Carb Loading Before a Marathon: Timing and Strategy

Key Takeaways

Start early→ Begin carb loading 2-3 days before the marathon, not just the night before, to maximise glycogen stores.
Choose the right carbs→ Focus on complex carbohydrates a few days out (pasta, rice, oats) and switch to low-fibre, easily digestible options (white rice, bread, honey, juice) in the final 24 hours.
Taper training→ Reduce training volume while increasing carbohydrate intake to allow muscles to store glycogen efficiently.
Hydration and timing matter→ Sip electrolyte fluids in the days leading into the race. On race morning, eat your main meal 2-3 hours before the start to support digestion and reduce GI discomfort. Take a simple carbohydrate source (gel, chew, waffle, or drink mix) 20-30 minutes before the race.
Fuel during the race→ Use energy gels or carbohydrate drinks to maintain blood glucose and delay fatigue, complementing pre-race carb loading strategies

Carb Loading Before a Marathon: Timing and Strategy

Race week is where months of training meet smart nutrition, and carbohydrate becomes the star of the show. While fitness sets your potential, marathon performance is primarily limited by glycogen availability rather than training alone¹,².

Carb loading is the strategy of increasing carbohydrate intake (6-12g/ kg of body weight) 2-3 days before a marathon to maximise muscle glycogen. This process ensures the body has enough fuel to maintain pace and delay fatigue during the race.

Muscle glycogen is the body’s most efficient fuel for sustaining marathon pace, particularly in the final stages of the race. When glycogen stores fall too low, fatigue rises, pace drops, and the classic “hitting the wall” becomes far more likely¹,². Research consistently shows that higher pre-race glycogen levels improve endurance performance and delay fatigue¹,².

What is Carb Loading and Why Does It Matter?

Carb loading increases glycogen stores in our muscles and liver prior to endurance events¹,³.
Muscle glycogen fuels working muscles. Liver glycogen maintains blood glucose for the brain and muscles⁴.
Glycogen depletion leads to “hitting the wall”, sudden fatigue, slowed pace, and reduced mental focus¹.
This can typically occur around the 30-35 km mark in a marathon if stores are low¹,³.
Strategic carbohydrate intake 2-3 days before racing maximises glycogen and delays fatigue³.
Combining pre-race carb loading with energy gels during the race can maintain blood glucose and support ongoing performance⁴.
Research shows higher pre-race glycogen improves endurance, delays exhaustion, and enhances race-day performance⁴.

When to Start: The 48-Hour Carb Loading Timeline

Start carb loading around 2-3 days before the marathon, not just the night before, to maximise glycogen stores, this helps loading carbs¹,²,⁵.
Gradually increase carbohydrate intake to 6-12g/kg of body weight per day, focusing on white pasta, rice, fruits, white bread, starchy vegetables and honey/maple syrup¹,⁴,⁷.
Reduce training volume (tapering) during this period, allowing the body to store glycogen efficiently without using it up¹,²,⁶.
Prioritise easily digestible (low fibre) carbohydrates in the final 24 hours to avoid gastrointestinal discomfort and ensure glycogen loading is not compromised⁴.
Hydration is key, glycogen storage pulls water into muscles, so maintain adequate fluid intake alongside increased carbohydrates¹,².
Small pre-race carbohydrate snacks or drinks on race morning can top off liver glycogen without overloading the stomach⁴,⁶.

What to Eat: Choosing the Right Carbohydrates

In the final 24 hours before a marathon, carbohydrate type matters as much as quantity¹,².
Complex carbs (whole grains, beans, vegetables) are nutritious but high in fibre which may cause GI distress on race day, avoid these in the 1-2 days before your marathon¹,².
As you get closer to race day the focus should be on low-fibre, easily digestible carbs to maximise glycogen without upsetting the stomach¹⁻³.
Ideal foods→ white rice, white bread, pretzels or liquid carbs like juice or carbohydrate-rich smoothies¹,²,³,⁵.
Goal→ maximise glycogen stores while minimising fibre and fat, which slow digestion¹,²,⁴.
Carbohydrate target→ 6-12g/ kg of body weight over the 2-3 days before the race¹,²,⁴,⁵.
Combine solid and liquid carbs to help increase carbohydrate intake³,⁵.
Stick to familiar foods that have been well-tolerated during training to avoid GI issues¹,².

The Day Before the Marathon: Meal Examples

Breakfast→ Pancakes with maple syrup + small banana (easy-to-digest carbs)¹,².
Lunch→ Grilled chicken with white rice + small portion of cooked vegetables (protein + low fibre)¹,².
Dinner→ Plain pasta with bolognaise sauce with cheese/chicken/beef/tofu¹,².
Snacks→ Rice cakes, bakery items, pikelets, pretzels or carbohydrate-rich smoothies¹⁻³.
Tip→ Choose familiar foods tested in training to reduce risk of digestive issues¹,².

Common Mistakes to Avoid During a Marathon Carb Load

Focus on complex carbohydrates (pasta, rice, oats) in the 2-3 days before the marathon to maximise glycogen stores¹,²,⁵.
Switch to low-fibre, easily digestible carbohydrates in the final 24 hours to reduce gastrointestinal discomfort. Examples include white rice, white bread, pikelets, honey or maple syrup³,⁴
Include liquid carbohydrates if appetite is low or for easy digestion; options include sports drinks, smoothies, or juice¹,⁶
Avoid high-fibre or high-fat foods right before the race, as these slow digestion and may increase GI upset⁴,⁵.
Keep fluids up. You need water during carb loading to help your body store glycogen effectively.
Gender-specific considerations→ some evidence suggests women may oxidise slightly more fat and less carbohydrate during endurance exercise, but carbohydrate loading is still effective for both sexes⁷.
Timing of meals→ aim to finish the last large carbohydrate meal 3-4 hours before race start to allow digestion and prevent discomfort¹,².

Conclusion: Fuelling Your Way to the Finish Line

A successful marathon is built on the plate as much as the pavement. Proper carbohydrate strategies starting 2-3 days before the race, tapering training, and choosing the right carbs ensure your muscles and liver are stocked with glycogen to delay fatigue and maintain pace. Consistency in both nutrition and training is key; last-minute fixes rarely work. Planning ahead allows your body to perform at its best and reduces the risk of hitting the wall.

Ready to fuel your best race? Recommended bundles to take the guesswork out of your marathon prep are Skratch lab Energy Bar Discovery Bundle , Clif Bar Top Energy Bar Flavours Bundle OR our Full Marathon Kit.

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

References

Burke LM et al. Carbohydrates for training and competition. J Sports Sci, 2011.
Hawley JA et al. Effect of carbohydrate loading on muscle glycogen and endurance performance. Sports Med, 1997.
Hawley JA, Burke LM. Effect of carbohydrate loading on muscle glycogen and endurance performance. Sports Med, 1997;24:73–81.
Cermak NM, van Loon LJ. The use of carbohydrates during exercise as an ergogenic aid. Sports Med, 2013;43:1139–1155.
Bosch AN. Carbohydrate loading. In: Mooren FC, Westerterp KR, editors. Encyclopedia of Exercise Medicine in Health and Disease. Berlin: Springer; 2012. p. 144-146.
Dos Santos LC, de Moura Costa C, de Moura RC, Silvino VO, Dos Santos MAP, Brandão ACAS. Effects of carbohydrate supplementation on the performance of endurance athletes: a systematic review. Clin Nutr ESPEN. 2025;68:198‑205.
De Heer EW, et al. Gender differences in carbohydrate metabolism and carbohydrate loading. J Int Soc Sports Nutr. 2006;3:28

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.