The Importance of Carbs During Endurance and Ultra-Endurance Exercise
There is much debate about how to fuel during endurance events, but everyone agrees that nutrition is important during endurance and ultra-endurance exercise. Endurance exercise should prioritize three things: fluid, electrolytes, and carbohydrates.
Why are Carbs Important During Endurance Exercise?
Burning carbohydrates or fat to fuel your activity will depend on the intensity of your exercise. Carbohydrates are the preferred fuel for endurance exercise because your body can turn carbohydrates into energy faster and at greater yields than fat.
In general, your stored carbohydrates (glycogen), which are stored in your muscles and liver, will last a couple of hours or longer, depending on how well you loaded before your race or bout of exercise.
When your glycogen stores are depleted, you may experience a significant drop in energy levels, commonly referred to as “hitting the wall.” This can lead to fatigue and a decline in performance. To avoid this, it’s crucial to replenish your carbohydrates before you start and during exercise.
For endurance exercise lasting over an hour, it's not just about what you eat during the activity. It's about preparing your body well in advance. The International Society of Sports Nutrition recommends a baseline carbohydrate intake of 8-12 g/kg of body weight/day, suggesting that you start thinking about this long before you begin your exercise. The lower end of this range might be for anticipated exercise in the 1-3 hour range, with the higher end for exercise >4 hours.
Maximizing your carbohydrate intake while reducing activity can help load your muscles and liver glycogen stores in the days before a long exercise bout.
General Guidelines for Carbohydrate Intake During Endurance Exercise
Exercise less than one hour (5K running race)—forget about it. Nutrient timing isn’t something you should worry about too much. Fuel in the days before, and rehydrate and refuel post-exercise.
For endurance exercise or races longer than one hour, it is wise to refuel during exercise, if possible. The Academy of Nutrition and Dietetics (Academy), Dietitians of Canada (DC), and the American College of Sports Medicine (ACSM) agree that during endurance and ultra-endurance exercise, you should aim for the following:
Exercise > 1 hour – 30-60 grams of carbohydrate/hour
Exercise > 2.5 hours – 60+ grams of carbohydrate/hour as tolerated
What to Remember About Nutrient Timing
As with most nutrient timing recommendations, there are things to remember:
It’s important to practice your race-day nutrition several times before the real thing.
Your body is unique and you may burn energy differently than someone else. Many of the studies on nutrient timing are done on male athletes. Females burn fat and carbohydrates at different rates than males.
Stress can complicate your tolerance to nutrition and hydration during endurance events. Your gastrointestinal system will let you know when something needs to be adjusted in your nutrition plan.
Extreme temperatures can alter the way your body burns energy.
Carbohydrates for fueling come in different forms, such as liquid (sports drinks), gummy, gel, honey, and solid food (raisins or bars). If you’re not sure which one will work for you, experiment with different types.
Fueling with a mixture of glucose and fructose may help your body absorb more carbohydrates than glucose alone.
The Bottom Line on Carbs During Endurance Events
The consensus is not whether you should fuel during endurance exercise but how and when. Recommendations for carb fueling are based on research studies, but they should serve as your guide and starting point for building your own nutrition plan for endurance events. Practice your nutrition to find out what works best for your body to achieve winning results.
Want to level up your nutrition game? Join the Nutrition Group in the Team RWB app to connect with service members from all branches and eras. They share recipes, tips, and information. They also provide support as you work to achieve your fitness goals.
Sarah Pflugradt is a registered dietitian with a specialization in human performance. She is an Air Force vet, a military spouse, and a health promotion professor at American University in Washington D.C. She spends her free time cooking, writing, and watching her 3 kids compete in sports.
