Is Sugar Important for Running? A Runner's Guide to Carbohydrate Fueling

October 18, 2025 •

4 min read

Did you know that a runner's diet often requires more carbohydrates and, consequently, more sugar than the average person's? The real question isn't whether, but when is sugar important for running and how to use it for optimal performance.

Quick Summary

Sugar, primarily in the form of carbohydrates, is vital for fueling runs, replenishing energy stores, and boosting recovery. Proper fueling depends on the type, amount, and timing of carbohydrate intake for different workout intensities.

Key Points

Glycogen is primary fuel: Carbohydrates are stored as glycogen in muscles and the liver, serving as a runner's primary energy source during exercise.
Timing is everything: Simple sugars are important for fast-acting fuel before, during, and immediately after long or intense runs.
Simple sugars for quick energy: Sports drinks, gels, and chews deliver rapid energy to sustain performance during runs lasting over an hour.
Complex carbs for sustained energy: For daily energy and overall health, runners should prioritize complex carbohydrates found in whole grains, fruits, and vegetables.
Practice your fueling strategy: Don't wait until race day to experiment with your nutrition; use training runs to find the right products and timing for your body.
Distinguish between daily and workout needs: While sugar is crucial for performance, excessive added sugar outside of exercise windows is unhealthy. A runner's diet should still focus on whole foods.
Train your gut: Gradually increasing carbohydrate intake during training helps the digestive system adapt, reducing the risk of gastrointestinal issues on race day.

The Fuel Behind the Run: Understanding Glycogen

For a runner, understanding the body's energy system is key to optimizing performance. When you consume carbohydrates, your body breaks them down into glucose, which is then used immediately for energy or stored for later. This stored form of glucose is called glycogen, and it resides primarily in your muscles and liver. For endurance activities like running, glycogen is the body's preferred and most readily available fuel source.

Your muscles and liver have a limited capacity to store glycogen, which is why a proper carbohydrate strategy is essential. When these reserves become depleted, especially during prolonged or high-intensity exercise, runners experience severe fatigue, a phenomenon commonly known as "hitting the wall" or "bonking". Therefore, managing and replenishing your glycogen stores is a cornerstone of effective sports nutrition for runners.

When Is Sugar Important for Running? The Timing Breakdown

Timing is critical when it comes to carbohydrate intake for runners. The right kind of fuel at the right time can significantly impact your performance and recovery.

Pre-Run Fueling: Topping up the tank

For runs over 60 minutes or high-intensity sessions, pre-run fueling helps top up your glycogen stores and maintain blood glucose levels. A light, easily digestible meal or snack containing mostly carbohydrates should be consumed between one to four hours before your run. This avoids digestive discomfort while ensuring adequate energy is available. Opt for options low in fiber and fat, which can delay digestion. For early morning runners with less than an hour, a small amount of simple carbohydrates like a piece of fruit or a sports drink can provide a quick boost.

Intra-Run Fueling: Sustaining the effort

For runs lasting longer than 60-90 minutes, consuming carbohydrates during the workout is necessary to prevent glycogen depletion and delay fatigue. The standard recommendation is to consume 30-60 grams of carbohydrates per hour. For ultra-endurance efforts (over three hours), some athletes can consume up to 90-120 grams per hour with proper gut training. Simple sugars, found in sports drinks, energy gels, and chews, are ideal here because they are rapidly absorbed and converted to energy.

Post-Run Recovery: Replenishing stores

After an intense or long run, your glycogen stores are significantly depleted. The period immediately following exercise, often called the recovery window, is the most effective time to replenish these stores. A combination of carbohydrates and protein (typically a 3:1 or 4:1 ratio) consumed within 30-60 minutes post-run will accelerate glycogen synthesis and aid in muscle repair. Simple sugars are beneficial during this time for their rapid absorption rate. Chocolate milk is a classic and effective recovery drink that naturally fits this ratio.

Simple vs. Complex Carbohydrates: The Runner's Choice

Not all carbohydrates are created equal, and runners benefit from understanding the difference between simple and complex forms. Knowing when to use each can significantly impact your daily energy levels and performance on the road.

Simple Carbohydrates: These are quickly digested and absorbed, providing a fast burst of energy. They are best used right before, during, or immediately after a run when rapid fuel delivery is needed. Common sources include:

Energy gels and chews
Sports drinks
Honey or maple syrup
Ripe bananas
Dried fruit (e.g., raisins, dates)

Complex Carbohydrates: These have longer chains of sugar molecules, taking more time for the body to break down. They provide a slower, more sustained release of energy, making them the ideal foundation for a runner's daily diet. Complex carbs are great for pre-race carb-loading and daily meals. Sources include:

Whole grains (oats, brown rice, quinoa)
Starchy vegetables (potatoes, sweet potatoes)
Legumes (beans, lentils)
Whole-grain pasta and bread

Simple vs. Complex Carbs for Running: A Comparison


Feature	Simple Carbohydrates	Complex Carbohydrates
Digestion Speed	Rapid	Slower
Energy Release	Quick burst	Sustained, steady energy
Best Timing	Immediately before, during, or right after exercise	Daily meals, days leading up to long races
Best For	Fueling during long runs, fast recovery	Maintaining daily energy, carb-loading
Example Sources	Gels, sports drinks, honey, ripe bananas	Oats, whole-grain bread, potatoes, brown rice

The Pitfalls of Excessive Sugar (at the wrong time)

While simple sugars are vital for athletic performance, it is crucial to understand that these recommendations apply to fueling during specific training windows. Consuming high amounts of added sugar outside of these performance windows can lead to negative health outcomes, including weight gain and increased risk for chronic diseases. Unlike whole foods that contain fiber, protein, and other nutrients, many added sugars provide only “empty calories”. For general health, it's recommended to limit added sugars and prioritize nutrient-dense carbohydrate sources like fruits, vegetables, and whole grains.

Training Your Gut to Handle Carbs

For many runners, especially during longer races, consuming large quantities of carbohydrates can lead to gastrointestinal (GI) distress, such as cramping or nausea. The good news is that the gut is a muscle that can be trained to tolerate higher carbohydrate intake. This process, known as gut training, involves gradually increasing the amount of carbohydrates consumed during training runs. Over time, your gut adapts, improving absorption efficiency and reducing the risk of GI issues on race day.

Conclusion

In conclusion, sugar, in the context of carbohydrates, is undeniably important for runners. It is not an enemy to be avoided, but rather a powerful tool to be used strategically. By understanding the distinction between simple and complex carbohydrates and properly timing their intake, runners can effectively manage their glycogen stores to optimize performance, delay fatigue, and accelerate recovery. It's about finding the right balance: relying on complex carbohydrates for daily sustenance and leveraging simple sugars as a concentrated fuel source during and immediately after intense exercise. Just remember to practice your fueling strategy in training to find what works best for your body, ensuring you hit the wall with confidence instead of crashing into it. For more detailed nutrition guidance, consider visiting the Mayo Clinic Health System website.

Frequently Asked Questions

All sugars are carbohydrates, but not all carbohydrates are simple sugars. For runners, the difference lies in digestion speed. Simple carbohydrates (like glucose in sports gels) are broken down quickly for immediate use, while complex carbohydrates (like whole grains) are broken down slowly for sustained energy.

For runs lasting over 60-90 minutes, runners should aim for 30-60 grams of carbohydrates per hour. For longer ultra-endurance efforts, some athletes can consume up to 90-120 grams per hour with proper gut training.

Good sources include sports drinks, energy gels, energy chews, dried fruit, and ripe bananas. These options provide rapidly available carbohydrates to fuel muscles during exercise.

On rest days, it is best to focus on complex carbohydrates and moderate your intake of added sugars. While sugar isn't inherently 'bad,' your body doesn't need the quick energy boost on rest days, and nutrient-dense options are a better choice for overall health.

Carbohydrate loading is a strategy used by endurance athletes to maximize glycogen stores in the muscles and liver before a long race. It typically involves increasing carbohydrate intake over a few days while reducing training intensity.

Yes, some runners prefer whole foods like dried fruit, bananas, or honey instead of manufactured sports nutrition products. These can be just as effective, but you should practice using them during training to ensure they don't cause digestive issues.

A lack of carbohydrates leads to glycogen depletion, which results in fatigue, slower pace, and decreased performance. In the middle of an endurance event, this is famously known as 'bonking' or 'hitting the wall'.