Why Carbohydrates Matter for Endurance
Carbohydrates are the primary fuel for endurance exercise, and your muscle and liver glycogen stores are critical for maintaining performance. Your body converts carbohydrates into glucose, which is stored as glycogen in the muscles and liver. During exercise, your body breaks down glycogen to provide quick energy. When glycogen runs low, you may experience a sudden drop in energy, heavy legs, dizziness, mental fog, and a noticeable decline in performance—often called 'hitting the wall' or 'bonking.'
Endurance athletes who do not consume enough carbohydrates may not meet their energy needs. In fact, up to 80% of endurance runners do not consume enough carbohydrates to support their training. Understanding your daily carbohydrate needs and how to time intake around exercise can help you avoid glycogen depletion and perform at your best.
Sources: Gatorade Sports Science Institute, University of Illinois, Utah State University Extension
Daily Carbohydrate Targets for Endurance Athletes
Your daily carbohydrate needs depend on the intensity and duration of your training. For moderate-to-high-intensity training lasting 1–3 hours per day, aim for 6–10 grams of carbohydrate per kilogram of body weight. If you train 4–5 hours per day, increase that to 8–12 grams per kilogram. For example, a 70-kg (154-pound) athlete training 1–3 hours per day would need roughly 420–700 grams of carbohydrate daily. This range typically provides 45–65% of your total daily calories, which is the recommended proportion for endurance athletes.
These targets are general guidelines; individual needs vary based on body size, training load, and metabolic factors. Working with a sports dietitian can help tailor the numbers to your specific routine.
Sources: Utah State University Extension, University of Illinois
Carbohydrate Periodization Basics
Carbohydrate periodization means adjusting your carbohydrate intake to match the demands of your training. On heavy training days, you consume more carbohydrates; on easy days or rest days, you reduce intake. This approach can help align fuel availability with the work your body is doing, potentially improving adaptation and performance.
Periodization is not a long-term strategy and requires careful planning. It is not about training low all the time; rather, it is a deliberate manipulation of carb availability around key sessions. If you are considering low-carb training periods, understand that they may impair high-intensity performance and should be used strategically under professional guidance.
Sources: Gatorade Sports Science Institute
Pre-race
Eating a carbohydrate-rich meal in the hours before exercise helps top off your glycogen stores. For exercise lasting more than 60 minutes, consume 1–4 grams of carbohydrate per kilogram of body weight 1–4 hours before you start. A 70-kg athlete might start with 70 grams (1 g/kg) and adjust downward based on tolerance and timing. Choose low-fiber, easily digestible sources to minimize gastrointestinal discomfort. Plain bread, rice, pasta, bananas, or sports drinks are good options.
If you are preparing for a race longer than 90 minutes, you may benefit from carb loading. This involves consuming 10–12 grams of carbohydrate per kilogram of body weight per day for 36–48 hours before competition while tapering your exercise. A 150-pound (68-kg) athlete would need roughly 680–816 grams of carbs per day during this short period. Carb loading can help maximize glycogen stores, giving you an extra edge in events over 90 minutes.
Sources: Gatorade Sports Science Institute, Utah State University Extension, University of Illinois
During-Exercise Fueling Strategies
For exercise sessions lasting longer than 60–90 minutes, you need to replace carbohydrates during the event to maintain blood glucose levels and spare your glycogen stores. Aim for 30–60 grams of carbohydrate per hour for the first few hours. For ultra-endurance events lasting more than 2.5–3 hours, some athletes tolerate up to 90 grams per hour, and recent evidence suggests up to 120 grams per hour may be beneficial.
To reach higher intakes, you need to consider the type of carbohydrate. Combining glucose with fructose can improve absorption and reduce the risk of gut upset. A ratio near 1:0.8 (glucose to fructose) appears to optimize oxidation and gut comfort. Gels, sports drinks, chews, bananas, and dates are practical sources; choose ones you have tested in training to avoid stomach issues on race day.
Sources: Gatorade Sports Science Institute
Post-Exercise Glycogen Replenishment
After exhaustive exercise, your muscle glycogen stores are depleted, and replenishing them is key for recovery. Consume 1.0–1.2 grams of carbohydrate per kilogram of body weight per hour during the first 4 hours after exercise. For a 70-kg athlete, that is about 70–84 grams per hour. Moderate-to-high glycemic index carbohydrates—such as white bread, sports drinks, or pasta—are more effective for rapid glycogen resynthesis than low-glycemic options.
If you cannot eat solid food immediately after a workout, a sports drink or smoothie can provide carbs and fluids. Combine this with protein for muscle repair, but the post-exercise emphasis for glycogen is on carbohydrate timing and amount.
Sources: Gatorade Sports Science Institute
Common Carbohydrate Myths and Mistakes
Many endurance athletes underfuel because they fear carbohydrates will cause weight gain, or they believe low-carb training is superior. However, up to 80% of endurance runners do not consume enough carbohydrates to meet their training needs, which can compromise performance and recovery.
Another common mistake is relying solely on high-protein or fat-rich meals during heavy training periods. While these nutrients have their place, they cannot replace the rapid energy provided by carbohydrates. Additionally, ignoring pre-exercise meal timing or consuming too much fiber too close to exercise can lead to gastrointestinal distress. Practice your fueling plan during training to minimize surprises on race day.
Sources: Utah State University Extension, University of Illinois
Frequently asked questions
How many grams of carbs do I need per hour during endurance exercise?
During exercise lasting longer than 60–90 minutes, aim for 30–60 grams of carbohydrate per hour. For ultra-endurance events exceeding 2.5–3 hours, some athletes may benefit from up to 90 grams per hour, and recent research suggests up to 120 grams per hour in certain circumstances. To absorb higher amounts, combine glucose and fructose (e.g., in a 1:0.8 ratio) to enhance oxidation and reduce stomach discomfort.
Sources: Gatorade Sports Science InstituteWhat is carb loading and who should do it?
Carb loading is a short-term strategy to maximize muscle glycogen stores before an event lasting longer than 90 minutes. It involves consuming 10–12 grams of carbohydrate per kilogram of body weight per day for 36–48 hours before competition while tapering exercise. It is not necessary for shorter events or routine training sessions.
Sources: Gatorade Sports Science Institute, University of Illinois, Utah State University ExtensionAre low-carb training zones beneficial for endurance?
Low-carb training may have a role in certain periodized plans, but it is not a long-term strategy and requires careful planning. The evidence on benefits is not fully detailed, and low-carb training can impair high-intensity performance. It should be used strategically and under professional guidance, not as a standard approach for all endurance athletes.
Sources: Gatorade Sports Science InstituteWhat are the best carb sources for athletes?
The best sources depend on timing. For everyday meals, choose whole grains, fruits, vegetables, and legumes to meet daily needs. Before and during exercise, opt for low-fiber, easily digestible sources like white bread, rice, pasta, bananas, sports drinks, and gels. After exercise, moderate-to-high glycemic index carbs such as sports drinks, white bread, or pasta help replenish glycogen quickly.
Sources: Gatorade Sports Science Institute, University of Illinois, Utah State University ExtensionCan I rely on gels and sports drinks for carbs?
Gels and sports drinks are convenient during exercise, but they are not necessary for all training. They are especially useful for longer sessions (>60–90 min) where you need quick, easily digestible carbohydrates. However, for daily fueling, whole-food sources provide additional nutrients and should be the foundation of your diet. Test any commercial product in training to ensure it works for you.
Sources: Gatorade Sports Science Institute, Utah State University ExtensionSources
- Dietary Carbohydrate And Endurance Athletes — Gatorade Sports Science Institute
- CHAPTER 3 – CARBS: THE SECRET WEAPON FOR ENDURANCE ATHLETES — University of Illinois
- Prioritizing Carbohydrates: A Guide for Endurance Runners — Utah State University Extension