How soon before a race should I carb load?

November 30, 2025 •

4 min read

Sports dietitians recommend that athletes begin carb loading in the 24 to 48 hours leading up to an endurance race. This critical window focuses on increasing carbohydrate intake to maximize your body's glycogen stores, which serve as a primary fuel source during high-intensity, prolonged exercise. A properly executed carb load can help you avoid fatigue and hit your performance goals on race day.

Quick Summary

Maximize your race performance by strategically increasing carbohydrate intake 1-3 days before an endurance event. Focus on easy-to-digest, high-carb foods while tapering training to fully stock your glycogen fuel tank. This guide details optimal timing, food choices, and common mistakes to avoid for a powerful race.

Key Points

Start 1 to 3 days before the race: The modern approach to carb loading begins 24 to 72 hours before the event, eliminating the need for a glycogen depletion phase.
Aim for 8-12g of carbs per kg body weight: Your target intake depends on your body weight and the race duration, with longer events requiring the higher end of this range.
Focus on low-fiber, high-glycemic carbs: Choose easily digestible foods like white rice, pasta, and bagels to prevent stomach upset and maximize absorption.
Combine with exercise tapering: A reduction in training volume in the days leading up to the race allows your muscles to store the extra glycogen efficiently.
Stay hydrated and don't worry about weight gain: Glycogen binds with water, so temporary weight gain is normal and beneficial for hydration and fuel storage.
Test your strategy during training: Experiment with timing and food choices before long runs to ensure your race-day plan works for your body.
Carb load is for events over 90 minutes: A dedicated carb load is most beneficial for endurance events like marathons, not necessary for shorter races like a 5K.

Understanding the Science of Carb Loading

Carb loading is a strategy used by endurance athletes to maximize the storage of glycogen in their muscles and liver. Glycogen is the stored form of glucose, which your body uses for energy, particularly during prolonged, high-intensity exercise. Your body's glycogen stores can typically fuel about 90 to 120 minutes of strenuous activity before depletion leads to fatigue. Carb loading helps to fully replenish these stores, ensuring you have enough energy to sustain performance in events lasting longer than 90 minutes.

The Ideal Timing: 24 to 72 Hours Before a Race

Modern recommendations for carb loading suggest a two to three-day period of increased carbohydrate intake combined with reduced training volume (tapering). A long, restrictive depletion phase is generally considered unnecessary and potentially harmful.

For endurance events (over 90 minutes): Aim for 8-12 grams of carbohydrates per kilogram of body weight per day during the 1-3 days before the race.
For shorter races (under 90 minutes): A dedicated carb load is usually not required. Ensuring a balanced diet and a carbohydrate-rich meal a few hours before the event is typically sufficient.

Strategic Carb Loading vs. "Stuffing Your Face"

Effective carb loading is about strategic eating, not simply consuming excessive amounts of food. The focus is on increasing the proportion of carbohydrates in your diet while reducing fat and fiber intake to avoid digestive issues. Distributing carbohydrate intake throughout the day with multiple meals and snacks can help manage discomfort. It's crucial to test your carb loading plan during training to understand how your body reacts.

Comparison of Carb Loading Strategies


Strategy	Duration	Carbohydrate Intake Target	Key Considerations
Classic Method (Outdated)	6-7 days	High carb (60-70% total energy) after depletion	Included a glycogen-depleting phase; considered unnecessary by modern standards.
Modern Approach (2-3 Day)	2-3 days	8-12 g/kg body weight per day	Focuses on tapering exercise and increasing carbohydrate ratio; reduces risk of GI issues.
Last-Minute Load	1 day	10-12 g/kg body weight per day	Requires consuming a large quantity of carbs in a short time; less gentle on the digestive system.
Female-Specific Loading	2-4 days	Higher total calorie intake alongside high carbs	Women may require a higher caloric intake (around 34% more) to achieve the same glycogen supercompensation as men, due to hormonal differences.

Tips for a Successful Carb Load

Prioritize easy-to-digest carbohydrates. Opt for low-fiber options such as white rice, pasta, peeled potatoes, bagels, and fruit juices to minimize the risk of stomach upset.
Reduce fiber, fat, and protein. Limit intake of these macronutrients as they can slow digestion and make it challenging to consume sufficient carbohydrates. Choose lean protein sources and moderate vegetable portions.
Stay well-hydrated. Glycogen storage is linked to water retention, with approximately three grams of water stored for every gram of glycogen. Adequate fluid intake is essential for effective glycogen loading.
Expect temporary weight gain. The increase in weight is due to the extra water stored with glycogen and is a normal indicator of successful carb loading.
Practice during training. Experiment with your carb loading strategy before long training sessions to identify what works best for your body before race day.

What to Eat: A Sample Carb-Loading Day

Below is a sample daily menu for a 70kg athlete targeting approximately 700g of carbohydrates during the carb-loading phase:

Breakfast: Large portion of white rice or oatmeal with honey and a banana, plus fruit juice.
Morning Snack: A large bagel with jam and a sports drink.
Lunch: Large serving of white pasta with a simple tomato sauce and a small piece of grilled chicken.
Afternoon Snack: Pretzels and fruit juice or a low-fiber energy bar.
Dinner (night before): Plain baked potato with minimal toppings and a small serving of lean meat.
Evening Snack: Rice pudding or a sweetened sports drink.

Conclusion: Timing and Strategy are Key

Optimal carb loading involves a strategic increase in easily digestible carbohydrate intake for 1-3 days before an endurance race, combined with reduced training volume. This approach effectively maximizes muscle glycogen stores, providing the sustained energy necessary for events longer than 90 minutes. Practicing your fueling strategy during training, focusing on low-fiber and low-fat foods, and maintaining hydration are vital steps for race-day success.

Common Carb Loading Mistakes

Waiting too late: A single high-carb meal the night before is generally insufficient for optimal glycogen loading.
Eating too much fiber: High-fiber foods can lead to digestive discomfort during the race.
Neglecting hydration: Inadequate fluid intake can hinder the amount of glycogen your body can store.
Starting too early: Beginning the carb load too far in advance may lead to unnecessary weight gain and discomfort without additional performance benefits.
Introducing new foods: Stick to familiar foods during the carb-loading period to avoid unexpected stomach issues on race day.

For personalized advice, consult an accredited sports dietitian to develop a tailored race-day fueling plan.

Frequently Asked Questions

The main goal of carb loading is to maximize the storage of glycogen in your muscles and liver before an endurance event. This ensures your body has a readily available and easily accessible energy source to delay fatigue and sustain performance during long races.

Not necessarily. Effective carb loading involves shifting your macronutrient ratio to prioritize carbohydrates, while reducing intake of fat and fiber. This allows you to consume the necessary amount of carbs without feeling overly full or sluggish.

Yes, research indicates that women may need to increase their total caloric intake more significantly than men (around 34% more) during the loading phase to achieve similar levels of glycogen supercompensation. This is due to hormonal differences affecting carbohydrate metabolism.

Yes, temporary weight gain of 1-2kg is normal during carb loading and is a positive sign that your body is storing extra glycogen along with water. This water retention is beneficial for maintaining hydration during the race.

The night before the race, focus on a familiar, carbohydrate-heavy meal that is low in fiber and fat to prevent stomach issues. Examples include white pasta with a simple sauce or white rice with grilled chicken. Aim for a slightly earlier dinner to allow plenty of time for digestion.

Your race morning breakfast should be eaten 2-4 hours before the race and consist of 1-4 grams of easily digestible carbohydrates per kilogram of body weight. Stick to foods you have practiced with during training, like oatmeal, a bagel with jam, or a banana.

No, a dedicated carb load is generally not necessary for races lasting less than 90 minutes. For these events, your regular balanced diet and a solid pre-race meal should provide enough energy.