Carb Loading for a Half Marathon: Do You Need It?

If you’re feeling a little nervous about race-day nutrition, you’re not alone, 21.1 km is a big deal. A half marathon sits right in that grey zone where fuelling can meaningfully influence performance, but it doesn’t require the same aggressive strategies used for a full marathon. The goal is simple, start the race with well-stocked glycogen stores so you can hold pace, especially in the final kilometres when fatigue creeps in. The good news? Carb loading for a half marathon is far more straightforward than many runners expect, and overdoing it can sometimes cause more harm than good, think bloating, GI discomfort and sluggishness.

For most recreational runners, a full 2-3-day carb load isn’t necessary before a half marathon. Instead, aiming to meet your usual daily carbohydrate needs, typically around 5-7g/kg/day for most runners, during the 24 hours leading into race day is enough to top up glycogen stores for a 2-hour-plus effort¹.

The Science: Half Marathon vs. Full Marathon Fuelling

• Duration matters for glycogen needs → Elevated pre‑race muscle glycogen can significantly delay fatigue in events lasting longer than 90 minutes by postponing glycogen depletion, the main trigger for exhaustion³.
  

• Half marathons are generally shorter → Most runners complete a half marathon in 90-150 minutes, meaning the risk of fully depleting glycogen is lower than in a full marathon, which often lasts 3-4 hours²,³.
  

• Carb loading provides a safety net → Events over 90 minutes rely heavily on carbohydrate metabolism. Even half marathon runners, particularly first‑timers or those on their feet for 2+ hours, benefit from modest carbohydrate loading to ensure glycogen stores are topped up throughout the race¹,⁴.
  

• Carbs improve performance → Systematic reviews show consuming carbohydrates before and during endurance events helps maintain pace, supports energy levels and boosts exercise capacity².
  

• Practical strategy for half marathoners → Focus on familiar, low-fibre, easily digestible carbohydrates in the 1-3 days before race day. This can include white rice, pasta, bread, pikelets or carbohydrate-rich smoothies, which help top up glycogen without causing gastrointestinal issues¹,⁴. 

• Benefit for first-time runners→ For runners new to half marathons, even a modest carb-loading approach provides an energetic safety buffer, helping reduce fatigue, maintain mental focus and finish strong²,³

How to Carb Load for a Half Marathon (The 24-Hour Plan)

• What carb loading for a half marathon really means → Unlike full marathons, which often use a 2-3‑day carbohydrate loading protocol, half marathon runners generally only need to consciously increase carbohydrate intake in the day or two before the race. This is usually enough to top up muscle and liver glycogen without overeating. Well-stocked glycogen stores help maintain endurance and delay fatigue¹⁻⁴.
  

• Aim for high‑carb, low‑fibre foods → Choose easily digested carbohydrates such as white rice, pasta, bagels, low‑fibre bread, potatoes, pretzels, bananas and fruit juice. These provide rapid carbohydrate without the bloating high‑fibre foods can cause, which is important within 24 hours of racing¹.
  

• Spread carbs across the day → Rather than one huge meal, distribute carbohydrate across 3-4 meals and snacks to help digestion and maximise glycogen synthesis. Focus on your usual daily carbohydrate intake, for most half marathon runners this sits around 5-7g/kg/day, with higher intakes only needed if training volume is very high¹,³.
  

• Hydration supports glycogen storage → Adequate fluid intake is crucial; glycogen binds water in muscle, dehydration can limit glycogen storage and performance¹.
  

• Limit fat and fibre → Fat and fibre slow digestion and can increase GI discomfort, reduce these in the 1-2 days before¹.

• Pre‑race morning boost → Eat a small, easy carbohydrate breakfast 2-4 hours before start, for example a bagel with nut butter OR a banana with honey to top off liver glycogen and maintain blood glucose through the race¹.

Liquid Carbs: The Secret for Nervous Runners

• Pre-race nerves affect digestion → Race-day anxiety or “butterflies” can slow gastric emptying and reduce appetite, making large or fibre-dense carbohydrate meals harder to tolerate, especially in the final 24 hours before a race¹.
  

• Liquid carbs are often better tolerated → Carbohydrate drinks, juices, or smoothies require less mechanical digestion and are often better tolerated than solid foods, allowing energy to be absorbed more easily without adding to feelings of fullness or gastrointestinal discomfort²,³.
  

• Liquid carbs as a backup → For nervous runners or those prone to GI issues, liquid carbohydrates can be used strategically if solid high-carb meals feel unappealing or intolerable the day before or on race morning. They offer a simple, reliable way to top up glycogen and maintain blood glucose while minimising gastrointestinal distress¹,²,⁴.
  

Learn more → Explore options and strategies here Carbs & Drink Mixes.

What to Eat the Night Before 21.1km

The evening before your half marathon is about topping up glycogen while keeping your stomach comfortable. Stick to familiar, easy-to-digest foods, this is not the time to try spicy, fatty, or heavy meals. Focus on simple starches such as white rice, potatoes or white breads paired with a moderate portion of protein like chicken, fish, or tofu and a small amount of fats.

Some practical meal ideas include:

• Pizza with tomato base veggies and cheese

• White rice with lightly cooked vegetables and grilled fish

• Baked potato with a small portion of lean protein

Keep portions moderate to avoid feeling overly full, and stay hydrated alongside your meal. By sticking to foods you’ve tested during training, you’ll maximise glycogen storage, reduce the risk of GI discomfort and set yourself up for a strong half marathon performance the next day.

Common Half Marathon Fuelling Myths

• Myth: You must overeat → Carb loading for a half marathon is not about eating until stuffed. Overeating can cause bloating, GI distress and poor sleep.

• Focus on quality and timing → Strategic intake of moderate portions of low-fibre, easily digestible carbohydrates over the day before and morning of the race is more effective than simply increasing quantity.

• Familiar foods work best → Stick to foods you’ve tested during training to avoid gastrointestinal issues on race day.

• Goal of carb loading → Maximise muscle and liver glycogen to maintain energy, sustain pace and delay fatigue without discomfort.

• Practical takeaway → Success comes from smart carb choices and timing, not sheer volume of food

Conclusion: Strategy Beats Luck on Race Day

Even though a half marathon is shorter than a full marathon, carb loading for a half marathon remains a vital part of preparation, especially for first-time runners. In the day or two before the race, stick with familiar low-fibre meals, and smart pre-race fuelling to give your muscles and liver the energy they need to sustain pace and delay fatigue. Planning your nutrition isn’t just about food, it’s about confidence, control and setting yourself up for a strong performance. Don’t leave your race day to chance. Shop our Half Marathon Fuelling Bundle’s to ensure you have exactly what you need from the first k until the finish line.

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

References

1. Kerksick CM, Arent S, Schoenfeld BJ, Stout JR, Campbell B, Wilborn CD, Taylor L, Kalman D, Smith-Ryan AE, Kreider RB, Willoughby D, Arciero PJ, VanDusseldorp TA, Ormsbee MJ, Wildman R, Greenwood M, Ziegenfuss TN, Aragon AA, Antonio J. International society of sports nutrition position stand: nutrient timing. J Int Soc Sports Nutr. 2017 Aug 29;14:33. doi: 10.1186/s12970-017-0189-4. PMID: 28919842; PMCID: PMC5596471.

2. Stellingwerff T, Cox GR. Systematic review: Carbohydrate supplementation on exercise performance or capacity of varying durations. Appl Physiol Nutr Metab. 2014 Sep;39(9):998-1011. doi: 10.1139/apnm-2014-0027. Epub 2014 Mar 25. PMID: 24951297.

3. Hawley JA, Schabort EJ, Noakes TD, Dennis SC. Carbohydrate-loading and exercise performance. An update. Sports Med. 1997 Aug;24(2):73-81. doi: 10.2165/00007256-199724020-00001. PMID: 9291549.

4. Solem K, Clauss M, Jensen J. Glycogen supercompensation in skeletal muscle after cycling or running followed by a high carbohydrate intake the following days: a systematic review and meta‑analysis. Front Physiol. 2025 Aug 18;16:1620943. doi:10.3389/fphys.2025.1620943.

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.