drinking water when sweating over long periods dilutes your sodium levels, which can really impact your performance and could lead to hyponatremia.

Pulling It All Together

Once you have a rough plan of what you think you need to fuel your race adequately, it’s time to practice.  

Training, particularly during your long sessions in the final 8-weeks of your programme, is the most valuable time to practice your fuelling plan. Secondary races are also great opportunities to test your strategy in race conditions, where adrenaline and race intensity could throw a spanner in the works.  

You need to determine what works for you and what doesn’t to refine things as you move towards race day. I wish you well. One final reminder – never try anything new on race day.

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Ben Pulham

Ben Pulham is the founder of Coached, a personalised training programme that helps runners & triathletes optimise, track and enjoy their training.