Carbohydrates and Endurance Exercise

Welcome to the latest edition of the Fueling Greatness Newsletter. Each week, I aim to decode the “science to application” of nutrition and related fields to help you optimise your performance, body composition and well-being. Be at the cutting edge of this knowledge, and subscribe to my newsletter.

Introduction:

Welcome to this week’s newsletter, where I will discuss why optimising carbohydrate intake for endurance exercise and athletic performance is essential because Carbs are King if you want to win! Despite decades of research on this topic, much of which I have reviewed with my expert guests on the We Do Science Podcast, new knowledge continues to be generated with the potential to inform personal choices and professional practice.

In this post, inspired by the recent publication on this topic by Pologar and Wallis, I will provide an overview of the key concepts, including the importance of daily carbohydrate intake, pre- and post-exercise nutrition, carbohydrate types and formats, individualising carbohydrate intake, and emerging technologies.

Daily Carbohydrate Intake

Carbohydrate is the primary fuel source for endurance exercise, and adequate carbohydrate intake is essential for maintaining muscle glycogen stores and optimising performance. To ensure sufficient muscle glycogen availability, endurance competition or high-quality intense training should be preceded by daily dietary carbohydrate intakes scaled to the demands of the subsequent exercise. The American College of Sports Medicine recommends that endurance athletes consume 6-10 g/kg/day of carbohydrates, depending on the duration and intensity of their training.

In addition to daily carbohydrate intake, optimising liver and muscle glycogen content in the hours before and hours directly after exercise are essential goals for carbohydrate nutrition. A periodised approach to dietary carbohydrate intake around training will ensure athletes have sufficient fuel to execute the demands of training to maximise training adaptation whilst minimising the potential for adverse health or performance consequences (e.g., through the development of RED-S).

Pre- and Post-Exercise Nutrition

Nutrition strategies that combine glucose and fructose carbohydrate sources appear most beneficial for the enhancement of performance and recovery. Glucose and fructose are absorbed by different transporters in the small intestine, and combining them can increase the rate of carbohydrate absorption and oxidation. Athletes looking to benefit from carbohydrate feeding during exercise can choose from a wide range of readily oxidisable carbohydrate sources, with glucose-fructose blends (including sucrose) affording the greatest flexibility for within-event modulation of carbohydrate intake.

In addition to during exercise, post-exercise carbohydrate intake is also crucial for replenishing muscle glycogen stores and promoting recovery. The optimal timing and amount of post-exercise carbohydrate intake depends on the duration and intensity of the exercise and the athlete's individual needs and goals. The American College of Sports Medicine recommends that endurance athletes consume 1.0-1.2 g/kg/hour of carbohydrates during the first 4 hours of recovery after exercise.

Carbohydrate Types and Formats

For athletes consuming moderate to high doses during exercise lasting over 60 minutes, glucose-fructose blends (including sucrose) are recommended for their ability to enhance performance and recovery. Other carbohydrate types and formats, such as maltodextrin, glucose, and fructose, can also be effective but may provide different flexibility for within-event modulation of carbohydrate intake.

Maltodextrin is a complex carbohydrate that is rapidly absorbed and oxidised, making it a popular choice for endurance athletes. Glucose is a simple carbohydrate that is also rapidly absorbed and oxidised but may cause gastrointestinal distress at high doses. Fructose is a simple carbohydrate that is absorbed more slowly than glucose but can be eroded at a higher rate when combined with glucose.

In addition to the type of carbohydrate, the format of the carbohydrate can also affect its absorption and oxidation. Liquid and gel formats are typically absorbed more rapidly than solid formats, which may benefit athletes during exercise. However, solid formats may be more palatable and provide a greater sense of satiety, which may benefit athletes during recovery.

Individualising Carbohydrate Intake

While dietary carbohydrate intake guidelines for athletes are well established, individualising carbohydrate intake based on an athlete's specific needs and goals is also important. Factors such as body weight, training volume, and exercise intensity can all affect an athlete's carbohydrate needs.

Emerging technologies such as machine learning and continuous glucose monitoring (CGM) may help athletes predict and monitor their glycogen utilisation and blood glucose responses to nutrition and exercise. Machine learning algorithms can analyse published research studies to predict muscle glycogen use during exercise, which may help athletes personalise their exercise-nutrition strategies. CGM devices can give athletes real-time feedback on their blood glucose responses to nutrition and exercise, which may help them optimise their carbohydrate intake and avoid hypoglycaemia or hyperglycaemia.

A periodised approach to carbohydrate intake can also help athletes adjust their carbohydrate intakes based on need and mitigate against any potential for excessive carbohydrate availability to impede training adaptation. A periodised approach involves adjusting carbohydrate intake based on the athlete's training cycle, with higher carbohydrate intakes during periods of high training volume and lower carbohydrate intakes during periods of low training volume.

Conclusion

Optimising carbohydrate intake is crucial for endurance exercise and athletic performance. Daily carbohydrate intake should be scaled to the demands of the subsequent exercise, and a periodised approach to carbohydrate intake can help athletes adjust their carbohydrate intakes based on need. Combining glucose and fructose carbohydrate sources appears to be the most beneficial for performance and recovery, and athletes can choose from a wide range of carbohydrate sources to meet their needs. Emerging technologies such as machine learning and continuous glucose monitoring may also help athletes individualise their carbohydrate intake and optimise their performance.

It is important to note that while carbohydrate intake is essential for endurance exercise and athletic performance, it should not be the sole focus of an athlete's nutrition plan. Adequate protein and fat intake are also important for maintaining muscle mass and supporting overall health. Additionally, athletes should prioritise nutrient-dense whole foods over processed and refined carbohydrates.

Optimising carbohydrate intake is a complex and multifaceted process that requires individualisation and, ideally, a skilled professional sports nutritionist's attention to detail if optimal training adaptations and competition day results are essential.

Take-Home Messages

1. Carbohydrate is the primary fuel source for endurance exercise, and adequate carbohydrate intake is essential for maintaining muscle glycogen stores and optimising performance.

2. Daily carbohydrate intake should be scaled to the demands of the subsequent exercise, with endurance athletes consuming 6-10 g/kg/day of carbohydrate.

3. A periodised approach to carbohydrate intake can help athletes adjust their carbohydrate intakes based on need and mitigate against any potential for excessive carbohydrate availability to impede training adaptation.

4. Combining glucose and fructose carbohydrate sources appears to be the most beneficial for performance and recovery, with glucose-fructose blends (including sucrose) affording the greatest flexibility for within-event modulation of carbohydrate intake.

5. Other carbohydrate types and formats, such as maltodextrin, glucose, and fructose, can also be effective but may not provide the same flexibility for within-event modulation of carbohydrate intake.

6. Liquid and gel formats are typically absorbed more rapidly than solid formats, which may benefit athletes during exercise.

7. Post-exercise carbohydrate intake is important for replenishing muscle glycogen stores and promoting recovery, with endurance athletes consuming 1.0-1.2 g/kg/hour of carbohydrate during the first 4 hours of recovery after exercise.

8. Individualising carbohydrate intake based on an athlete's specific needs and goals is important, with factors such as body weight, training volume, and exercise intensity affecting an athlete's carbohydrate needs.

9. While carbohydrate intake is essential for endurance exercise and athletic performance, it should not be the sole focus of an athlete's nutrition plan. Adequate protein and fat intake are also crucial for maintaining muscle mass and supporting overall health.

10. Athletes should prioritise nutrient-dense whole foods over processed and refined carbohydrates.

That’s it for today! I hope you found this of interest and value.

Have a great week, and see you next week for another edition of Fueling Greatness, in which we will continue to explore key topics in sport and exercise nutrition and unpack the “science-to-application” to help you achieve your performance, body composition and well-being goals.

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Best regards,

Dr Laurent Bannock