What is Carb Loading? Carbohydrate Loading Explained

Forget the “pasta party.” Smart carb loading isn’t about eating more; it’s about fueling right. The wrong approach can leave you bloated, tired, and slower on race day. Learn the science-backed strategy that actually boosts endurance performance.

Carbohydrate loading, or “carb loading,” is a well-established fueling strategy designed to maximise the body’s glycogen stores, the primary source of energy during endurance exercise (1) . By increasing carbohydrate intake in the days leading up to an event, athletes can boost their energy reserves, delay fatigue and enhance performance in competitions lasting longer than 90 minutes (2,3). This simple yet powerful approach helps athletes fuel effectively, recover more efficiently and perform at their best when it matters most (2,3,4).

What does Carb Loading Mean in Sports Nutrition? 

You’ve trained hard, now it’s time to fuel smart. In sports nutrition, carb loading means deliberately eating more carbohydrates than usual in the days before a big endurance event. Unlike your everyday carb intake, which fuels training and recovery, carb loading is a short-term strategy to “fill the tank”, maximising glycogen stores in your muscles and liver so you’ve got energy that lasts on race day.  Daily carbs = maintenance, carb loading = performance prep.

How does Carbohydrate Loading Work in the Body?

When you eat carbohydrates, your body converts them into glucose, which is stored in the muscles and liver as glycogen, the main fuel for endurance exercise. Carb loading boosts these glycogen stores beyond normal levels, giving athletes a larger energy reserve to delay fatigue and maintain performance during long events (5).

What does a Carb Do in the Body?  

For athletes, carbohydrates are the foundation of endurance, recovery, and sustained performance. Here’s how they work in your favour:

• Fuel exercise→ Carbohydrates are broken down into glucose, which muscles use as their main energy source during training and competition (6).

• Supports recovery→ After exercise, carbohydrates help replenish depleted glycogen stores, speeding up recovery and preparing the body for the next session (7,8).

• Prevents fatigue→ Adequate carbohydrate intake delays “hitting the wall” by keeping blood glucose levels stable and reducing early onset of tiredness during long events  (6,9,10).

 

What are Carbohydrates and Why are They Important for Athletes?

Not all carbohydrates are created equal. They're generally grouped into two types, and each serve a different purpose in fuelling performance:

• Simple carbs→ Quick-digesting sugars that provide rapid energy. Examples include pikelets, maple syrup or sports gels.
  

• Complex carbs→ Slower-digesting starches that provide sustained energy. Examples include oats, rice, pasta and whole-grain bread.

 

Glycogen Loading for Marathons and Endurance Sports

Glycogen loading can be useful for marathons and long endurance events, as muscles rely on glycogen for energy. During prolonged exercise, low glycogen can cause fatigue, reduced power or a sharp decline in performance. Increasing carbohydrate intake in the days before a race maximises glycogen stores, which may help athletes maintain pace and delay fatigue. 

 

When Should Athletes Consider Carb Loading?  

Carb loading is most useful for endurance events lasting longer than 90 minutes or for multi-day competitions, where sustaining energy and delaying fatigue is critical. Research shows that men can increase glycogen storage by up to 40% through carb loading, which can improve performance by 2–3% in long events (2,3,11,12). To achieve this, athletes typically consume 5–12 grams of carbohydrate per kilogram of bodyweight in the 1–3 days leading up to competition (2,3,4). This extra energy reserve helps athletes maintain pace, delay fatigue, and avoid “hitting the wall” during demanding endurance exercise (1).

 

How to Approach Carb Loading Safely 

Timing is everything when it comes to fuelling, and carb loading isn’t necessary for every workout. It's most useful for endurance events lasting longer than 90 minutes or multi-day competitions, where maintaining energy and delaying fatigue is critical.

Want to make sure your carb loading actually works for you? Carb loading can be effective, but individual factors like sex, hormonal cycle, and calorie intake affect results. Females may benefit from slightly lower targets (5-8 g/kg/day) and timing carb loading during the follicular phase, while males generally follow standard protocols of 8-12 g/kg/day (2,3,4,13,14). Focus on carb loading 1-3 days before an event, adjusting for personal tolerance to maximise glycogen stores and avoid digestive issues (3,4,15).

Foods Athletes Often Use During Carb Loading  

During carb loading, athletes typically focus on high-carbohydrate, easily digestible foods to maximise glycogen stores without causing digestive discomfort. Common categories include:

• Grains and starches→ pasta, rice, bread and cereals
  

• Fruits→ bananas, grapes, berries, and fruit juices
  

• Vegetables→ starchy options like potatoes, sweet potatoes and corn
  

• Dairy and alternatives→ milk, yogurt, and plant-based options
  

• Sports nutrition→ Hydration drink mixes

Focusing on these familiar, easily digestible carbs helps top up your glycogen stores efficiently, keeping you fuelled and race-ready.

 

Common Mistakes to Avoid in Carb Loading

Carb loading can backfire if it’s not done strategically. Overeating, adding too much fibre, or experimenting with new foods can lead to bloating and discomfort on race day. Women may also need to adjust portions and timing based on hormonal differences.

Stick to familiar, easy-to-digest carbohydrates and aim for balance; enough to top up glycogen without feeling heavy.

A food-first approach is best in the days before your race. Natural, whole-food bars such as Hammer Nutrition Apple Oatmeal Bars, I Am Grounded SUPR Bars, and Blue Dinosaur Energy Bars can help bridge the gap if you’re struggling to meet your carb goals through meals alone.

When real food isn’t enough, drinks like Tailwind Endurance Fuel or Maurten 160/320 can boost your carb intake while supporting hydration. They’re gentle on the stomach and help keep your energy steady from start to finish.

 

Carb Loading vs Normal Diet: Key Differences Explained  

Carb loading differs from everyday eating because it focuses on maximising glycogen stores for endurance performance, while a normal diet maintains general energy and health.

 

Is Carb Loading Only for Marathon Runners?

No, carb loading isn’t just for marathon runners. Any athlete competing in endurance events lasting longer than 90 minutes, such as triathlons, long-distance cycling, rowing or ultra-distance races can benefit.

 

How Many Days Before a Race Should You Start Carb Loading? 

You can start carb loading 1–3 days before an endurance event.

Can Carb Loading Improve Short-Distance Performance?  

Carb loading doesn’t help much for short events under 90 minutes, like sprinting, HYROX or middle-distance races. These rely on quick energy stores in the muscles, so normal carb intake is usually enough.

 

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

 

References

1. 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

2. 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.

3. Burke LM, Hawley JA.Carbohydrate and exercise.Curr Opin Clin Nutr Metab Care21999515520

4. 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.

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

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

7. Gonzalez JT, Wallis GA. Carb‑conscious: the role of carbohydrate intake in recovery from exercise. Curr Opin Clin Nutr Metab Care. 2021;24(4):364‑371.

8. Craven J, Desbrow B, Sabapathy S, McCartney D, Irwin C, et al. The Effect of Consuming Carbohydrate With and Without Protein on the Rate of Muscle Glycogen Re‑synthesis During Short‑Term Post‑exercise Recovery: a Systematic Review and Meta‑analysis. Sports Med Open. 2021;7:9.

9. Santos A, Hamidvand A, Koozehchian SK, Ghazzagh R, Berjisian E, Podlogar T. Nutritional Strategies to Improve Post‑exercise Recovery and Subsequent Exercise Performance. Sports Med. 2025.

10. 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.

11. Tarnopolsky MA, Atkinson SA, Phillips SM, MacDougall JD.Carbohydrate loading and metabolism during exercise in men and women.J Appl Physiol78199513601368

12. 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.

13. Walker JL, Heigenhauser GJ, Hultman E, Spriet LL.Dietary carbohydrate, muscle glycogen content, and endurance performance in well-trained women.J Appl Physiol88200021512158

14. 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

15. Hackney AC. Hormonal influence on exercise performance in females. Sports Med. 2020;50:1027‑1039.

 

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.