How Many Carbs Can Your Body Process Per Hour During an Ultramarathon? Latest Research Insights

Ultramarathons push the human body to its limits, demanding not only endurance but also smart nutrition strategies. One of the most critical questions for ultramarathon runners is how many carbohydrates their bodies can process per hour to sustain energy and performance. Recent research sheds new light on this topic, offering practical guidance for athletes preparing for these grueling events.

Runner consuming energy gels during an ultramarathon

Why Carbohydrates Matter in Ultramarathons

Carbohydrates serve as the primary fuel source during prolonged endurance activities. When running for hours, the body relies heavily on glucose derived from carbs to maintain muscle function and mental focus. Unlike fats, which provide more energy per gram but burn slower, carbs offer quick energy release, essential during high-intensity efforts or steep climbs.

The challenge is that the body can only absorb and utilize a limited amount of carbohydrates per hour. Consuming too few carbs risks energy depletion and hitting the infamous "wall." Eating too many can cause gastrointestinal distress, slowing you down or forcing you to stop.

Understanding the optimal carbohydrate intake rate helps ultramarathon runners balance energy needs with digestive comfort.

How Many Carbs Can You Absorb Per Hour?

For years, the general guideline was that the human body could absorb about 60 grams of carbohydrates per hour during endurance exercise. This recommendation was based on the absorption rate of glucose through the small intestine.

Recent studies, however, have found that combining different types of carbohydrates can increase this limit. Specifically, using a mix of glucose and fructose allows the body to absorb up to 90 grams or more per hour. This is because glucose and fructose use different transporters in the gut, reducing competition and improving overall absorption.

Key Findings from Recent Research

• Single carbohydrate sources like glucose or maltodextrin max out absorption at about 60 grams per hour.

• Multiple carbohydrate sources (glucose + fructose) can increase absorption to around 90 grams per hour.

• Some elite athletes tolerate up to 105 grams per hour, but this requires careful training and gut adaptation.

• Consuming carbohydrates above these levels often leads to stomach upset, nausea, or diarrhea.

  
  

Practical Tips for Ultramarathon Nutrition

Knowing the numbers is helpful, but applying them during a race requires planning and practice. Here are some tips based on the latest research:

• Use a mix of carbs: Choose energy gels, drinks, or chews that combine glucose and fructose. Many commercial products now include this blend.

• Start early and steady: Begin carb intake within the first 30 minutes of running and continue at regular intervals to avoid energy dips.

• Train your gut: Practice your race-day nutrition during long training runs to improve carbohydrate tolerance and absorption.

• Listen to your body: Adjust intake if you experience digestive discomfort. Sometimes slowing down carb consumption helps.

• Hydrate properly: Carbohydrate absorption depends on adequate fluid intake, so balance carbs with water or electrolyte drinks.

  
  

Examples of Carbohydrate Intake Plans

Here are two sample plans based on body weight and race duration:

| Runner Weight | Race Duration | Carb Intake per Hour | Carb Sources |

|---------------|---------------|---------------------|------------------------------|

| 60 kg | 6 hours | 60 grams | Glucose-based gels and drinks|

| 75 kg | 10 hours | 90 grams | Glucose + fructose blends |

Adjust these plans according to personal tolerance and race conditions.

Aid station with carbohydrate snacks and drinks during an ultramarathon

The Role of Training and Individual Differences

Carbohydrate absorption capacity varies between individuals. Genetics, gut health, and training all influence how well your body processes carbs during long runs. Athletes who consistently train their gut with carbohydrate intake during workouts tend to tolerate higher amounts during races.

Some runners may find they perform best with lower carb intake but more fat adaptation, while others rely heavily on carbs. Experimenting during training is essential to find your ideal balance.

Summary

Ultramarathon runners can absorb about 60 grams of carbohydrates per hour from a single source like glucose. Using a combination of glucose and fructose can increase this to around 90 grams per hour, with some elite athletes tolerating even more. The key is to practice your nutrition strategy during training, use mixed carbohydrate sources, and adjust based on your body's signals.

Fueling smartly with the right amount and type of carbohydrates can help you maintain energy, avoid hitting the wall, and finish strong in your ultramarathon.

Next step: Try incorporating mixed carbohydrate sources into your long runs and monitor how your body responds. This practice will prepare you to optimize your race-day nutrition and improve your ultramarathon performance.