How to Carb Load for a Marathon

Want to avoid hitting the wall on race day? Carb loading is a proven strategy to top up glycogen stores in your muscles and liver, giving you the energy to maintain pace and delay fatigue during long runs or marathon races. Aid Station’s dietitian, Ash, walks you through how to carb load efficiently, covering the best timing, methods, foods, and common mistakes to help you stay race-ready and feel lighter on your feet.

Step-by-Step Guide on How Do You Carb Load for a Marathon

Carb loading can be a game-changer for endurance events lasting over 90 minutes, helping you maintain pace, delay fatigue and avoid hitting the wall. Here’s a practical guide on how to carb load effectively in the days leading up to your marathon.

1. Plan your timing (1-3 days before race)
 Start carb loading 1-3 days out, depending on your tolerance. This short, focused phase allows glycogen stores to peak without overloading your stomach (1,2).

2. Reduce training intensity
Taper your runs and reduce training volume to conserve energy. Lower intensity allows your muscles to store more glycogen from the extra carbs you’re consuming (3).

3. Boost daily carbohydrate intake
 Aim for 6-12 g of carbohydrate per kilogram of bodyweight per day. In male endurance athletes, this can increase glycogen storage by up to 40% and improve performance by 2-3% in long events, while female athletes may experience smaller increases depending on energy intake and hormonal factors (4,5,6).

4. Focus on low-fibre, easy-to-digest foods
Stick to familiar, simple carbs like rice, white bread, bananas, potato, yoghurt, creamed rice, juice and even ice-cream. Avoid high-fibre foods that can cause bloating or digestive discomfort on race day (2,7).

5. Stay hydrated
Drink plenty of water with an electrolyte drink mix to support glycogen storage and prevent dehydration, especially in hot Australian conditions 9.

6. Plan your race-day breakfast
Have a familiar, carb-focused breakfast 2-3 hours before the start. Keep it simple, think bagel with nutella, toast with honey or pikelets with maple syrup 2,9.

7. Practice during training
Test your carb-loading strategy the day before long runs to ensure it works for you and avoids stomach issues on race day 8.

By following these steps, you can top up glycogen stores efficiently and give yourself the energy edge to perform your best.

What’s Carb Loading and Why Carbohydrate Loading Matters for a Marathon

Carbohydrate loading for a marathon is the process of increasing glycogen stores in your muscles and liver in the days leading up to a long-distance event (1,2). These glycogen reserves act as your body’s main energy source during endurance exercise, helping you maintain pace and delay fatigue over the course of 42.2 km (2,3). By strategically topping up these energy stores, runners can enhance performance, reduce the risk of “hitting the wall,” and feel more fuelled throughout the race (1,3,4). While carb loading can make a noticeable difference for marathon performance, the exact timing, amounts, and types of carbohydrates used are best explored in detail in a dedicated guide on how to carb load efficiently for race day (1,5).

When to Start Carb Loading Before a Marathon

(Timing is key when planning your carb load for a marathon. Most athletes benefit from starting 1-3 days before race day. During this period, training intensity should taper, allowing your muscles to rest while maximizing glycogen storage. This combination of tapering and targeted carbohydrate intake helps ensure your energy reserves are full on race morning, supporting pace maintenance and delaying fatigue. Pairing carb loading with adequate recovery strategies, like proper sleep and hydration, enhances your body’s ability to store and use glycogen efficiently (2,4,9).

How to Carb Loading Effectively for Endurance and Energy

Knowing how to carb loading is key to fuelling your marathon efficiently. For males, aim for 8-12 g of carbohydrate per kilogram of body weight per day, while females may benefit from slightly lower targets of 5-8 g/kg/day, ideally timed during the follicular phase (2,7,9). For example, a 60kg female would aim for 300-480 g of carbs daily, while a 60kg male would target 480-720 g. Focus on low-fibre, easy-to-digest foods such as pasta, rice, bread, potatoes, bananas, and fruit juices to top up glycogen without digestive discomfort  (2,7,9).

Test this strategy during training to ensure your stomach tolerates the portions and types of carbs, so race day feels smooth and energised.

 

Best Foods to Eat to Carb Load for a Marathon

When preparing for a marathon, choosing the right carbs is key. Focus on low-fibre, high-GI foods that are easy to digest and maximise glycogen stores without upsetting your stomach. Staples like white rice, potatoes, pikelets and bagels provide a steady source of energy, while fruit such as ripe bananas, grapes, and berries adds quick, natural sugars. During long training sessions or race day, energy gels and carb/electrolyte drink mixes can help top up carbs and support hydration. Sticking to familiar, tested foods ensures your carb-loading strategy is both effective and comfortable on race day.

What Foods to Avoid When Carb Loading for a Marathon

When carb loading, some foods can cause digestive discomfort and slow you down. Avoid high-fibre foods, heavy fats, spicy meals, and unfamiliar foods, which can lead to bloating or stomach upset on race day (1,2,9). Instead, choose low-fibre, easy-to-digest alternatives such as white rice instead of brown rice, bagels instead of multigrain bread, peeled potatoes and familiar fruits like bananas. Keeping pre-race meals simple and tested ensures your glycogen stores are topped up without any unpleasant surprises, helping you feel light, fuelled, and ready for the marathon.

 How Do I Carb Load Without Overeating or Feeling Bloated

Spread carbohydrate intake across 4-6 smaller meals each day in the 2-3 days before your marathon. Hydration is key, as water helps with glycogen storage, and including a small amount of sodium in your meals or sports drinks can improve glycogen uptake (1-4).

3-Day Carb Load Marathon Meal Plan Example

 

Race Day Nutrition: How to Carb Load Before Running a Marathon

Timing and strategy on race day can make or break your marathon performance. Aim to eat a carbohydrate-rich meal 3-4 hours before the start, targeting 1-4 g of carbs per kilogram of bodyweight depending on your tolerance and race length, (2,4,9). Choose low-fibre, easily digestible foods like white bread, bagels, english muffins or pikelets to avoid stomach discomfort (1,3). Hydration is equally important, sip water with electrolyte in the lead-up 1,9. For those needing extra fuel closer to the start, small, familiar snacks like Maurten or Precision gels or chews can be useful (2,9). Practicing this routine during training ensures your stomach and energy levels stay race-ready on the big day (2,4).

 

Common Carb Loading Mistakes Marathon Runners Should Avoid

Carb loading can make a big difference on race day, but only if done right. Common mistakes include:

• Starting too late → Begin 1-3 days before the marathon to top up glycogen effectively.
  

• Eating too much fibre → High-fibre foods can cause bloating and stomach upset; stick to low-fibre, easily digestible carbs.
  

• Skipping hydration → Water and electrolytes help glycogen storage and prevent dehydration.
  

• Overdoing portion sizes → Excess food can lead to discomfort and sluggishness.

Remember: test your carb-loading plan during training, not on race day. Practising what works for you helps you feel fuelled, light, and confident when it counts.

 

 Expert Carb Loading Advice from Aid Station’s Sports Dietitian

Ash Miller, Aid Station’s dietitian, emphasizes the value of planning and practising your nutrition: “Don’t get caught up in race-week hype or complicated carb intake rules. Stick to what you know works, keep it simple, familiar, and gut-friendly.” Following a tested approach ensures your body feels fuelled and comfortable on marathon day.

Fuel up with Aid Station’s same-day dispatch on trusted endurance nutrition brands.

 

FAQs: How to Carb Load for a Marathon and Common Questions

How many days before a marathon should you start carb loading?

For most runners, start carb loading 1-3 days before race day. This gives your muscles and liver time to maximise glycogen stores without overloading your stomach. For a Sunday marathon, begin Thursday, Friday or Saturday, reducing training intensity while increasing carbohydrate intake to top up energy reserves (1,2,9).

Can you carb load the night before a marathon?

A pre-race dinner can include some additional carbohydrates, but don’t rely solely on one meal to fuel the day. Focus on a moderate, familiar portion of low-fibre carbs, like rice, pretzels or pikelets. The main glycogen boost comes from the 1-3 days leading up to race day 1-3.

What’s the difference between tapering and carb loading?

Tapering reduces training intensity and volume to allow recovery, while carb loading increases glycogen stores. They work together: tapering limits energy use, so your carbohydrate intake more effectively fills muscles and liver stores (1,3,4).

Do shorter races need carb loading too?

Races under 90 minutes generally don’t require carb loading. Normal daily carbohydrate intake is usually sufficient for shorter events such as 5 km, 10 km, or HYROX-style competitions (1,4).

How do you know if you’ve carb loaded properly?

Signs of effective carb loading include feeling fuelled but not bloated, having steady energy during long runs, and maintaining pace with delayed fatigue. Practising your plan during training helps ensure it works on race day 1-3.

 

Ash Miller
Dietitian and Nutritionist (Masters)
Bachelor of Physical and Health Education
Instagram: @ashthomo_nutrition

 

References

1.  Bosch AN. Carbohydrate loading. In: Mooren FC, Westerterp KR, editors. Encyclopedia of Exercise Medicine in Health and Disease. Berlin: Springer; 2012. p. 144-146.

2. Patterson A. Carb Loading for Success: What You Need to Know [Internet]. Melbourne: Sports Dietitians Australia; 2017 Jun 27 [cited 2025 Nov 11]. Available from: https://www.sportsdietitians.com.au/sda-blog/carb-loading-success/#:~:text=How%20much%20carbohydrate%20do%20I,day%20for%20a%2060kg%20athlete

3. Hargreaves M, Spriet LL. Muscle glycogen stores and fatigue. J Physiol. 2013;591(18):4405‑4413.

4. Kerksick, C. M., Arent, S., Schoenfeld, B. J., Stout, J. R., Campbell, B., Wilborn, C. D., … Antonio, J. (2017). International society of sports nutrition position stand: nutrient timing. Journal of the International Society of Sports Nutrition, 14(1). https://doi.org/10.1186/s12970-017-0189-4

5. Tarnopolsky MA, Zawada C, Richmond LB, Carter S, Shearer J, Graham T, Phillips SM. Gender differences in carbohydrate loading are related to energy intake. J Appl Physiol (1985). 2001 Jul;91(1):225-30. doi: 10.1152/jappl.2001.91.1.225. PMID: 11408434. 7615443.10.1249/MSS.0000000000002850. Epub 2021 Dec 30. PMID: 34974499.

6. Wismann J, Willoughby D. Gender differences in carbohydrate metabolism and carbohydrate loading. J Int Soc Sports Nutr. 2006 Jun 5;3(1):28-34. doi: 10.1186/1550-2783-3-1-28. PMID: 18500960; PMCID: PMC2129154.

7. Sims ST, Kerksick CM, Smith-Ryan AE, Janse de Jonge XAK, Hirsch KR, Arent SM, Hewlings SJ, Kleiner SM, Bustillo E, Tartar JL, Starratt VG, Kreider RB, Greenwalt C, Rentería LI, Ormsbee MJ, VanDusseldorp TA, Campbell BI, Kalman DS, Antonio J. International society of sports nutrition position stand: nutritional concerns of the female athlete. J Int Soc Sports Nutr. 2023 Dec;20(1):2204066. doi:  10.1080/15502783.2023.2204066. PMID: 37221858; PMCID: PMC10210857.

8. Menzies C, Wood M, Thomas J, et al. Frequent carbohydrate ingestion reduces muscle glycogen depletion and postpones fatigue relative to a single bolus. Int J Sport Nutr Exerc Metab. 2020;30(3):203‑209.

9. Australian Institute of Sport. Carbohydrate Loading Factsheet [Internet]. Canberra: AIS; 2020 [cited 2025 Nov 11]. Available from: https://www.ausport.gov.au/__data/assets/pdf_file/0007/123456/Carbohydrate_Loading_Factsheet.pdf

 

Disclaimer:

The content in this blog is for general information only and is not a substitute for professional medical advice, diagnosis, or treatment. Always speak with your doctor or allied health team before changing your diet, exercise, or taking supplements, especially if you have a health condition or take medication. Please use this information as a guide only. Aid Station doesn't take responsibility for individual outcomes.