The Evolution of Carbohydrate Supplementation in Endurance Athletes: From 60g to 120g per Hour

Carbohydrate supplementation has long been recognized as a critical factor influencing endurance performance. Over the years, the approach to carbohydrate intake during prolonged exercise has evolved significantly, driven by scientific research and practical findings. Originally, athletes were advised to consume around 60 grams of glucose per hour to maintain energy levels. However, recent advancements have led to more sophisticated strategies involving a combination of glucose and fructose in higher quantities, with the latest recommendations suggesting up to 120 grams of carbohydrate per hour in a glucose-to-fructose ratio of 1:0.8.

In this article, we’ll explore the progression of carbohydrate supplementation strategies, from the early 60g per hour approach to the more advanced 120g per hour, and discuss why the latter is considered superior for enhancing endurance performance.

The 60g Glucose-Only Strategy

Early Recommendations

For many years, athletes were advised to consume no more than 60 grams of glucose per hour during prolonged exercise. This guideline was based on the understanding that the small intestine can only absorb a certain amount of glucose per hour due to a saturation of the sodium-dependent glucose transporters (SGLT1). At this rate of intake, athletes could effectively maintain blood glucose levels and delay the onset of fatigue, particularly during events lasting more than 90 minutes.

Limitations of Glucose-Only Supplementation

While 60 grams per hour was effective in maintaining performance, it posed limitations. The primary issue was that it did not fully meet the high energy demands of longer-duration or ultra-endurance events, burning over 800 calories (e.g. 200 grams of carbohydrates) per hour. As glucose absorption is capped by the saturation of SGLT1 transporters, excess glucose beyond 60g per hour would accumulate in the gut, potentially leading to gastrointestinal distress (e.g., bloating, cramping).

The Shift to 90g: Glucose and Fructose (1:0.5 Ratio)

The Role of Multiple Transportable Carbohydrates

The next significant advancement in carbohydrate supplementation came with the discovery that combining glucose with fructose could enhance carbohydrate absorption and oxidation rates. Unlike glucose, which is absorbed via the SGLT1 transporter, fructose is absorbed through the GLUT5 transporter. Because these two sugars use different transport mechanisms, they can be consumed together without saturating the same absorption pathway.

Research has shown that when glucose and fructose are consumed in a 1:0.5 ratio, the total rate of carbohydrate oxidation can increase by up to 50% compared to glucose alone [1]. This translates into a potential intake of 90 grams of carbohydrate per hour (60g glucose + 30g fructose), providing athletes with a higher energy supply without overwhelming the gut.

Improved Performance and Reduced Gastrointestinal Issues

The introduction of fructose not only allowed athletes to consume more carbohydrates but also reduced the likelihood of gastrointestinal distress. By balancing the load between glucose and fructose, the gut is less likely to become overwhelmed, resulting in better tolerance and improved endurance performance.

The Latest Advancement: 120g Glucose and Fructose (1:0.8 Ratio)

Increasing Energy Availability

The latest research has pushed the boundaries of carbohydrate intake even further, now recommending up to 120 grams of carbohydrates per hour, with a glucose-to-fructose ratio of 1:0.8. This strategy is based on the same principle of utilizing multiple transportable carbohydrates but with an optimized ratio that allows for even higher carbohydrate absorption rates.

Why 120g is Superior

1. Maximized Carbohydrate Oxidation: By consuming 120 grams of carbohydrates per hour in a 1:0.8 ratio, athletes can achieve peak carbohydrate oxidation rates. This is higher than the rates observed with both glucose-only and the 1:0.5 glucose-to-fructose blends [2]. This increased oxidation rate leads to better energy availability, which is crucial for maintaining performance during prolonged or high-intensity efforts.

   
   

2. Delayed Fatigue: Consuming more carbohydrates per hour helps maintain blood glucose levels and spares muscle glycogen, delaying the onset of fatigue. This is particularly important for athletes competing in events lasting more than two hours, such as Ironman triathlons or ultra-marathons.

   
   

3. Optimized Gut Tolerance: The 1:0.8 ratio is designed to optimize gastrointestinal tolerance by distributing the carbohydrate load across different transporters (SGLT1 and GLUT5). This minimizes the risk of GI distress, which can be a limiting factor when consuming large amounts of carbohydrates.

   
   

4. Enhanced Recovery: The ability to consume more carbohydrates per hour not only improves performance during exercise but also aids in recovery. By sparing muscle glycogen, athletes recover more quickly, allowing them to resume training or competition sooner.

Practical Applications

Who Can Benefit?

 The 120g per hour strategy is most beneficial for endurance athletes participating in events lasting longer than 2–3 hours, such as marathons, triathlons, ultra-endurance running, and cycling races. These athletes require a high and steady energy supply, and the latest carbohydrate supplementation strategy ensures they can meet their energy needs without compromising performance.

Implementation

 Athletes should aim to practice this carbohydrate intake strategy during training sessions to ensure their gut can tolerate the increased amounts. Gradually increasing carbohydrate intake, while using products designed to deliver the 1:0.8 glucose-to-fructose ratio, will help minimize the risk of gastrointestinal issues and maximize performance.

Conclusion

The evolution of carbohydrate supplementation, from 60 grams of glucose per hour to the current recommendation of 120 grams of glucose and fructose in a 1:0.8 ratio, represents a significant advancement in endurance nutrition. Researches have highlighted the superiority of the 1:0.8 glucose-to-fructose ratio for maximizing carbohydrate oxidation, improving gut tolerance, and enhancing performance during prolonged exercise.

By adopting this strategy, endurance athletes can better meet their energy demands, delay fatigue, and ultimately improve their performance in long-duration events.

References

 1. Jeukendrup AE. "Carbohydrate intake during exercise and performance." Nutrition. 2004;20(7-8):669-677.

2. Rowlands DS, Thorburn MS, Thorp RM, Broadbent S, Shi X. "Effect of graded fructose addition to glucose on exogenous carbohydrate oxidation during cycling." Medicine and Science in Sports and Exercise. 2015;47(6):1283-1291.