How Many Carbs to Eat on Race Day for Peak Performance

December 3, 2025 •

3 min read

Endurance athletes who properly fuel with carbohydrates can perform significantly better during races, a strategy backed by decades of sports nutrition research. Knowing precisely how many carbs to eat on race day is the key to unlocking this performance, preventing fatigue, and avoiding the dreaded 'wall'.

Quick Summary

This guide provides science-backed guidelines for determining your optimal carbohydrate intake, covering pre-race carb loading, morning meals, and hourly consumption during the event. It explains fueling for different race distances and offers practical tips to prevent gastrointestinal issues.

Key Points

Pre-Race Carb Loading: For events over 90 minutes, start carb loading 36-48 hours before the race, aiming for 8–12g of carbs per kg of body weight daily.
Race Morning Meal: Eat 2-4 hours before the race, consuming 1–4g of easily digestible carbs per kg of body weight.
Intra-Race Fueling: Consume 30-60g of carbs per hour for events lasting 1–2.5 hours, increasing to 60-90g/hr for longer races.
Dual-Source Carbs: For higher hourly intakes (60g+), use products with both glucose and fructose to improve absorption and prevent GI issues.
Practice Nutrition Strategy: Test your exact race day fueling plan during long training runs, including the specific gels, chews, or drinks you plan to use.
Train Your Gut: Gradually increase your hourly carb intake during training over several weeks to help your digestive system adapt to race intensity fueling.
Avoid GI Distress: Limit fat, fiber, and protein intake before and during the race, as these can slow digestion and cause stomach cramps.

Why Carbohydrates Are Crucial for Race Day

Carbohydrates are the body's primary and most efficient fuel source for high-intensity and endurance exercise. Stored as glycogen in the muscles and liver, they are essential for sustained effort. For events over 90 minutes, glycogen stores can deplete, causing fatigue or 'hitting the wall.' Consuming carbs before and during the race helps maintain energy levels.

The Three Phases of Race Day Fueling

Effective race day fueling involves three key stages: carb loading before the race, the pre-race meal, and fueling during the event. Strategic planning for each phase is crucial for maximizing energy and minimizing digestive issues.

Phase 1: Carb Loading (2-3 Days Before)

Carb loading is recommended for events lasting 90 minutes or longer and aims to maximize muscle glycogen stores. It typically starts 36-48 hours pre-race, combining increased carb intake with reduced training. A common target is 8–12 grams of carbohydrates per kilogram of body weight daily. For example, a 70kg athlete would aim for 560–840 grams daily. Focus on easily digestible, low-fiber carbs like white pasta, rice, bagels, and potatoes. Reduce fat and protein, and stay well-hydrated.

Phase 2: The Race Morning Meal

The pre-race meal replenishes liver glycogen and should be eaten 2–4 hours before the start to allow digestion. Aim for 1–4 grams of carbs per kilogram of body weight, focusing on low-fiber, low-fat options you've tested in training. Examples include oatmeal, a bagel with jam, or low-fiber cereal with a sports drink.

Phase 3: Fueling During the Race

For events over 60–90 minutes, in-race fueling maintains blood glucose and delays fatigue. The hourly target is 30–60 grams for races up to 2.5 hours and 60–90 grams for longer events. Elite or well-trained athletes in ultra-endurance can tolerate up to 120 grams per hour using dual-source carbs (glucose and fructose) to enhance absorption and reduce GI issues. Start fueling within the first 30–45 minutes and maintain a consistent intake. Practicing your fueling strategy during long training runs helps train your gut to tolerate race-level intake.

Comparison Table: Carb Strategy by Race Distance


Race Distance	Duration	Pre-Race Carb-Loading	Pre-Race Meal (2-4 hrs out)	In-Race Fueling (per hour)
10K	30-70 mins	6g/kg body weight day prior.	1-2g/kg body weight.	Optional (Small amounts if high intensity).
Half Marathon	90+ mins	10-12g/kg body weight days prior.	1-4g/kg body weight.	30-60g carbs.
Marathon	3-5+ hours	8-12g/kg body weight days prior.	2-4g/kg body weight.	60-90g carbs.
Ultra-Endurance	4+ hours	8-12g/kg body weight days prior.	2-4g/kg body weight.	90-120g carbs (with gut training).

The Importance of Practice and Gut Training

Practicing your fueling strategy during training is vital. The gut is adaptable and can be trained to process higher carbohydrate amounts efficiently under race conditions, reducing the risk of GI issues. This 'gut training' involves gradually increasing your carbohydrate intake during long runs. Use the exact products you plan for race day, as tolerance varies.

Common Fueling Mistakes to Avoid

Trying new things on race day: Stick to foods and products tested in training.
Waiting too long to fuel: Start fueling within the first 30-45 minutes of a long race.
Too much fiber or fat: These slow digestion and can cause discomfort. Choose low-fiber, low-fat options.
Underestimating hydration: Proper hydration is essential for digestion and overall performance.

Conclusion: Fueling is the Fourth Discipline

Optimizing race day nutrition is critical for endurance athletes. Determining how many carbs to eat depends on race distance, tolerance, and training. Effective strategies include proper carb-loading, a low-fiber pre-race meal, and consistent in-race fueling with dual-source carbs. Practicing your nutrition plan extensively during training is key to ensuring gut preparedness and maximizing performance on race day.

Optional Outbound Link: To fine-tune your nutrition plan, consider consulting with a qualified sports dietitian.

Frequently Asked Questions

Carb loading is generally not necessary for races lasting less than 90 minutes, like a 10K, as your existing glycogen stores are typically sufficient. A solid, carb-rich breakfast the morning of the race is usually enough.

The best race day breakfast is one you have practiced extensively in training. It should be rich in easily digestible carbohydrates and low in fat and fiber. Examples include oatmeal with a banana, a plain bagel with jam, or white toast with a small amount of honey.

You should start fueling early in a marathon, within the first 30–45 minutes. Do not wait until you feel tired or depleted, as it is much harder to recover at that point.

For races under 2.5 hours, energy gels, drinks, and chews are often preferable for their easy digestibility and quick absorption. While real food can be used, particularly for longer ultra-endurance events, it carries a higher risk of GI upset during high-intensity running.

If you experience stomach issues, slow down your pace and consider backing off your carbohydrate intake for a bit. Ensure you are properly hydrated with electrolytes, as dehydration can contribute to GI distress.

Gut training is an essential component of preparing for an endurance race. It involves gradually increasing your carbohydrate intake during training to teach your digestive system to process fuel efficiently and tolerate race-level fueling without issues.

While gels are a convenient fuel source, relying solely on them can lead to flavor fatigue and GI issues. Combining different fuel types, such as gels, chews, and sports drinks, can make it easier to meet your hourly carbohydrate goals.