An appropriate diet filled with the right nutrients is an essential part of any exercise routine, and fuelling optimally is especially important for endurance events like marathons or triathlons. Follow these tips to make sure you’re the one bounding over that finish line.


Check out the London Marathon's training and meal plans. Don't have a spot to run this year? You can still take part with the virtual event London Marathon MyWay – join up for your chance to run 26.2 miles on marathon day, 21st April 2024.

Next, discover what to eat for heavy training days and before swim and cycle, as well as all our marathon meal plans. Plus, read Mo Farah's tips for success.

People running a marathon

How should I nutritionally prepare for a marathon?

By now you should have trialled various energy gels, sport’s drinks and high-carb foods and have tested different pre-run breakfast and dinner options. Your nutrition plan needs to kick in at least eight weeks before the big day because you need to experiment with the food or products that work best for you as well as calculate how many gels you’ll need to keep your energy levels primed and your body optimised; you’ll also need to understand how much water you’ll need to take on to stay hydrated.

What, when and how much you eat and drink during a marathon can make or break your race. Failing to fuel properly may result in you 'hitting the wall,' a condition that is every distance runner's fear. It might sound like an old wives' tale, but it's a phenomenon that can happen to anyone, no matter how much training they've done. It occurs when the body's carbohydrate fuel tank - the body's preferred energy source during high-intensity activity - gets low and the brain and muscles show signs of fatigue. If you hit the wall during a marathon you'll know about it, every step feels like wading through treacle.

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You can take steps to avoid the dreaded wall by 'carb-loading' before and during a run to maximise your energy stores, which means stocking up on carb-rich foods as well as energy gels and sports drinks. Failing to drink enough as well as replenishing electrolytes if you need them, may leave you experiencing gastric distress, nausea and dizziness. What this means is you need to plan ahead and practice your nutrition strategy, so that on the big day your execution is perfect.

If you've still got some time before the big race, read our guide on what to eat when training for a marathon.

What factors influence my specific nutritional needs?

Your body mass and build, capacity to use fuel especially carbs, your ability to maintain adequate hydration despite the intensity of the exercise and the environment, and your age are all factors that will influence how you will need to fuel during the race. Understanding your specific needs are important because if the glycogen stores of your muscles reach a low level your exercise intensity and performance will be impaired.

How should I fuel during the marathon?

Your body fuels high-intensity, long duration activity with carbs and uses glycogen stores to maintain performance. For this reason, it's important to replenish your all-important glycogen stores during runs of 60-90 minutes or more. It's important to be aware the body can only store around 2,000 kcals of carbs (500g) and after a few hours of running at 55-75% of your maximal heart rate, your fuel tank warning light will flicker on unless you regularly top up your carb stores.

Exactly how much you need to refuel will be unique to you but, as a general guide, runners should aim for 30-60g of carbs per hour for the first 3 hours of their marathon, increasing to 60-90g per hour after that.

Useful options to help keep carb stores primed include:

  • Energy gels and chews that contribute 25-30g of carbs per serving
  • Sports bars that contribute 45g
  • Trail mix providing about 30-40g carbs per serving
  • High-GI foods that supply a fast release source of energy such as a large banana (24g carbs), handful of dried fruit (20g) or gummy sweets like a handful of jelly beans (17g)

Sports products vary so check labels and familiarise yourself with the brands you like – it's important to know how many of these products you’ll need to reach your hourly target. When consuming these products do so over a 4-5 minutes period and not in one go, this will aid absorption and be easier on your digestive system.

You can start taking on nutrition in the first 30 minutes of the race and then set an alert on your running watch to remind you to top up every 30-50 minutes after that.

How much water should I take on during the marathon?

Like your nutrition, your hydration needs are unique to you and will depend on your sweat rate, age, sex and build as well as the intensity of your pace and the climate and temperature you’re running in. Maintaining adequate hydration is important for so many aspects of your performance including regulating body temperature and maintaining blood volume. If your fluid levels wane, you’re likely to experience fatigue as well as muscle cramping and headaches along with the obvious signs of dehydration, such as a dry mouth.

Generally speaking, most runners need between 300-800ml per hour of the race, but it’s also worth making sure you’re well hydrated before you hit the start line with about 400-600ml drunk over the couple of hours prior to the whistle.

During prolonged exercise of 90 minutes or more, combined carb-electrolyte hydration drinks may be used to sustain carb stores and hydration.

What should I avoid eating or drinking during the marathon?

You should avoid any food or drink that you have not trained with, this is because they may affect your digestion and upset your stomach. You also may not be familiar with their carb contribution, so they may impact your fuelling strategy and energy levels.

Foods rich in protein take longer to digest, for this reason they can sit heavy in your stomach and impact your performance. It's the same with the peanut butter sachets, the protein and fat content makes them more suited as a post-run option. Fibrous foods are also slow to digest and may leave you feeling bloated and uncomfortable.

What should I focus on once I cross the finish line?

Blueberry smoothie in a tall glass

You have a window of around 30-60 mins when the body is primed to replenish its carbohydrate stores and soak up muscle-repairing protein.

Chocolate milk offers a useful combo of protein and carbs, or a smoothie with lots of fruit. Drinking plenty of fluids will help replace fluids lost through sweat.

Looking for some inspiration? Get recipes and training tips from our marathon meal plans.

Now you know what to eat during your race, get the rest of your training nutrition right:

What to eat before a run
Carb-loading explained
See all our marathon meal plans
How to stay hydrated

Will you be racing in a marathon this year? Tell us your top tips for training and how you're getting on below.

This article was reviewed on 13th December 2023 by Kerry Torrens.

Katie Hiscock is a fitness writer with diplomas in personal training and sports massage therapy. With an interest in sports nutrition, antenatal exercise and injury prevention, she works as a therapist for Brighton & Hove Albion.

Kerry Torrens BSc. (Hons) PgCert MBANT is a registered nutritionist with a post graduate diploma in Personalised Nutrition & Nutritional Therapy. She is a member of the British Association for Nutrition and Lifestyle Medicine (BANT) and a member of the Guild of Food Writers. Over the last 15 years she has been a contributing author to a number of nutritional and cookery publications including BBC Good Food. Find her on Instagram at @kerry_torrens_nutrition_


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