The Science Behind Carbs and Running
Carbohydrates are a runner's most important fuel source. When consumed, the body breaks them down into glucose, which is then used for immediate energy or stored in the muscles and liver as glycogen. During moderate- to high-intensity exercise, the body relies heavily on these glycogen stores to power muscle contractions. The total amount of glycogen a runner can store is limited, typically providing enough energy for about 90 minutes of continuous, intense activity.
When glycogen stores are depleted, performance declines significantly. This is the physiological phenomenon known as "hitting the wall". At this point, the body must switch to less efficient fat reserves for energy, causing a noticeable drop in pace and a surge in perceived effort. Therefore, maintaining adequate glycogen levels through proper nutrition is non-negotiable for serious runners aiming to perform at their best and complete longer distances.
Simple vs. Complex Carbohydrates
Not all carbohydrates are created equal, and knowing the difference is key to a smart fueling strategy. The primary distinction lies in how quickly the body digests and absorbs them.
Complex Carbohydrates: These are found in whole grains, starchy vegetables, and legumes. They are digested more slowly, providing a steady, sustained release of energy. These are the ideal choice for everyday meals, helping to maintain stable blood sugar levels and consistent energy throughout the day, not just during your run. Examples include brown rice, whole-wheat pasta, oats, and sweet potatoes.
Simple Carbohydrates: These carbs are broken down quickly for rapid absorption and a fast energy boost. Sources include fruits, honey, and processed options like gels and sports drinks. They are most beneficial immediately before, during, or right after a workout when your body needs readily available fuel to top off stores or accelerate recovery.
Optimizing Your Intake: Timing and Strategy
Daily Intake for Runners
Your daily carbohydrate needs fluctuate based on your training volume and intensity. A runner doing light, low-intensity exercise for less than an hour per day may need 3–5 grams of carbohydrates per kilogram of body weight. For those training 1–3 hours daily at moderate to high intensity, this increases to 6–10 grams per kilogram. For example, a 68kg (150lb) runner training intensely would need 408–680 grams of carbohydrates per day. Spreading this intake throughout the day is the most effective way to meet these demands and avoid feeling uncomfortably full.
The Art of Carb-Loading
For races or long runs lasting over 90 minutes, carb-loading becomes a critical strategy. This involves significantly increasing your carb intake while tapering your training in the 36 to 48 hours leading up to the event. During this period, you should aim for 10–12 grams of carbs per kilogram of body weight per day. To minimize the risk of gastrointestinal issues, it is recommended to focus on low-fiber, easily digestible sources like white rice, white pasta, and peeled potatoes. It is also common to see a slight increase in body weight during this time, which is due to extra water stored with glycogen—a sign you've loaded correctly.
Mid-Run Fueling Strategies
Once your run extends beyond 60–90 minutes, your body will begin to deplete its glycogen stores. To prevent this, consuming 30–60 grams of simple carbohydrates per hour is recommended. For ultra-endurance events lasting over 2.5–3 hours, this amount can increase to 90 grams per hour. Gels, sports drinks, chews, or bananas are common and effective options for this purpose. It is vital to practice your mid-run fueling during training to teach your gut to absorb these carbohydrates efficiently and avoid discomfort.
Post-Run Recovery
To kickstart the recovery process and replenish glycogen stores, consuming a combination of carbohydrates and protein is key. Aim for a 3:1 or 4:1 carb-to-protein ratio within 30–60 minutes of finishing your run, when your muscles are most receptive to storing glycogen. This helps repair muscle tissue and prepares you for your next training session. Chocolate milk, a turkey sandwich, or yogurt with fruit are all excellent recovery options.
High-Carb vs. Low-Carb Diets: A Comparison
| Feature | High-Carb Diet for Runners | Low-Carb Diet (e.g., Keto) for Runners | |
|---|---|---|---|
| Primary Fuel | Glycogen (stored carbs) | Fat (less efficient fuel source) | |
| Performance Impact | Supports high-intensity efforts and endurance, delays fatigue. | Impairs high-intensity performance; reduces running economy. | |
| Recovery | Faster recovery, optimal glycogen replenishment. | Can lead to slower recovery and increased fatigue. | |
| Best For | Competitive and recreational runners aiming for optimal performance and recovery. | Some low-intensity, ultra-endurance athletes or those prioritizing fat loss over performance. | |
| Caveats | Requires diligent fueling to meet high carbohydrate demands. | Not recommended for most competitive runners due to performance drawbacks. |
Conclusion
For the vast majority of runners, the answer to "Should you eat more carbs?" is a resounding yes. Carbohydrates are the cornerstone of a runner's diet, providing the essential fuel for performance, endurance, and recovery. The specific amount and type of carbs should be tailored to your training intensity and duration, with complex carbs forming the foundation of your daily diet and simple carbs strategically used around runs. Low-carb diets are generally not suitable for competitive runners due to their detrimental effect on performance and recovery. By embracing a carbohydrate-forward approach to fueling and paying attention to timing, you can power your runs, delay fatigue, and achieve your running goals. As always, listen to your body and refine your fueling strategy during training. For further guidance on sports nutrition recommendations, consider consulting authoritative sources like the American College of Sports Medicine.
