Should You Carb Load Before a Half Marathon or Marathon?
The week before a big race, you'll hear runners talking about one thing almost as much as their target time:
Carb loading.
For some, that means an enormous bowl of pasta the night before the race.
Others spend several days eating everything from bagels and rice to sweets and sports drinks.
But what does carbohydrate loading actually mean? Do you need to do it for a half marathon? And how much carbohydrate should you be eating before a marathon?
Here's what runners need to know.
What Is Carb Loading?
Carbohydrate loading is a nutritional strategy designed to increase the amount of carbohydrate stored as glycogen in your muscles before prolonged exercise.
Your body stores carbohydrate primarily as glycogen in your muscles and liver.
During running, particularly at moderate-to-high intensities, carbohydrate provides an important source of energy.
The problem is that your glycogen stores are limited.
As exercise continues for several hours, those stores can become significantly depleted.
Carbohydrate loading aims to begin your race with your muscle glycogen stores as well stocked as possible.
Is Carb Loading Just Eating Loads of Pasta?
Not quite.
The traditional image of carb loading is an enormous pasta dinner the night before a marathon.
There's nothing inherently wrong with pasta, but one giant meal isn't really the point.
An effective carbohydrate-loading strategy involves increasing your carbohydrate intake over the period leading into a prolonged endurance event while your training volume is reduced.
Rather than trying to consume everything at dinner the night before, spreading your carbohydrate intake across regular meals, snacks and drinks can make the process considerably easier.
How Much Carbohydrate Do You Need to Carb Load?
Sports nutrition guidelines commonly recommend approximately 10–12g of carbohydrate per kilogram of body weight per day for around 36–48 hours when the aim is to maximise muscle glycogen stores before prolonged endurance exercise.
That's a lot of carbohydrate.
For a 60kg runner, 10g/kg would equal approximately:
600g carbohydrate per day
For a 70kg runner:
700g carbohydrate per day
For an 80kg runner:
800g carbohydrate per day
This is why proper carbohydrate loading looks very different from simply eating an extra portion of pasta.
However, these are performance-focused guidelines for maximising glycogen availability — not a rule that every recreational runner must force themselves to achieve.
Your race distance, expected finishing time, body size, usual diet and gastrointestinal tolerance all matter.
Do You Need to Carb Load for a 5K or 10K?
Generally, no.
If you're eating a normal carbohydrate-containing diet and racing for less than approximately an hour, a dedicated carbohydrate-loading protocol is unlikely to be necessary.
That doesn't mean your pre-race nutrition doesn't matter.
You still want to arrive at the start line appropriately fuelled.
But dramatically increasing your carbohydrate intake for two days before a 5K or 10K generally isn't required.
Should You Carb Load for a Half Marathon?
This depends partly on how long you expect to be running.
A competitive runner completing a half marathon relatively quickly has different requirements from someone who will be exercising for well over two hours.
Increasing carbohydrate availability before a half marathon can certainly be useful, particularly for runners expecting a longer finishing time.
However, you don't necessarily need to approach it with the same aggressive carbohydrate-loading strategy you might use before a marathon.
For many recreational runners, the practical goal should be:
Arrive at the start line with good glycogen availability without upsetting your stomach trying to force excessive quantities of food.
That might mean increasing the proportion of carbohydrate in your meals during the day before the race and ensuring you're eating consistently.
Should You Carb Load for a Marathon?
This is where carbohydrate loading becomes particularly relevant.
A marathon will typically involve several hours of continuous exercise.
Starting with well-stocked glycogen stores gives you a larger carbohydrate reserve before you begin relying heavily on the fuel you're consuming during the race.
For runners looking to maximise carbohydrate availability, the final 36–48 hours before the marathon are particularly important.
At the same time, your training volume will normally have fallen considerably because you're tapering.
That combination — higher carbohydrate availability alongside reduced training demand — allows your body to increase muscle glycogen stores before race day.
What Foods Should You Eat When Carb Loading?
Carb loading doesn't mean you have to eat exclusively pasta.
There are plenty of carbohydrate-rich foods you can use.
For example:
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Rice
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Pasta
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Bread
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Bagels
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Potatoes
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Cereal
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Oats
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Pancakes
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Fruit
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Fruit juice
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Rice cakes
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Pretzels
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Low-fat baked goods
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Sports drinks
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Carbohydrate drink mixes
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Familiar sports nutrition products
The key word there is familiar.
The days before your marathon aren't the time to completely reinvent your diet.
Choose foods you already know agree with you.
Why Lower Fibre Can Help Before a Marathon
Eating large quantities of carbohydrate means eating a large quantity of food.
If all of that food is also extremely high in fibre, your digestive system may not thank you on race morning.
Temporarily choosing some lower-fibre carbohydrate options can make it easier to increase carbohydrate intake without dramatically increasing the total volume of food passing through your digestive system.
For example, some runners may swap:
Wholegrain bread → white bread
Brown rice → white rice
Very high-fibre cereal → lower-fibre cereal
Large quantities of vegetables → smaller portions
This isn't because those foods are normally “better” or “worse”.
It's simply a short-term strategy around competition.
If you know you're particularly prone to stomach problems while running, our guide to cramping, heavy sweating and stomach issues goes into this in more detail.
Don't Forget That Drinks Can Provide Carbohydrate
One of the biggest practical challenges with carbohydrate loading is simply consuming enough food.
Drinks can make that easier.
Options such as:
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Fruit juice
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Sports drinks
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Carbohydrate drink mixes
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Smoothies
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Other familiar carbohydrate-containing drinks
can contribute carbohydrate without requiring another large plate of food.
Sports nutrition can also be useful here — not because you need specialist products to carb load, but because they're convenient.
Our energy gels and running nutrition collection includes gels, chews and carbohydrate drink options that can form part of a broader race-week nutrition strategy.
What About Protein and Fat?
You don't need to eliminate either.
Protein should still form part of your normal meals.
The practical issue is that if you're trying to substantially increase carbohydrate intake while eating the same amount of everything else, the sheer volume of food can become enormous.
During a dedicated carbohydrate-loading period, carbohydrate therefore becomes the nutritional priority.
Very high-fat meals can also be extremely filling and may make it harder to consume the amount of carbohydrate you're targeting.
Think:
Increase carbohydrate — don't simply increase everything.
Will Carb Loading Make You Gain Weight?
Possibly — temporarily.
And that's completely normal.
When your body stores glycogen, it also stores water alongside it.
As your glycogen stores increase, your body weight can therefore increase before the race.
That doesn't mean you've suddenly gained a significant amount of body fat.
If you step on the scales the morning before your marathon and you're heavier than usual after increasing carbohydrate intake, don't panic and start restricting food.
Arriving at a marathon slightly heavier with well-stocked glycogen stores is very different from arriving lighter because you've under-fuelled yourself.
Should You Have a Huge Dinner the Night Before?
Probably not.
Trying to cram an enormous amount of food into your final meal can leave you feeling bloated and uncomfortable.
Ideally, you've already been increasing carbohydrate intake throughout the previous day or two.
Your evening meal can then be a normal-sized, familiar, carbohydrate-rich meal rather than an eating competition.
For example:
Rice + chicken + a familiar sauce
Pasta + a relatively simple sauce
Potatoes + lean protein
The exact meal isn't particularly important.
What matters is that it's familiar, carbohydrate-rich and agrees with your stomach.
What Should You Eat on Marathon Morning?
Your pre-race breakfast is the final part of your pre-race fuelling strategy.
For an important endurance event, runners commonly eat their main pre-race meal approximately 2–4 hours before starting, depending on individual tolerance.
The meal should generally be:
Carbohydrate focused
Familiar
Easy for you to digest
Potential options include:
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Porridge with banana and honey
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Toast or bagels with jam
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Cereal with milk
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Pancakes
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Rice
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Banana
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Sports drink
The perfect breakfast is the one you've already successfully tested before long training runs.
Don't suddenly decide marathon morning is the perfect time to experiment with a completely different breakfast.
What About a Gel Before the Start?
Some runners include carbohydrate shortly before starting.
That might mean a gel or another easily consumed carbohydrate source in the final 15–30 minutes before the race.
Whether that's useful for you depends on your overall strategy and what you've practised.
If you're unsure about when to take gels or how many you might need, read our guide to energy gels: how much and when should you take them.
Remember that this is only the beginning.
For a marathon, you'll still need a plan for consuming carbohydrate throughout the race.
Our guide to how to fuel your runs for a 10K, half marathon and marathon explains how carbohydrate requirements change as race duration increases.
Don't Forget Hydration
Carbohydrate loading doesn't replace your hydration strategy.
You should also arrive at the start line appropriately hydrated.
That doesn't mean drinking enormous quantities of water the night before or on race morning.
Your hydration requirements depend on your normal fluid intake, environment and individual sweat losses.
If you're unsure about sodium and electrolytes, read our guide to why sodium is crucial for running performance.
Practise Your Carb Load
Just like gels, shoes and race-day clothing, your carbohydrate-loading strategy can be practised.
Before an important long training session or preparation race, try a smaller rehearsal.
Pay attention to:
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How much food you're comfortable eating
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Which carbohydrate sources work well
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Whether lowering fibre helps
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How your stomach feels
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Your evening meal
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Your breakfast timing
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How you feel during the run
By marathon week, you shouldn't be guessing.
A Simple Carb-Loading Checklist
Before your marathon:
36–48 hours before: Increase your carbohydrate intake significantly if you're using a full carbohydrate-loading strategy.
Spread it out: Use meals, snacks and drinks rather than relying on one enormous dinner.
Choose familiar foods: Race week isn't the time for experimentation.
Consider lower-fibre options: Particularly if you're prone to gastrointestinal problems.
Keep drinking normally: Don't deliberately dehydrate yourself or force excessive quantities of water.
Eat a familiar pre-race breakfast: Ideally something you've already tested.
Have your during-race nutrition ready: Carb loading doesn't remove the need to fuel during a marathon.
The Takeaway
Carbohydrate loading is more than eating a massive bowl of pasta the night before a race.
The goal is to increase your muscle glycogen stores before prolonged endurance exercise, giving you greater carbohydrate availability when you start.
For shorter events such as a 5K or 10K, dedicated carbohydrate loading generally isn't necessary.
For a half marathon, increasing carbohydrate availability can be useful, particularly if you'll be running for a longer period.
For a marathon, a structured carbohydrate-loading strategy during the final 36–48 hours can be particularly valuable.
If you're aiming to maximise glycogen stores, sports nutrition guidelines commonly recommend approximately 10–12g of carbohydrate per kilogram of body weight per day during that period — although not every recreational runner needs to force themselves to the maximum end of the recommendation.
The most important thing is to practise your strategy, use familiar foods and arrive on the start line well fuelled without upsetting your stomach.
Then your during-race nutrition takes over.
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