Nutrition Diet: How to calculate carbohydrate load?

October 16, 2025 •

4 min read

Research indicates that proper carbohydrate loading can enhance endurance by up to 15-25% for events lasting over 90 minutes. For competitive athletes, understanding how to calculate carbohydrate load accurately is the key to maximizing muscle glycogen and avoiding fatigue on race day.

Quick Summary

Carbohydrate loading is a nutritional strategy used by endurance athletes to increase the body's glycogen stores. The process typically involves consuming a high-carb diet for 1 to 3 days before an event, accompanied by reduced exercise to maximize energy reserves.

Key Points

Body Weight Formula: Calculate your daily carb target at 8-12 grams per kilogram of body weight for 1-3 days before an endurance event.
Modern Method: Focus on a 1-3 day high-carb load with reduced training, rather than the older, more stressful depletion phase.
Food Selection: Prioritize easy-to-digest, low-fiber carbs like white pasta, rice, and fruit juices to avoid gastrointestinal issues.
Practice is Essential: Always test your carb loading strategy during a long training run or event rehearsal to understand your body's response.
Hydration Matters: Increase your fluid intake, as each gram of stored glycogen holds onto 3-4 grams of water, contributing to a temporary but beneficial weight gain.
Balance Macronutrients: While increasing carbs, slightly reduce fat and protein intake to make room for the higher carb volume without over-consuming calories.
Event Suitability: Carb loading is most beneficial for endurance events lasting over 90 minutes and is unnecessary for shorter duration activities.

Understanding the Science of Carb Loading

Carbohydrate loading is a strategic dietary plan used by endurance athletes to maximize the storage of glycogen in their muscles and liver. Glycogen is the body's main energy source for high-intensity, prolonged exercise, and sufficient stores are crucial for delaying fatigue and improving performance in events over 90 minutes, such as marathons or long-distance cycling. The modern approach to carb loading focuses on a 1-3 day regimen of high carbohydrate intake, eliminating the need for the older, more stressful depletion phase.

The Body Weight Formula: How to calculate carbohydrate load?

The most precise and widely recommended method for calculating your carbohydrate load is based on your body weight. The formula provides a target range of carbohydrate intake in grams per kilogram (g/kg) of body weight.

For most endurance events, athletes should aim for the following intake for 1-3 days leading up to the competition:

For events over 90 minutes: 8-12 grams of carbohydrates per kilogram of body weight per day.
For events around 90 minutes: 6-8 grams of carbohydrates per kilogram of body weight per day.

Example Calculation:

Athlete Weight: 70 kg
Event: Marathon (over 90 minutes)
Target: Aim for 10 g/kg per day.
Calculation: 70 kg × 10 g/kg = 700 grams of carbohydrates per day.

This target of 700 grams per day would be consumed over 1-3 days before the race, depending on the athlete's strategy and tolerance. It's crucial to spread this intake across multiple meals and snacks throughout the day to avoid feeling overly full or bloated.

Practical Steps to Hit Your Carbohydrate Target

To put the calculated target into practice, athletes need to plan their meals and choose their food sources wisely. The focus should be on carbohydrate-dense, low-fiber options to facilitate easy digestion and avoid gut issues on race day.

Planning a 700g Carb Day:

Breakfast (approx. 200g carbs): Large bowl of low-fiber cereal with milk and a sliced banana, plus a large glass of orange juice.
Mid-Morning Snack (approx. 100g carbs): Two bagels with jam or honey.
Lunch (approx. 200g carbs): Large plate of pasta with a low-fat marinara sauce and white bread rolls.
Afternoon Snack (approx. 100g carbs): Pretzels and a sports drink.
Dinner (approx. 100g carbs): White rice with grilled chicken or fish, and low-fat yogurt.

Important Considerations:

Hydration: For every gram of glycogen stored, the body stores about 3-4 grams of water. It is vital to increase fluid intake during the loading phase to aid absorption and stay well-hydrated. This water weight is temporary and a positive sign of successful loading.
Reducing Fat and Fiber: While increasing carbohydrate intake, it is necessary to slightly reduce the amount of fat and fiber you consume. Fat is calorically dense and can slow digestion, while too much fiber can cause gastrointestinal distress.
Listen to Your Body: What works for one athlete may not work for another. Practicing your carb loading strategy during a long training session is essential to assess your body's response and tolerance.

Comparison of Carb Loading Strategies


Strategy	Duration	Key Features	Pros	Cons
Classic 7-Day	7 days	Initial 3-4 day depletion phase followed by 3-4 day high-carb load.	Maximizes glycogen stores through a 'supercompensation' effect.	Can cause mood swings, fatigue, and digestive issues during the depletion phase.
Modern 1-3 Day	1-3 days	High-carb intake (8-12g/kg/day) paired with tapered exercise.	More practical, less demanding on the athlete, reduces risk of digestive upset.	Might not achieve the absolute highest level of glycogen supercompensation for all individuals.
Single-Day Load	1 day	A very high-carb intake on the day before the event.	Easiest and simplest approach, though less effective for maximizing stores compared to multi-day methods.	Very high volumes of food or drink may be hard to consume and digest in a short period.

Choosing Carbohydrates for an Effective Load

Selecting the right types of carbohydrates is as important as the quantity. During the 1-3 day loading phase, focus on foods that are high in carbs and low in fiber to promote fast digestion and optimal absorption.

Best Choices for Carb Loading:

Refined Grains: White bread, white rice, pasta, crackers.
Starchy Vegetables (no skin): Mashed potatoes, sweet potatoes (no skin).
Fruits: Bananas, applesauce, fruit juices.
Snacks: Pretzels, low-fiber cereals, rice cakes.
Sports Nutrition: Gels, chews, and sports drinks can be very helpful for topping off stores without feeling full.

Foods to Limit or Avoid:

High-Fiber Foods: Beans, legumes, whole grains, and high-fiber vegetables can cause bloating and discomfort.
High-Fat Foods: Fried foods, creamy sauces, and fatty meats slow down digestion.
Excessive Protein: While important, too much protein can reduce the space for carbohydrates and slow absorption.

Conclusion

Calculating your carbohydrate load based on your body weight is a scientifically backed strategy for maximizing your performance in endurance events. By adopting the modern 1-3 day approach, selecting easily digestible, high-carb foods, and tapering your training, you can ensure your muscles are fully fueled for race day. Remember, personal tolerance and practice runs are key to perfecting your individual strategy. Consult with a sports dietitian for personalized advice, especially if you have pre-existing health conditions like diabetes. This methodical approach will help you cross the finish line feeling stronger and more energized. For more detailed information on sports nutrition, you can visit Healthline's comprehensive resources on the topic.

Frequently Asked Questions

Carb loading is primarily recommended for endurance athletes preparing for events lasting 90 minutes or longer, such as marathons, triathlons, and long-distance cycling races.

You should begin your carb loading phase 1 to 3 days before your event. This timeframe allows your muscles to maximize glycogen storage effectively.

The best carbs for loading are low-fiber, easy-to-digest options like white bread, white rice, pasta, and potatoes without skin. Sports drinks and gels can also be used to increase intake.

Yes, a temporary weight gain of 2-4 lbs is normal and expected. This is due to the extra water stored with glycogen and is a positive sign that the loading is working.

Yes, to make room for the increased carbohydrate intake without gaining excess weight, it is generally recommended to slightly decrease your fat intake. Protein should be maintained, but not in excess.

No, carb loading is generally not necessary for shorter events like a 5K, as your body's standard glycogen stores are sufficient to fuel the effort. Focus instead on a balanced daily diet.

Common mistakes include consuming too much fiber, eating high-fat foods, not tapering exercise, or trying new foods right before a race. These can all lead to digestive issues or reduced glycogen storage.

Modern research suggests that a depletion phase is unnecessary and potentially counterproductive. The more effective strategy is a shorter 1-3 day high-carb load combined with reduced training.