Carbohydrate intake during endurance exercise is one of the most important nutritional strategies for sustaining performance and delaying fatigue. For many years, it was believed that the body could absorb a maximum of 60 g of carbohydrates per hour. However, more recent research has shown that this limitation is not as straightforward as once thought. So, does a carbohydrate absorption limit really exist?
Where Did the 60 g Per Hour Limit Come From?
The traditional recommendation of up to 60 g of carbohydrates per hour originated from studies examining the intestinal absorption capacity of glucose. Glucose is primarily absorbed through the intestinal transporter known as SGLT1, which has a limited transport capacity.
When intake exceeds this capacity, some carbohydrates remain in the gastrointestinal tract, increasing the risk of symptoms such as bloating, nausea, and diarrhea. For this reason, it was long believed that consuming more than 60 g per hour would not provide additional performance benefits.
What Has Changed in Recent Research?
Advances in research have shown that different carbohydrates use different transporters in the intestine.
While glucose is absorbed through SGLT1, fructose is primarily absorbed through the GLUT5 transporter. When glucose and fructose are consumed together, the body can utilize multiple absorption pathways simultaneously, significantly increasing the total amount of carbohydrates absorbed and oxidized during exercise.
This discovery paved the way for nutritional strategies that allow carbohydrate intakes above 60 g per hour, especially during long endurance events.
How Much Carbohydrate Can Be Absorbed Today?
Current scientific evidence shows that trained athletes can absorb and utilize amounts well above traditional recommendations.
Recent guidelines suggest:
Exercise Lasting Up to 2 Hours
Between 30 and 60 g of carbohydrates per hour.
Exercise Lasting 2 to 3 Hours
Between 60 and 90 g of carbohydrates per hour.
Exercise Lasting More Than 3 Hours
Up to 90 g of carbohydrates per hour when using combinations of glucose and fructose.
Advanced Strategies
Highly trained athletes with appropriate gut adaptation may tolerate carbohydrate intakes ranging from 100 to 120 g per hour. Some recent studies have even observed higher rates under specific competition conditions.
However, this does not mean every athlete should immediately consume these amounts.
The Gut Can Be Trained Too
Just as muscles and the cardiovascular system adapt to training, the digestive system can also adapt.
The concept known as "gut training" involves practicing the same nutrition strategy during training sessions that will be used in competition. This process promotes physiological adaptations that can improve carbohydrate absorption and gastrointestinal tolerance.
Athletes who regularly train their carbohydrate intake often experience fewer gastrointestinal issues during long events.
Is There a Universal Limit?
The answer is no.
Although physiological limitations related to intestinal transporters exist, the actual limit varies between individuals and depends on several factors, including:
Gut Training
Adapted athletes generally tolerate higher carbohydrate intakes.
Type of Carbohydrate Used
Glucose and fructose combinations allow higher absorption rates than a single carbohydrate source.
Exercise Intensity
Higher exercise intensity can reduce blood flow to the intestine and increase the risk of gastrointestinal discomfort.
Environmental Conditions
Heat, dehydration, and altitude can influence digestive tolerance.
Individual Characteristics
Genetics, gastrointestinal history, and athletic experience also affect carbohydrate absorption capacity.
Practical Application for Endurance Athletes
The idea that there is a strict limit of 60 g of carbohydrates per hour no longer reflects current scientific knowledge. Today, we know that many athletes can absorb and utilize significantly greater amounts, especially when using appropriate carbohydrate combinations and implementing gut training strategies.
However, increasing carbohydrate intake should not be done randomly. The ideal strategy should be developed progressively during training while respecting the athlete’s individual characteristics and the specific demands of their sport.
For long endurance events, the ability to absorb more carbohydrates can provide a meaningful competitive advantage by preserving energy availability and supporting performance through the final stages of competition.
Conclusion
A carbohydrate absorption limit does exist from a physiological perspective, but it is far more flexible than previously believed. With the right combination of carbohydrate sources, appropriate nutritional strategies, and gut training, many athletes can safely exceed the traditional intake limits.
Rather than focusing on a specific number, the goal should be to identify the carbohydrate intake that maximizes energy availability without compromising gastrointestinal comfort, allowing athletes to sustain performance throughout the entire event.
