How to Optimise Carbohydrate Intake For Endurance Performance
When it comes to fuelling your performance, consuming the right amount of carbohydrates can be challenging and confusing. To make informed decisions, you’ll need to consider the duration of your training, the intensity of it, how well your body absorbs carbohydrates, and the potential for gastrointestinal (GI) distress. In this blog we’re going to talk through all of these using principles from the Engine Nutrition Program, to make sure you stay fuelled for longer!
Common Pitfalls in Carbohydrate Timing
One of the most common mistakes I see among endurance athletes is delaying carbohydrate intake until too late into an event. This can lead to low energy availibility, where the fuel supply simply can’t keep up with your body’s demands. The result? Decreased performance, prolonged recovery time, and a race that doesn't go as planned.
That’s why planning your carbohydrate strategy is crucial. In this article, I’ll walk you through the key principles to help you optimise your carbohydrate intake for longer training sessions, ensuring you’re fuelling your body for success.
Understanding Carbohydrate Absorption: Glucose vs. Fructose
But first we need to think about absorption of carbs. The carbohydrates that fuel your muscles rely on efficient absorption through your intestines. Our bodies have two main pathways to transport carbohydrates: one for glucose and another for fructose. Think of these as two highways directing fuel to your working muscles.
Here’s how they work:
SGLT1 (Glucose Transporter): This transporter moves glucose and galactose. The maximum rate of glucose absorption is about 1g per minute or 60g per hour. Anything beyond this can accumulate in the gut, leading to GI issues.
GLUT5 (Fructose Transporter): Combining glucose with fructose can increase the absorption rate up to 1.26g per minute or 120g per hour. Some athletes may tolerate even higher fructose intake, allowing for a 1:1 glucose-to-fructose ratio to optimise carbohydrate absorption.
Recent research suggests that athletes can absorb up to 70g of glucose per hour, but when paired with fructose, this number can rise to 144g per hour. However, achieving these higher intake levels requires gut training and consistent trialing during training sessions.
Carbohydrate Intake Based on Training Duration
Carbohydrates can enhance performance across all exercise durations, but the right approach depends on the length of your session. Here’s what you need to know:
30 Minutes to 1 Hour of Training (30-60g per hour)
For shorter sessions, there’s no need to ingest carbohydrates mid-workout. A balanced diet that meets your overall calorie needs should be sufficient. However, a small carbohydrate intake or even a carbohydrate mouth rinse could provide performance benefits.
1 to 2.5 Hours of Training (30-120g per hour)
For sessions up to 2.5 hours, consuming at least 20g of carbohydrates per hour can improve performance. Reaching the higher end of the recommendation, around 90g per hour, can significantly benefit performance but requires gut adaptation and trial during training. A mixture of glucose and fructose in a 1:1 ratio is often well-tolerated and can minimize GI issues.
Over 2.5 Hours of Training (60-144g per hour)
For longer endurance efforts, carbohydrate needs will vary based on intensity and duration. At lower intensities, glucose may be redirected to replenish liver glycogen rather than being used immediately for energy. Athletes training for events like marathons, especially those lasting over 5 hours, should experiment to find the right balance of carbohydrate intake that supports performance without causing digestive issues.
Carbohydrate Mouth Rinsing
A carbohydrate mouth rinse involves swishing a carbohydrate-rich drink in your mouth for 5-10 seconds, then spitting it out. While it doesn’t provide direct fuel, it activates oral sugar receptors that can stimulate neurological responses, boosting performance. This is especially useful when there’s not enough time to fully digest carbohydrates or for those who experience discomfort eating close to exercise.
Reactive Hypoglycemia: What You Need to Know
Around 30% of athletes are sensitive to blood sugar fluctuations, which can lead to symptoms of reactive hypoglycemia—low blood sugar that causes light-headedness or even fainting. This condition is influenced by factors such as training intensity, previous meals, hydration, stress, and more.
If you’re prone to reactive hypoglycemia, consider the following strategies:
Avoid fasted training.
Steer clear of quickly absorbed sugars 1-2 hours before exercise.
Use intra-workout carbohydrate drinks.
Assess your training load and stress levels, as hypoglycemia may be a sign of overtraining or high stress.
Key Takeaways for Endurance Athletes
Events lasting less than 2 hours can often be fueled by glycogen stores without the need for additional carbohydrate intake.
For training sessions longer than 2.5 hours, carbohydrate intake is essential to prevent hypoglycemia, maintain high carbohydrate oxidation rates, and boost performance.
Aim for up to 144g of carbohydrates per hour if needed, using a 1:1 ratio of glucose and fructose to minimize GI distress and maximize performance.
By personalizing your carbohydrate strategy based on your training duration, intensity, and individual tolerance, you can fuel your body effectively and push the limits of your performance.
Need Help Fuelling Your Performance?
I’m a performance nutritionist with a Masters in Human Nutrition and registered with the international society of sports nutrition. See how I can help you here.
