Should I carb load before race? Your definitive guide to strategic fueling

December 16, 2025 •

4 min read

Proper carbohydrate loading can improve athletic performance and reduce fatigue by 2-3% for activities longer than 90 minutes. For many athletes, this raises the key question: should I carb load before race? The answer depends on your event's duration and how you strategically approach your pre-race nutrition.

Quick Summary

Carb loading benefits endurance events over 90 minutes by maximizing muscle glycogen stores, delaying fatigue, and improving performance. It involves increasing carbohydrate intake and tapering training in the 1-3 days leading up to a race.

Key Points

Event Duration Matters: Carb loading is most effective for endurance events lasting over 90 minutes, such as marathons and half-marathons.
Timing is Key: Begin increasing your carbohydrate intake 1-3 days before your race, not just with a huge meal the night before.
Focus on Low-Fiber Carbs: Stick to easy-to-digest sources like white rice, pasta, and bananas to prevent GI issues on race day.
Practice During Training: Never try a new carb-loading strategy or food on race day. Practice your fueling plan during your longest training runs.
Hydration is Crucial: Glycogen is stored with water, so remember to increase your fluid intake along with your carbs.
Expect Temporary Weight Gain: The slight increase in scale weight is normal and means your glycogen and water stores are being maximized. Don't panic.

The Science Behind Carb Loading

Carbohydrates are your body's most accessible source of energy during high-intensity and prolonged exercise. Your body stores carbohydrates as glycogen in the liver and muscles. For most people, these glycogen reserves can fuel about 90 to 120 minutes of continuous, high-intensity exercise. When these stores run low, athletes experience a sudden drop in performance, often referred to as "hitting the wall".

Carbohydrate loading is a nutritional strategy to supercompensate, or maximize, these glycogen stores beyond their normal capacity. By increasing carbohydrate intake in the days before a race while simultaneously reducing training volume (tapering), athletes create a glycogen surplus. This extra fuel is stored alongside water, helping to delay fatigue and maintain pace for longer durations during the race. Studies have shown that this strategy can effectively boost performance for events lasting longer than 90 minutes.

Who Should and Shouldn't Carb Load?

Not every athlete needs to implement a full carb-loading strategy. The requirement is directly tied to the duration and intensity of your race.

Carb Loading Is Recommended For:

Marathons and Ultra Events: These races are the classic case for carb loading, as the duration almost guarantees significant glycogen depletion.
Half-Marathons (for most runners): Many runners take longer than 90 minutes to complete a half-marathon, making carb loading a beneficial strategy to avoid fatigue in the final miles.
Long-Distance Cycling or Triathlons: Any endurance event that pushes past the 90-minute mark is a prime candidate for carb loading.

Carb Loading Is Unnecessary For:

5k and 10k Races: For shorter races, a normal balanced diet with a carbohydrate-rich pre-race meal is sufficient. Your body's typical glycogen stores are ample for these distances.
Sprints and High-Intensity Interval Training (HIIT): These are short, high-energy efforts that do not rely on a maximized glycogen tank.

How to Properly Carb Load

Effective carb loading is a science, not just a license to overeat. A modern approach avoids the old "depletion" phase and focuses on a controlled increase in carbohydrates alongside a reduction in training.

A Simple Step-by-Step Plan

Timing (48-72 hours before the race): Start increasing your carb intake 1 to 3 days before your race, depending on the distance. For a marathon, 2-3 days is ideal. This gives your body time to process and store the extra glycogen without feeling bloated right before the start line.
Dosage: Aim for 8-12 grams of carbohydrates per kilogram of body weight per day. For a 70kg (154 lb) runner, this translates to roughly 560-840 grams of carbs daily. This can feel like a lot of food, so spreading it out over several meals and snacks is key.
Food Focus: Prioritize low-fiber, high-glycemic index carbohydrates. This minimizes the risk of gastrointestinal (GI) distress during the race.
Balance Intake: While carbs are the focus, do not completely neglect protein and fat. Maintain a moderate intake to ensure balanced meals, but shift the ratio heavily toward carbohydrates.
Stay Hydrated: Glycogen is stored with water, so increased fluid intake is essential. Aim for consistent hydration throughout the day, and consider adding electrolytes.

Optimal Carb-Loading Food Choices

Choosing the right foods is critical. Focus on easy-to-digest, familiar options to avoid any last-minute surprises on race day.

Good Carb Sources

White pasta and rice
White bread, bagels, English muffins
Oats, low-fiber cereals
Bananas
Potatoes (without the skin)
Pancakes with maple syrup
Pretzels and rice cakes
Sports drinks, fruit juice
Energy gels and chews

Foods to Limit or Avoid

High-Fiber Foods: Whole grains, lentils, beans, and high-fiber vegetables can cause stomach upset.
High-Fat Foods: Fried foods, creamy sauces (like Alfredo), and high-fat dairy can fill you up too quickly and slow digestion.
New Foods: Race week is not the time to experiment. Stick to your tried-and-true training foods.

Carb-Loading for a Marathon vs. a Half Marathon


Feature	Marathon (26.2 miles)	Half Marathon (13.1 miles)
Carb Load Needed?	Yes, for nearly all runners.	Yes, if you expect your finish time to exceed 90 minutes.
Duration of Load	2-3 days prior to the race.	1-2 days prior to the race is often sufficient.
Carb Target (g/kg/day)	10-12g/kg/day.	Often at the lower end of the range, 7-10g/kg/day.
Timing Pre-Race Meal	A large, carb-heavy breakfast 3 hours before start.	A standard, carb-heavy breakfast 2-3 hours before start.
Race-Day Fueling	Essential, with frequent gel/chew intake starting early.	Beneficial, especially for slower runners, to maintain consistent energy.

Conclusion

Carb loading is a proven, science-backed strategy that can significantly benefit endurance athletes in events lasting over 90 minutes. By strategically increasing your carbohydrate intake and reducing your training load in the 1-3 days leading up to the race, you can top off your glycogen stores, delay fatigue, and improve your performance. It is important to practice your carb-loading routine during training to discover what foods and timing work best for your body. For shorter races, such as a 5k, a standard, well-balanced diet is all you need. Ultimately, effective fueling is a critical component of your race preparation, ensuring you arrive at the start line ready to perform at your best. For more on effective fueling strategies, including timing and food choices, consult reputable sports nutrition resources such as Precision Hydration.

Frequently Asked Questions

No, carb loading is generally not necessary for races shorter than 90 minutes. Your body's normal glycogen stores are sufficient, and a regular, balanced diet is all you need.

A moderate, high-carbohydrate, low-fiber, and low-fat dinner is ideal. Avoid a massive meal that could disrupt sleep or digestion. Examples include white pasta with a simple tomato sauce, baked potatoes, or white rice with a lean protein source.

Yes, a temporary weight gain of 2-4 pounds is common and expected. This is because every gram of stored glycogen is bound with water. This extra water is beneficial for hydration during the race.

Avoid high-fiber foods like whole grains and legumes, high-fat foods like fried items and creamy sauces, and new, unfamiliar foods. These can all lead to gastrointestinal distress.

Yes. For a half marathon, you typically only need 1-2 days of increased carbs, while a full marathon requires 2-3 days. The daily carbohydrate target per kilogram of body weight is also often higher for a marathon.

The old carb-loading method of first depleting glycogen stores with a low-carb diet is now considered outdated and unnecessary. It can lead to fatigue and stress. The modern method focuses on simply increasing carb intake while tapering training.

Yes, drinking carbs can be a very effective way to increase your intake without feeling too full. Sports drinks and fruit juice can supplement solid food, just be mindful of high sugar intake too close to bedtime.