What is carb loading for race prep? A comprehensive nutrition guide

October 14, 2025 •

3 min read

Scientific studies show that carbohydrate loading can improve endurance performance by 2-3% in events lasting longer than 90 minutes. This strategy, known as what is carb loading for race prep, is a deliberate and timed increase in carbohydrate intake to maximize your body's energy reserves before an event.

Quick Summary

Carb loading is a nutrition strategy for endurance athletes that involves increasing carbohydrate intake in the days before a long race. It helps maximize muscle and liver glycogen stores to prevent fatigue and sustain performance during events over 90 minutes long.

Key Points

Maximizes Glycogen Stores: Carb loading increases your body's reserve of stored carbohydrates (glycogen) in your muscles and liver.
Delays Fatigue: Higher glycogen levels help postpone muscle fatigue, allowing you to maintain a higher intensity for longer durations.
Recommended for Endurance Events: This strategy is most beneficial for races lasting longer than 90 minutes, such as marathons and triathlons.
Timed with Training Taper: The carb-loading phase typically starts 2-3 days before the race, coinciding with a reduction in your training intensity.
Focus on Digestible Carbs: Emphasize low-fiber, easily digestible carbohydrates like white rice, pasta, and bananas while reducing fat and fiber intake.
Practice in Training: Experiment with your carb-loading meals and timing during your long training runs to avoid stomach issues on race day.

The Science of Carbohydrate Loading

Carbohydrates are the primary fuel source during high-intensity, prolonged exercise, converted into glucose and stored as glycogen in muscles and the liver. This stored glycogen powers sustained energy output during events like marathons. Normally, glycogen stores last about 90 minutes, after which the body relies more on less efficient fat metabolism, leading to fatigue or "hitting the wall". Carb loading aims to increase these glycogen reserves significantly, providing a larger fuel capacity for race day, delaying fatigue, and optimizing performance in endurance events.

When and How to Carb Load Effectively

The current approach to carb loading involves increasing carbohydrate intake for two to three days before an event while reducing training volume (tapering). This combination enhances muscle glycogen storage. The recommended intake is 8 to 12 grams of carbohydrates per kilogram of body weight daily. This high volume can be challenging to consume through solid food alone, so spreading intake across multiple meals and snacks, and incorporating liquid carbohydrates like juice or sports drinks, is often advised.

Fueling Choices: The Best Foods for Carb Loading

Selecting appropriate foods is vital to avoid gastrointestinal issues on race day. The focus is on carbohydrate-dense options that are low in fiber and fat. While whole grains are beneficial daily, refined carbohydrates are often preferred in the final 48 hours for easier digestion.

High-Carb Food Options

Grains: White pasta, white rice, low-fiber cereal, bagels, white bread.
Starchy Vegetables: Peeled potatoes and sweet potatoes.
Fruits: Bananas, fruit juice, applesauce.
Dairy and Desserts: Low-fat yogurt, milk, honey, maple syrup.
Liquid Carbs: Sports drinks.

Foods to Limit During Carb Loading

High-fiber vegetables (broccoli, legumes).
Fatty foods (rich sauces, pizza, pastries).
High-protein foods.

Comparison of Carb-Loading Strategies


Feature	3-Day Carb Load (Standard Method)	1-Day Carb Load (Accelerated Method)
Timing	Starts 2-3 days before the race.	Performed the day before the race.
Carb Goal	8-10 g/kg of body weight per day.	10-12 g/kg of body weight per day.
Ease of Intake	More gradual intake, easier to digest.	Large amount of carbs in shorter time; may cause bloating.
Best For	Marathons and other long events (>90 minutes).	Shorter endurance events or limited time.
Athletic Taper	Coincides with the training taper.	Performed during a rest day.

Potential Downsides and Mistakes

Carb loading can lead to a temporary weight gain of 1-2kg due to water stored with glycogen, which is beneficial for hydration. Digestive issues like bloating can occur if too much fiber or fat is consumed. To mitigate risks, practice your carb loading during training to identify suitable foods and quantities. Spreading intake across smaller meals also aids digestion. Avoid new foods or supplements during race week.

Race Day Nutrition: The Final Fueling

A carb-rich breakfast 2-3 hours before the race helps replenish liver glycogen and stabilize blood sugar. This meal should be familiar, easily digestible, and moderate in fat and protein. During events over an hour, consume 30-60 grams of simple carbohydrates per hour from gels, chews, or sports drinks, starting early. Combining glucose and fructose can improve absorption. Hydration is also essential throughout the race.

Conclusion

What is carb loading for race prep? It's a key strategy for endurance athletes to boost performance by maximizing glycogen stores. Proper carb loading, timed with a training taper and focusing on easily digestible carbohydrates, can delay fatigue and improve performance in events over 90 minutes. Practicing your strategy and selecting the right foods are crucial for success. With careful planning, you can be well-fueled and ready for race day. For additional information, Runner's World provides a helpful guide on carb loading.

Authoritative Link

Runner's World - Carb loading: How to get it right ahead of a marathon: https://www.runnersworld.com/uk/nutrition/diet/a27178213/when-to-start-carb-loading-marathon/

Frequently Asked Questions

For most endurance events, you should begin carb loading 2 to 3 days before the race. This timing, combined with a reduction in training, allows your body to maximize glycogen storage.

Most experts recommend consuming 8 to 12 grams of carbohydrates per kilogram of body weight per day during the carb-loading phase. For example, a 70kg athlete would aim for 560 to 840 grams daily.

You are not necessarily eating more total calories, but rather adjusting the proportion of your calories. You increase carbohydrates while reducing fat and protein intake to make room for the extra carbs.

Focus on easily digestible, lower-fiber carbohydrates such as white pasta, white rice, peeled potatoes, bananas, and sports drinks. Avoid excessive fiber and fat to prevent digestive issues.

Yes, it is normal and expected to gain a few pounds. Your body stores extra water with every gram of glycogen, which is a good sign that your fuel tank is full.

While a pasta dinner is a classic pre-race meal, consuming a single, excessively large meal can cause digestive issues and leave you feeling sluggish. It's better to spread your carbohydrate intake across multiple smaller meals over 2-3 days.

No, carb loading is not typically necessary for shorter events like a 5K or 10K. Your body's regular glycogen stores are usually sufficient for races lasting less than 90 minutes.