Don’t be afraid of carbs, especially during marathon build-up.


If you want to perform your best on marathon day, whether making it to the finish line for the first time or chasing a personal best, you must fuel for success.

You should carbohydrate load (carb load) to increase glycogen stores in your muscles. This is your main energy source during the race, so you will need as much fuel as possible.

Not sure how to get started? Don’t worry. This article explains what carb loading is, how to do it, and more, with some advice from sports dietitians.

In this article, we cover:

  • What carb loading is and how to do it  
  • How many days before a marathon to start increasing carbs 
  • The best foods for carb loading 
  • How to master your race day nutrition 

What is carb loading?

Carb loading is when you eat more carbohydrates in the final 2-3 days before an endurance event, such as a marathon. 

When you eat more carbs, you fill glycogen stores in the muscles. During aerobic exercise, your body uses this glycogen as fuel. This allows you to run further with more intensity. 

It’s similar to filling your car with petrol before a long journey – you want to make sure you have enough fuel to get to the end of the marathon. 

Muscle glycogen is a key fuel for training and racing a marathon. 

When carb loading, you should also reduce your mileage 4 to 5 days before the event.

How long before a marathon should I carb load?

Increase carbohydrate intake 36-48 hours before a marathon. Aim for 10-12 grams of carbs per kilogram of body weight a day, as recommended by one study.

For example, if you weigh 70kg, eat between 700-840g of carbohydrates a day.

Additionally, you want to eat more carbohydrates between training sessions, especially in the final weeks of training. Why? Restoring muscle glycogen stores ensures you can train and recover optimally between runs and workouts.

Make sure to consume plenty of protein for muscle recovery as well. The American College of Sports Medicine recommends between 1.2-2g/kg/day. 

Using our 70kg example, aim for 84-140g of protein.

What is the best carb load meal before a marathon?

For starters, avoid trying something new. Now is not the time to try seafood for the first time (thankfully, I’m not talking from personal experience). The last thing you want is an upset stomach before or, worse, during the race.

Stick to complex carbs – your pasta, rice, potatoes, couscous, and quinoa. Pair your carb choice with a lean protein, such as grilled chicken or turkey, or white fish, such as cod. 

Example carb load meals before a marathon include:

  • Spaghetti and grilled chicken breast with a marinara sauce 
  • White rice, grilled salmon, and steamed veg
  • Homemade pizza (include a source of protein)
  • Tofu, roasted vegetables and pasta 

You can eat simple carbs leading up to the marathon, but do your best to prioritise complex carbs.

Simple carbs spike your blood sugar and, when consumed in excessive quantities, may leave you feeling tired and lethargic – quite the opposite of how you want to feel before a marathon. 

Despite this, if you struggle to eat the recommended number of carbs (e.g., 600g) daily, simple carbohydrates can help you achieve this much easier. 

Simple cars are also great options during your race for that quick boost of energy and to replenish your glycogen stores to push you to the finish line. 

Avoid fibre-rich foods to prevent GI (gastrointestinal) discomfort and stomach upset. Additionally, spread your meals throughout the day as evenly as possible. This will make it easier to hit your recommended carbohydrate intake without a last-minute binge.

How to fuel your marathon training 

Carb loading before a marathon helps you perform at your best. But many runners don’t fuel their training with as much dedication or intention.

Fueling correctly for your training helps you optimally recover between sessions and workouts with the right intensity to get the necessary adaptations to improve.

As a general rule of thumb, you want to eat plenty of carbs during training, especially when running high mileage weeks.

Moreover, eat plenty of protein to ensure optimal recovery and eat a mix of fruits and vegetables (the more varied the colour, the better) to provide essential micronutrients for overall health and wellbeing.


Read our marathon nutrition guide for more advice on what to eat in the marathon build-up. 

How to fuel on race day

“The last 10K of the marathon is notoriously challenging for runners as this is often where fatigue sets in and the wheels fall off. There can be a number of reasons why this occurs. 

Often, it’s because muscle glycogen stores are depleted. Depleted glycogen stores in those last six miles of the marathon are usually linked to inadequate fueling during the prep for the marathon and in the earlier miles of the race.

Start with doing a carbohydrate-loading protocol before race day to load up your muscle glycogen stores. Then, during the race, aim to fuel regularly and early in the race to spare muscle glycogen and delay fatigue in those final miles of the marathon,” says Alex Larson, a registered dietitian and nutritionist for endurance athletes.

Fueling and carb loading before the marathon is vital. But you also need to eat and drink on race day to replenish your glycogen stores for maximum performance and to stop you from “hitting the wall.”

Aim for 30-60g of carbohydrates per hour on race day. Most runners prefer using energy gels as these usually contain 30g per gel – two of these/hour allow you to easily replenish your glycogen stores.

Moreover, hydration is often overlooked. Alex Oskian, MS, RDN, and nutrition coach at Working Against Gravity, suggests consuming liquid every time you consume a carb source during the race. She recommends practising this in your training. 

You also need to drink plenty of fluids leading up to the marathon. Drinking plenty will aid digestion, promote recovery, and prepare your body for fluid loss (sweat) during your race.

Key takeaways

  • Carb loading increases muscle glycogen stores (energy for race day)
  • Start increasing carb intake 36-48 hours before the marathon 
  • Aim for 10-12g/kg/day bodyweight of carbs (e.g., a 70kg person would require 700-840g of carbs a day
  • Prioritise complex carbs (rice, pasta, potatoes), but use simple carbs or drink your carbs if needed
  • Consume energy gels, bars, chews, and sweets during the race 

FAQs

Should you carb load the night before a competition?

Don’t leave it until the night before! You should start carb loading 36-48 hours before competition to replenish and load your glycogen stores fully.

Is rice or pasta better for carb-loading?

Both white rice and pasta are great choices for carb loading. Choose whichever you prefer more/does not provide GI upset.

How many gels for a marathon?

You can take anywhere from 4-8 gels during a marathon. Everyone is different, and their GI will respond differently. You may find that a gel every 5km works wonders for you.

My best piece of advice is to practise taking energy gels during your long runs. You don’t want to find out how many gels you can take before needing the bathroom on marathon day…

Also, remember that you can take other foods other than energy gels. You can consume energy bars, chews, rice cakes, and even sweets.

What are the best foods to carb load before a marathon?

The best foods to carb load before a marathon include complex carbs, such as rice, pasta, and even homemade pizza. If you’re struggling to eat enough carbs, include simple carbs such as bagels with peanut butter or sweet treats (but don’t overdo it).