Breaking Change in the Science of Ultramarathon Fueling
If you've been following ultramarathon nutrition guidelines from just a few years ago, prepare to throw out the playbook. Recent research from elite competitions, including studies from the 24-h World Championships and the 2022 Seville Marathon, is revealing that top performers are consuming far more carbohydrates than previously thought possible, with stunning results.
The paradigm shift? Elite ultramarathon runners are now successfully consuming 60-120 grams of carbohydrates per hour during races, significantly exceeding the traditional 30-60g recommendations that dominated sports nutrition for decades.
What the Latest Research Shows
Elite Performance Data from the 24-Hour World Championships
A landmark study analyzing 12 elite French national team members during the 24-hour ultramarathon World Championships revealed eye-opening findings. According to the research published in the Journal of the International Society of Sports Nutrition, these world-class athletes consumed an average of 1,490g of carbohydrates over 24 hours, translating to approximately 62g per hour for those running between 193-272 km.
Sixty-two grams an hour, held for a full day, by athletes covering up to 272 kilometres. Not a peak on a good climb, but a rate sustained across twenty-four hours of running.
Most remarkably, 11 of the 12 finishers exceeded minimum nutritional recommendations, with energy intake positively correlating with race performance. The athletes maintained this unprecedented intake without significant gastrointestinal distress or exercise-associated hyponatremia, two concerns that have historically limited carbohydrate consumption during ultra-endurance events.
Marathon Runners and the 60-90g Sweet Spot
Complementary research from the 2022 Seville Marathon study found that runners who met carbohydrate intake recommendations of 60-90g per hour during competition were significantly more likely to finish in under 180 minutes. However, the study also revealed a concerning gap: most marathon runners consumed only 35 ± 17g/h, well below current recommendations.
That gap is the practical story. The interesting question for most runners is not whether 120g/h is achievable. It is why the median runner is at 35.
The Science Behind High-Carb Fueling
Breaking Through the Oxidation Ceiling
For years, scientists believed the human body could only oxidize about 60g of carbohydrate per hour during exercise, limited by glucose transporter capacity in the intestinal wall. That ceiling was real, and it was also an artefact of how the carbohydrate was being delivered.
Glucose crosses the intestinal wall through the SGLT1 transporter, and SGLT1 saturates. Once it is full, more glucose does not mean more fuel. It means more glucose sitting in your gut, drawing water in, which is the mechanism behind a great deal of race-day GI misery. Fructose uses a different transporter, GLUT5, which is nowhere near saturated at the same time.
Combining the two lifts the ceiling. Studies now show that with multiple transportable carbohydrates, combining glucose sources with fructose at approximately a 2:1 ratio, athletes can achieve oxidation rates of 90g per hour or higher, against roughly 1.0-1.1g per minute for a single source. That is not a marginal gain. It is most of the difference between the old guidance and the new.
According to the International Society of Sports Nutrition Position Stand on ultra-marathon nutrition, current recommendations suggest 30-50g of carbohydrates per hour for ultra-marathons, with the acknowledgment that trained athletes may benefit from higher intakes approaching 60-90g per hour. The position stands are trailing the practice, as they generally do, and the athletes winning these races are not waiting for them.
Gut Training: The Missing Piece
The key to tolerating these carbohydrate loads is progressive gut training. Recent guidelines from the Turkish Journal of Sports Medicine emphasize that athletes must systematically train their gastrointestinal systems to handle high-carbohydrate intake, just as they train their cardiovascular and muscular systems.
The mechanism is the same transporter story. Repeated exposure to carbohydrate during exercise upregulates SGLT1 expression and improves gastric emptying rates, so the ceiling you are working against is not fixed. It is trainable, over weeks, in the same way that anything else is.
A workable protocol:
- Practice eating during all long training runs, not only the ones you think of as rehearsals.
- Increase volume and frequency gradually. This is a progressive overload problem, and the same rules apply: too much too soon produces the symptom you are trying to avoid.
- Simulate race-day fueling specifically on runs of three hours or more. That is where tolerance actually gets tested.
- Work up to your target rate in key sessions rather than attempting it first on race day.
- Keep a fueling journal. Note what went in, when, and what happened. Individual tolerance varies enough that your own record is better evidence than any published number.
- Use identical products and timing in training to those you intend to race with.
Training Phase: Building Your Carb Foundation
Race-day intake sits on top of daily intake, and the daily number moves with training volume. The research suggests ultra-marathon runners should target 5-8g of carbohydrate per kilogram of body weight daily. For a 70kg runner, this translates to 350-560g of daily carbs, significantly higher than general population recommendations.
The latest nutritional strategies review recommends:
- Short training sessions (<1 hour): 5-7g/kg/day
- Moderate sessions (1-3 hours): 7-10g/kg/day
- Extreme training (>4-5 hours): 10-12g/kg/day
Knowing the number is the easy half. What actually delivers it is a separate question: real food against gels, maltodextrin against table sugar, and why the sports drink on the shelf is the worst of the available options. That is covered in why Gatorade is sabotaging your ultramarathon.
Addressing Gastrointestinal Concerns
One of the most significant findings from recent research is that trained athletes can consume these high carbohydrate loads without debilitating GI distress. In the 24-hour World Championship study, while 75% of athletes experienced some GI symptoms, these were transient (lasting only 3.0 ± 0.9 hours) and didn't significantly impair performance.
Read that honestly: three quarters of the field had symptoms. The finding is not that high intake is comfortable, it is that trained guts recover and carry on. Strategies that reduce the burden:
- Progressive gut training during the preparation phase
- Using multiple transportable carbohydrates (glucose + fructose)
- Avoiding high-FODMAP foods during racing
- Maintaining consistent consumption patterns
- Acquainting the gut with all race nutrition during training
The Hydration and Electrolyte Connection
High carbohydrate intake and fluid intake are coupled, because carbohydrate concentration is what determines how fast a solution leaves the stomach. The evidence supports fluid intake in the region of 450-750 mL per hour and sodium at 500-700 mg/L, both increasing in heat.
Those are evidence-based ranges rather than a plan. How to actually split hydration from calories so you are not forced to drink to hit a carbohydrate target is a practical problem, and it is handled in the practical piece.
The Performance Impact
The relationship between carbohydrate intake and performance is now clearly established. The 24-hour World Championship research demonstrated a positive correlation between energy intake and distance covered. Athletes who met or exceeded carbohydrate recommendations consistently outperformed those who didn't.
Individual Variation and Personalization
While these recommendations provide evidence-based targets, the research consistently emphasizes individual variation. Factors affecting optimal carbohydrate intake include:
- Body weight and composition
- Running intensity and pace
- Environmental conditions (temperature, altitude, humidity)
- Individual GI tolerance and training status
- Race distance and duration
- Previous fueling experience
This is why the fueling journal is not busywork. Every number on this page is a population average, and you are running the race as an individual.
Practical Takeaways for Runners
Based on the latest research:
- Increase daily carb intake during training: Target 5-8g/kg body weight, adjusted for training volume
- Start gut training now: Progressively increase carb intake during long training runs
- Test high-intake strategies: Work up to 60-90g per hour during key training sessions, not on race day
- Use multiple carb sources: Combine glucose and fructose in approximately a 2:1 ratio
- Monitor and adjust: Track intake, GI symptoms, and performance to find your own ceiling
The Bottom Line
The ultramarathon nutrition landscape has fundamentally shifted. Elite athletes are sustaining rates that were considered impossible a decade ago, with measurable performance improvements and manageable side effects, and the mechanism is understood well enough that this is not a fashion. It is the new floor.
It is not only for professionals either. With proper gut training, appropriate product selection and individualized planning, recreational ultra-runners can use the same strategies. The gap between the median runner's 35g per hour and a well-trained 70 is a bigger prize than the gap between 90 and 120, and it is available to almost everybody.
Want to implement these strategies? Start with your next long training run. Gradually increase your carbohydrate intake, monitor your body's response, and adjust accordingly. Remember: the gut is trainable, and the performance benefits are real.
