Do You Need to Carb Load for a Half Marathon?

Mention a half marathon and someone will tell you to carb load. Then you hear about marathon runners eating mountains of pasta for three days and wonder if you should do the same for 13.1 miles. The short answer is: probably not the full version, but for most beginners a little planning the day before does help. It all comes down to how long you will be out on the course. Here is an honest answer by finish time, a simple day-before plan and race-morning breakfast ideas.

What is carb loading, and why does it matter?

Your muscles store carbohydrate as glycogen, and it is your main fuel when you run at a steady or hard effort. Those stores are limited. For many runners they are roughly enough for about 90 minutes of solid running before they start to run low, which is when legs can feel heavy and pace can drop.

Carb loading simply means eating more carbohydrate than usual in the day or two before a race, while you are training less, so your glycogen stores are as full as possible on the start line. Older methods started with a depletion phase of hard training and very low carbs. Research has since suggested this is not needed: a high-carb diet combined with lighter training for a day or two appears to top up stores well.

Sports nutrition guidelines generally reserve full carb loading, around 10 to 12g of carbohydrate per kg of body weight per day for 36 to 48 hours, for events lasting longer than 90 minutes. For shorter events, they suggest a lighter fuelling-up approach of roughly 7 to 12g per kg over the previous 24 hours, which for many regular runners is close to a normal training day.

So, do you need to carb load for a half marathon?

It depends on your likely finish time. Treat this as a starting point rather than a strict rule, because body size, pace and how your stomach copes all make a difference.

Why the split? If you finish in under 90 minutes, your glycogen stores should mostly cover the distance, provided you have been eating normally. One older study in trained runners found carb loading did not improve their times over a race of roughly half marathon distance. If you will be running for two hours or more, you are well past that 90-minute mark, so arriving with full stores, and adding some carbs on the way round, makes more sense.

The honest middle ground for most first-timers: you do not need a marathon-style, three-day eating plan. A well-planned day before, plus a good breakfast, covers most of what you need.

How much carbohydrate should you eat the day before?

The guideline numbers are based on body weight. For a 70kg runner, 7g per kg works out at about 490g of carbohydrate across the day, and a full 10g per kg load would be about 700g. That second figure is a lot of food, and if it leaves you bloated and sluggish it can do more harm than good.

So rather than chasing an exact number, aim to eat noticeably more carbohydrate than usual, spread across the whole day, from foods you already know sit well with you. If you like numbers, somewhere around 7g per kg is a sensible target for a first half. If you expect to be out for well over two hours and your stomach copes, you can push a little higher with an extra snack or a carb-based drink.

The other half of the trick is swapping, not just adding. Because you are eating more carbs, ease off on fibre and fat so the total amount of food stays manageable. White bread, white rice, pasta, potatoes without skins, bagels, crumpets and low-fibre cereals are all easy on the stomach and quick to eat.

What does a simple day-before plan look like?

Here is an example for a 70kg runner with a Sunday morning race. The carb figures are rough and depend on brands and portion sizes, so check labels if you want to be precise. Scale portions up or down for your size.

That adds up to roughly 465g to 505g, or around 7g per kg for a 70kg runner. Notice that lunch is the biggest meal, not dinner. Eating your largest plate earlier gives it time to settle, so you are not going to bed stuffed. Keep your evening meal simple and familiar.

What should you eat on race morning?

Breakfast tops up the carbohydrate stored in your liver, which runs down overnight, so do not skip it, even if nerves make eating feel like a chore. Guidelines suggest around 1 to 4g of carbs per kg in the 1 to 4 hours before a race longer than an hour. For most beginners, a familiar breakfast eaten two to three hours before the start is the sweet spot. For a 9am start, that means eating at around 6 to 7am.

Good race-morning options include:

• Porridge with a banana and honey
• A bagel with jam or honey, and a banana
• Two slices of white toast with jam, plus a small glass of juice
• A low-fibre cereal with milk and a banana

Keep fat and fibre low, and have your usual coffee or tea if you normally do. If there is a long wait before the start, a small top-up 30 to 60 minutes before, such as half a banana, a few jelly sweets or a gel you have used before, can help you feel ready. Most importantly, rehearse this breakfast before one or two long training runs so you know it works for you.

Do you need gels during a half marathon?

Carb loading and fuelling during the race work together. Guidelines suggest around 30 to 60g of carbohydrate per hour for efforts lasting roughly one to two and a half hours. A typical gel contains somewhere around 20 to 30g, so check the label on yours.

If you are finishing in under 90 minutes, gels are optional. A study of highly trained runners found taking carbohydrate gels during a half marathon made only a trivial difference to their times. If you will be out for two hours or more, regular carbs are more likely to help. Many runners take a gel every 30 to 45 minutes, starting about 45 minutes in, with a few sips of water. Practise this on your long runs first, because a new gel on race day is a common cause of stomach trouble.

What are the most common carb-loading mistakes?

• One giant pasta dinner. Squeezing all your extra carbs into one late meal leaves you uncomfortable and can disturb your sleep. Spread them out.
• Loading up on fibre. Wholemeal everything, beans, lentils and big salads are great most of the time, but not the evening before a race.
• Adding lots of fat. Creamy sauces, cheese-heavy dishes and fried food fill you up without adding much carbohydrate.
• Trying something new. A new restaurant, new gel or new breakfast is a gamble. Stick to foods you have tested.
• Panicking about the scales. Your body stores water alongside glycogen, so feeling slightly heavier the morning of the race is normal and expected.
• Alcohol. Save the celebration drink for after the finish line.

How does Edge help you get to race day ready?

Fuelling is only half of the story. You also need training that builds you up steadily and a lighter race week so your legs, and your glycogen stores, are fresh on the day. Edge is a free fitness app, and Edge Pro builds a fully personalised plan across running, strength, HIIT and mobility, ready within 24 hours, so your strength sessions and runs sit together in one plan instead of competing with each other.

With Edge Pro you can message a real coach anytime, so if you are unsure how race week should look, or how to fit your long runs and fuelling practice around a busy week, you can just ask. Edge syncs with Strava, Garmin, Apple Health and Coros, and Edge Pro is from £19.99 a month with a free 7-day trial. 20,000+ members already train with Edge.

This article is general guidance, not medical advice. If you are new to exercise, returning from injury, pregnant, or managing a health condition, speak to your GP before starting, and see a physio for any niggle that does not settle.