What is Considered Carb Loading and How Can it Boost Performance?

December 17, 2025 •

3 min read

Studies have shown that effective carb loading can improve athletic endurance by 15-25% for events lasting over 90 minutes. So, what is considered carb loading? It's a strategic dietary practice used by endurance athletes to maximize their body's stored energy before a major competition.

Quick Summary

Carb loading is a nutritional strategy for endurance athletes to maximize muscle glycogen stores. It involves increasing carbohydrate intake while reducing training volume in the days leading up to an event, providing a powerful energy reserve to delay fatigue.

Key Points

Strategic Fueling: Carb loading is an athlete's strategy to maximize muscle and liver glycogen stores by increasing carbohydrate intake before an endurance event.
Purpose for Performance: The goal is to delay the onset of fatigue ('hitting the wall') in high-intensity activities lasting longer than 90 minutes.
Modern Method: Current practices favor a 1- to 3-day high-carb phase (8-12g/kg body weight) paired with reduced training, avoiding the harsh 'depletion' phase.
Focus on Low-Fiber Carbs: Choosing easily digestible, low-fiber carbohydrates helps prevent gastrointestinal distress on race day.
Expect Temporary Weight Gain: An increase of 1-2kg in body weight is normal during carb loading, as glycogen is stored alongside water, which is a sign of effective fuel storage.
Practice Makes Perfect: Athletes should practice their carb-loading plan during training to determine which foods and timing work best for their body.

The Science Behind Carb Loading

Carbohydrate loading, or 'carb loading', is a nutritional technique designed to elevate the amount of glycogen stored in the body's muscles and liver. Glycogen is the body's most readily available energy source, and maximizing these stores is crucial for prolonged, high-intensity exercise, such as a marathon or triathlon. During endurance events that last longer than 90 minutes, the body's normal glycogen stores can become depleted, leading to a significant drop in performance known as 'hitting the wall'. By saturating the body with carbohydrates beforehand, athletes create a deeper reserve of fuel to draw upon during the race, helping to sustain energy levels and delay fatigue.

How Glycogen Storage Works

When you consume carbohydrates, your body breaks them down into simple sugars, primarily glucose. This glucose is then absorbed into the bloodstream. If the body doesn't need all of this glucose for immediate energy, it converts the excess into glycogen and stores it in the muscles and liver for later use. For every gram of glycogen stored, the body also stores approximately three grams of water, which is why a temporary weight gain of a few pounds is common during a carb-loading phase. This water retention is a normal and beneficial part of the process, indicating that your glycogen stores are being topped up effectively.

Carb-Loading vs. Normal Eating

Carb loading is not simply about eating more food. It involves a shift in the proportion of macronutrients consumed, reducing fat and protein to prioritize carbohydrates without drastically increasing total calories. This dietary change is coupled with reduced training volume, or tapering, in the days leading up to the event. This combination of high carbohydrate intake and reduced exercise allows the body to maximize glycogen storage.

Modern vs. Classic Carb-Loading Strategies

The classic carb-loading method previously included a 'depletion phase' followed by a 'loading phase'. However, modern approaches have refined this strategy, largely eliminating the strenuous depletion stage. The modern method typically involves a 1- to 3-day phase combining tapered exercise with a high carbohydrate intake of 8-12 grams per kilogram of body weight daily. This approach is often considered more practical for athletes.

Recommended Foods for Carb Loading

Effective carb loading focuses on high-carbohydrate options that are lower in fat and fiber, particularly in the 24-48 hours before an event. Minimizing fiber can help prevent potential gastrointestinal issues during competition. Specific food recommendations and planning strategies can be found on {Link: STYRKR https://styrkr.com/blogs/training-and-nutrition-hub/carb-loading-before-marathon}.

Comparison of Food Types for Carb Loading


Feature	Low-Fiber Carbs (e.g., White Rice, Pasta)	High-Fiber Carbs (e.g., Whole Grains, Legumes)
Digestion Speed	Fast, easily broken down into glucose for storage.	Slower digestion due to high fiber content.
Potential for GI Issues	Low risk of bloating or discomfort if familiar.	High risk of bloating, gas, or diarrhea during exercise.
Satiety	Less filling, allowing for higher total carbohydrate intake.	More filling due to bulk and fiber, can limit overall carb consumption.
Best Used For	The final 1-3 days before an endurance race.	Part of a balanced, day-to-day training diet.
Nutrient Density	Lower in overall micronutrients compared to whole foods.	Higher in fiber and other nutrients for general health.

Conclusion

In conclusion, what is considered carb loading is a specific and effective nutritional strategy for endurance athletes participating in events lasting over 90 minutes. By increasing carbohydrate intake to 8-12 grams per kilogram of body weight alongside reduced training in the days preceding a race, athletes can maximize their glycogen stores. The modern approach emphasizes a 1- to 3-day strategy, avoiding the demanding older methods. Prioritizing easy-to-digest, low-fiber carbohydrates is crucial for optimal fueling without causing gastrointestinal problems on race day. Practicing your carb-loading strategy during training is essential for a confident and successful performance. For additional information on nutrition strategies, the Sports Dietitians Australia blog is a helpful resource.

Frequently Asked Questions

Carb loading is recommended for endurance athletes, such as marathon runners, long-distance cyclists, and triathletes, who compete in events lasting 90 minutes or longer.

For most athletes, a 36- to 48-hour window before the event is the most effective time to begin carb loading, accompanied by reduced training.

Ideal foods for carb loading include easy-to-digest, high-carbohydrate options like white rice, pasta, bread, potatoes, and fruit juices. Avoid high-fiber and high-fat foods in the final days before the race.

Yes, temporary weight gain of 1-2kg is normal because for every gram of glycogen stored, your body also stores several grams of water. This is a sign of a successful carb load.

Carb loading is not necessary for shorter events like a 5K or 10K, as normal glycogen stores are sufficient. Focusing on a balanced diet and proper hydration is enough.

For a 1- to 3-day load, aim for 8-12 grams of carbohydrates per kilogram of body weight per day. This can be challenging and often requires incorporating liquid carbohydrates.

Yes, you should include moderate amounts of lean protein and small amounts of healthy fats to balance your meals, but the bulk of your calories should come from carbohydrates.