The Science Behind On-Run Fueling
When you run, your body uses two primary fuel sources: fat and carbohydrates. While your body has a vast storage of fat, converting it to energy is a slower process, making carbohydrates the preferred and faster fuel, stored as glycogen in your muscles and liver. These glycogen stores are limited and can be depleted in as little as 60-90 minutes during moderate to intense exercise. Once these stores run out, the body is forced to rely more heavily on fat, leading to a significant drop in performance often called 'hitting the wall' or 'bonking.'
To prevent this, runners must begin consuming easily digestible carbohydrates before total depletion occurs. The goal is to provide a steady supply of energy that the body can use efficiently while running, thereby sparing your remaining glycogen stores and maintaining blood sugar levels.
Determining When to Start Fueling
The most important rule for long-distance fueling is to start before you feel a drop in energy. For runs lasting longer than 75 minutes, a good rule of thumb is to begin taking in carbohydrates around the 30-45 minute mark. From there, you should continue to refuel consistently every 30-60 minutes to maintain steady blood sugar levels.
This early and consistent approach is critical for several reasons:
- Absorption takes time: Your body needs time to digest and absorb the carbohydrates you consume and deliver them to your muscles. Waiting until you feel fatigued means you'll have to endure a performance dip while your body processes the fuel.
- Maintains mental focus: Carbohydrates are not only for your muscles; they also fuel your brain. A drop in blood sugar can impair concentration and decision-making, which can be critical during a race.
- Avoids gastrointestinal distress: By taking smaller, more frequent doses of fuel, you place less stress on your stomach than by trying to consume a large amount of fuel all at once.
Choosing Your Fuel: Gels vs. Chews vs. Real Food
The market for running fuel is extensive, and what works for one runner may not work for another. The best way to find your perfect fit is through experimentation during training.
The Pros and Cons of Common Fuel Sources
| Fuel Type | Pros | Cons |
|---|---|---|
| Energy Gels | Portable, fast-acting, easily absorbed, consistent dosage. | Can cause stomach upset if not taken with enough water, concentrated flavor can be overwhelming, sticky packaging. |
| Energy Chews | Chewing offers a psychological break from running, pre-portioned, slower energy release. | Can require more effort to chew, slower absorption than gels, potentially bulkier to carry than gels. |
| Real Food | Can be gentler on the stomach, offers more flavor variety, includes items like dried fruit, pretzels, or bananas. | Requires more chewing, digestion is slower than engineered fuels, can be harder to carry. |
| Sports Drinks | Replaces both carbohydrates and electrolytes simultaneously, convenient at aid stations. | Can be too concentrated and upset the stomach, may not provide enough calories for longer events. |
Practical Fueling Strategies for Runners
The 30-60 Gram Rule
For runs lasting between 1 and 2.5 hours, most experts recommend consuming 30-60 grams of carbohydrates per hour. For example, this could be one standard energy gel (about 25g) at 30 minutes, and another at 60 minutes. For runs exceeding 2.5 hours, especially at a higher intensity, some athletes can benefit from increasing their intake to 60-90 grams of carbohydrates per hour, but this requires significant gut training.
Practice in Training
Your long runs are the perfect time to test your race-day nutrition strategy. Practice with the exact fuels you plan to use on race day, and at the same intervals. Pay attention to how your stomach feels and whether the fuel seems to provide the boost you need. Just as you don't wear new shoes on race day, you don't experiment with new foods.
Stay Hydrated
Fueling goes hand-in-hand with hydration. Many concentrated gels and chews require water for proper absorption. Dehydration can exacerbate stomach issues and negatively impact performance, regardless of your fuel intake. The goal is to drink small amounts of water or electrolyte drink frequently, typically 5-10 ounces every 15-20 minutes, adjusting for conditions and sweat rate. For longer efforts, an electrolyte drink can help replace the minerals lost through sweat.
The Aftermath: Post-Run Recovery
Refueling doesn't stop when the run is over. To maximize recovery, it's essential to consume a combination of carbohydrates and protein within 30-60 minutes of finishing. This helps replenish depleted glycogen stores and aids in muscle repair. An ideal ratio is approximately 3:1 carbohydrates to protein.
Conclusion: Fuel Smart, Run Strong
Knowing when to refuel during a long run is a critical skill that every endurance runner must master. By starting your fueling strategy early (around 30-45 minutes into your run), consistently consuming carbohydrates (30-60g per hour), and practicing with your chosen fuel during training, you can dramatically improve your performance and finish strong. Remember that fueling needs are highly individual, so listen to your body and adjust your plan as needed to find the strategy that works best for you. Properly fueled runs are more enjoyable and lead to better results. For further reading, explore expert-backed sports nutrition guidelines from organizations like Sports Dietitians Australia.
When to refuel during a long run FAQ
How soon into a long run should I start eating?
You should begin your fueling strategy about 30 to 45 minutes into your long run, especially if it will last longer than 75 minutes. This ensures you supply your body with carbohydrates before your muscle glycogen stores become depleted.
How many carbohydrates do I need per hour during a long run?
For runs lasting between 1 and 2.5 hours, aim for 30-60 grams of carbohydrates per hour. For efforts longer than 2.5 hours, some athletes may benefit from increasing to 60-90 grams per hour, depending on intensity and gut training.
What are some good fuel options for a long run?
Popular options include energy gels, energy chews, and real foods like dried fruit, pretzels, or bananas. Sports drinks can also replace carbs and electrolytes. The best choice depends on your preference and what your stomach can tolerate, so test options during training.
How does hydration affect fueling during a long run?
Proper hydration is essential for your body to effectively process the fuel you consume. Concentrated fuels like gels need water to be absorbed correctly. Frequent, small sips of water or an electrolyte drink are recommended throughout the run.
Is it possible to eat too much during a long run?
Yes, overconsuming carbohydrates can lead to stomach upset and gastrointestinal distress. Finding the right balance of frequent, small doses is better than taking in large quantities at once. Training your gut is key to handling higher fuel intakes.
How can I tell if I'm fueling correctly during my run?
Good fueling results in consistent energy levels and prevents the sudden fatigue known as 'hitting the wall'. If you feel a steady drop in energy or get stomach issues, you may need to adjust your timing, quantity, or type of fuel during your next training session.
Should I fuel differently for a long training run versus a race?
Your fueling strategy for a long training run should mimic your race-day plan. This allows you to practice with your specific fuel and timing to avoid any surprises on race day. The only difference might be a slight increase in intake during a race due to higher intensity.
