The science of mid-run fueling
When you run, your body uses two primary fuel sources: fat and carbohydrates. While your fat stores are plentiful, your body’s supply of stored carbohydrates, known as glycogen, is limited. As a general rule, your glycogen stores can sustain moderate to high-intensity exercise for about 60 to 90 minutes. Past this point, your body relies on consuming external carbohydrates to maintain blood sugar levels and keep your muscles firing.
Without a proper fueling strategy, you risk 'hitting the wall'—a sudden and significant drop in energy caused by depleted glycogen stores. This is where strategic mid-run nutrition becomes critical, providing a consistent supply of fast-acting energy to power you through your entire workout or race.
How to fuel for different run durations
Your fueling needs are not one-size-fits-all. The length and intensity of your run will determine whether you need to eat mid-run and how much carbohydrate to consume.
Short runs (under 60 minutes)
For most runners, a pre-run meal or snack is sufficient for a run lasting less than an hour. Your body's existing glycogen stores will provide enough energy. Focusing on a balanced diet rich in complex carbohydrates on a day-to-day basis is the priority. However, during particularly intense sessions, some athletes may benefit from a small amount of fuel, and it is always a good time to practice your hydration routine.
Moderate to long runs (60 minutes to 3 hours)
This is the sweet spot for mid-run fueling. Experts recommend consuming 30-60 grams of easily digestible carbohydrates per hour to maintain energy levels. You should begin fueling early, starting at around the 30 to 45-minute mark, and then continue with consistent intake every 30 to 45 minutes.
Ultra-endurance runs (over 3 hours)
For runs exceeding three hours, your body's energy demands increase significantly. The carbohydrate intake recommendations go up to 60-90 grams per hour. In these longer events, you may also need to consider taking in a small amount of protein, around 5 grams per hour, to help with muscle function and repair. The key is to train your gut to handle this higher volume of fuel without causing gastrointestinal distress.
Your fueling options: Gels, chews, and real food
What you choose to eat during a run depends on personal preference, stomach sensitivity, and the convenience of the format. Most fueling options are designed to deliver simple carbohydrates quickly and efficiently.
Comparison of mid-run fueling options
| Fuel Type | Carbohydrates | Convenience | Digestion Rate | Pros | Cons |
|---|---|---|---|---|---|
| Energy Gels | 20-30g per packet | High (small, easy to carry) | Fastest | Quick energy, easy to consume at high intensity | Syrupy texture, potential for stomach upset if not taken with water |
| Energy Chews | Varies (e.g., 4-5 blocks) | High (can meter intake) | Fast | More satisfying to eat, less messy than gels | Requires chewing, can get sticky, may slow down consumption rate |
| Sports Drinks | Varies (e.g., 30g per 2 cups) | High (can hydrate simultaneously) | Fast | Replaces fluids, carbs, and electrolytes all at once | Bulkier to carry than gels/chews, can cause GI issues if too concentrated |
| Real Food | Varies (e.g., 1 banana ≈ 30g) | Moderate | Varies (depending on source) | More natural, palatable, and cost-effective | Less concentrated, requires more chewing, difficult to carry larger quantities |
Don't forget hydration and electrolytes
Fueling goes hand-in-hand with hydration. Dehydration can compromise your performance and trigger gastrointestinal issues, even if you are consuming enough carbohydrates. For runs lasting more than an hour, especially in hot or humid conditions, it is crucial to consume water and replace lost electrolytes, primarily sodium.
- Replenish fluids: Aim to drink water regularly throughout your run, typically 100-200ml every 20 minutes. Your specific needs will depend on your sweat rate, which can be determined with a simple pre-and post-run weight test.
- Replace electrolytes: For longer efforts, plain water may not be enough. Electrolyte drinks, tablets, or even salty snacks like pretzels can help replace sodium and other minerals lost through sweat. This helps maintain fluid balance and prevents cramping.
How to practice your mid-run nutrition strategy
Never try a new fueling strategy on race day. Your training runs are the perfect opportunity to experiment and train your gut. Consistency is key, and your body can adapt over time to tolerate more food while running.
- Start simple: Begin with smaller amounts of fuel during your longest runs to see how your stomach reacts.
- Test different options: Try out various brands and flavors of gels, chews, and drinks to find what you tolerate and enjoy. Many runners rotate flavors to prevent palate fatigue during long events.
- Simulate race day: Practice your exact fueling plan during your long runs, using the same products you intend to use on race day. Note how you feel in a running journal to refine your strategy.
Conclusion
For any run lasting more than 60-90 minutes, a consistent and well-rehearsed fueling strategy is non-negotiable for sustained performance. The best fuel sources are easily digestible carbohydrates like gels, chews, and certain real foods, which should be consumed with water and electrolytes at regular intervals. By practicing your fueling plan during training, you can discover what works best for your body, ensuring you have the energy needed to finish strong. For more detailed guidance, consider consulting a sports dietitian to craft a personalized nutrition plan.
