Why Carbohydrates Are a Runner's Primary Fuel
Your body, much like a high-performance engine, has a preferred fuel type. For a runner, this is carbohydrates. When you consume carbs, your body breaks them down into glucose, which is then stored in your muscles and liver as glycogen. This glycogen is the most readily available and efficient energy source for moderate to high-intensity exercise, including most running activities. When these stores are depleted, a runner experiences significant fatigue, famously known as "hitting the wall".
Fueling for the long run
- Replenishing Glycogen: For runs lasting more than 90 minutes, your glycogen stores will be significantly depleted. A sports dietitian will recommend that your daily carbohydrate intake directly reflects your training volume. The higher your mileage, the higher your carbohydrate needs.
- Mid-Run Boost: For efforts over an hour, consuming 30–60 grams of carbohydrates per hour helps maintain blood glucose levels and delays fatigue. This can be achieved through gels, chews, or sports drinks.
- Carb Loading: Before an endurance race, a strategic increase in carbohydrate intake over 2-3 days saturates muscle glycogen stores, boosting performance by 2–3% and endurance by 15–25% for events longer than 90 minutes.
The Critical Role of Protein for Recovery and Repair
While carbs provide the energy to run, protein provides the raw materials to recover and rebuild. Protein is not a primary fuel source during a run but becomes essential for repairing the microscopic tears that occur in muscle fibers during intense and long-distance training. Proper protein intake helps facilitate muscle protein synthesis, strengthens the immune system, and helps prevent muscle loss.
Timing is everything for muscle repair
- The Post-Run Window: Consuming 15–30 grams of high-quality protein within 30–60 minutes after a run is ideal for jumpstarting the recovery process. This timing is particularly important because your muscles are most receptive to rebuilding during this window.
- Daily Distribution: Spreading protein intake evenly throughout the day, rather than in one large meal, maximizes its benefits for muscle repair and overall health. Good protein sources include lean meats, fish, eggs, dairy, and plant-based options like legumes and tofu.
Comparison: Carbs vs. Protein for Runners
To illustrate the distinct roles of these two macronutrients, consider the following comparison based on a 70kg endurance runner during a high-mileage training block:
| Feature | Carbohydrates | Protein |
|---|---|---|
| Primary Role | Main energy source for high-intensity and endurance exercise. | Muscle repair, rebuilding, and immune function. |
| Daily Intake (70kg runner) | 420-700g (6-10 g/kg). | 84-140g (1.2-2.0 g/kg). |
| Timing During a Run | Critical for runs >60 mins (30-60g/hour). | Not used as primary fuel, generally avoided during run. |
| Timing After a Run | First priority to replenish glycogen (1-1.2g/kg in 4hrs). | Important within 30-60 mins post-run for repair (15-30g). |
| Best Sources | Whole grains, pasta, rice, fruits, starchy vegetables. | Lean meat, poultry, fish, eggs, dairy, legumes, tofu. |
| Deficiency Risks | Early fatigue, "hitting the wall," poor recovery. | Slow recovery, muscle damage, increased injury risk. |
Creating a Balanced Runner's Diet
A well-rounded diet for a runner emphasizes a higher ratio of carbohydrates to protein, with the specific amounts tailored to individual training needs. For a general fitness runner, a macro split of around 50% carbs, 20% protein, and 20% fat is a good starting point. For a serious marathoner, the carbohydrate percentage might increase to 55-60%, especially during peak training weeks. However, as sports physiologist Asker Jeukendrup points out, focusing on the absolute quantity of macronutrients based on training load is more important than sticking rigidly to percentages.
Ultimately, the goal is not to choose between carbs and protein but to optimize both. Fuel high-intensity runs with carbohydrates and ensure your recovery meals include both carbs and high-quality protein to repair and rebuild effectively. A balanced diet, personalized to your activity level, remains the most effective strategy for sustained running performance and health.
The Role of Periodized Nutrition
Carbohydrate needs are not static. They should be periodized, meaning your intake should vary depending on your training cycle. On rest days or low-intensity days, a moderate carbohydrate intake is sufficient. During periods of high mileage or intense training, carbohydrate consumption should increase substantially to keep glycogen stores full. This strategic approach, combined with consistent protein intake, allows your body to maximize adaptations from your training and minimize the risk of overtraining syndrome or relative energy deficiency in sport (RED-S).
Conclusion
In summary, runners absolutely should eat more carbohydrates than protein to adequately fuel endurance training and performance. Carbohydrates serve as the body's primary and most efficient energy source, while protein is vital for muscle repair and recovery post-exercise. Instead of viewing these macronutrients as a competition, a runner's nutritional strategy should prioritize both by emphasizing a higher overall volume of carbohydrates, especially around workouts, and ensuring consistent, high-quality protein intake throughout the day to support recovery. Ultimately, a balanced and individualized approach to fueling will lead to better performance and a healthier running journey.
