How many carbs per hour in a marathon?

The trial

Only one randomized trial has tested a fuelling plan in recreational marathoners during a real race (Hansen and colleagues, 2014). At the Copenhagen Marathon, 28 runners were paired up by ability. One runner in each pair followed a scheduled plan of gels giving about 60 g of carbohydrate per hour, together with water and about 90 mg of caffeine per hour. The other chose their own fuelling.

The planned group finished in an average of 218.5 minutes, against 229.4 minutes for the self-fuelling group. That is about 11 minutes, or 5%, faster. Finish times ranged from 2:48 to 4:34, so this was not a study of elite runners. Four-hour marathoners were included.

Most runners eat about half that

Knowing the guideline doesn’t mean following it.

• In 160 Spanish marathoners, carbohydrate intake during the race averaged 35 g per hour (Jiménez-Alfageme and colleagues, 2025).
• When researchers weighed runners’ gels and drinks before and after a race, the runners had planned to take 25.9 g per hour and actually took 21.7 g (Lanpir and colleagues, 2025).
• In a survey of endurance athletes, only 36% reached 60–90 g per hour. Knowing the recommendation did not predict whether they reached it (Sampson and colleagues, 2024).

For most recreational runners, simply getting to about 60 g an hour is the step that matters. The debate about 90 or 120 g an hour is a question for a small group of fast, gut-trained runners.

Why grams per hour, not per kilo

Carbohydrate recommendations during exercise are given in absolute grams per hour, not per kilo of body weight. The limit is mainly how fast the gut can absorb sugar, which doesn’t scale with body size (Jeukendrup, 2014). The international athletics consensus spans from small amounts in shorter events up to 75–90 g per hour in the longest races (Burke and colleagues, 2019). Slower runners work at a lower absolute intensity and burn carbohydrate more slowly, so the lower end of the range can be enough for them.

Mixing glucose and fructose

Glucose and fructose are absorbed through different transporters in the gut. Above about 60 g an hour, a mix of the two lets you absorb more with fewer stomach problems. Recent work favours a ratio of about 1 part glucose to 0.8 parts fructose over the older 2:1 (Podlogar and Wallis, 2022). Below 60 g an hour, any standard gel or sports drink works.

What about 90–120 g an hour?

Very high intakes are being tested in elite runners, but the evidence is thin:

• In eight elite men, 120 g an hour gave a 2.6% lower oxygen cost of running than 60 g. Stomach problems were highest at the top dose, and there was no performance test (Ravikanti and colleagues, 2025).
• In highly trained runners, 90 g an hour with gut training gave no better 35 km result than lower intakes (King and colleagues, 2022).

Unless you are fast and have trained your gut for it over weeks, more than 90 g an hour is unlikely to help.

Your gut can be trained

Stomach problems are the main reason runners eat too little. The gut adapts to regular carbohydrate during running:

• Two weeks of daily one-hour runs taking about 90 g of carbohydrate an hour cut stomach symptoms by roughly 60% and halved malabsorption (Costa and colleagues, 2017; Miall and colleagues, 2018).
• A review of eight small trials found an average 47% drop in gut discomfort after gut training (Martinez and colleagues, 2023).

A practical approach is to start 6–10 weeks before the race, fuel every long run and one or two midweek runs, and raise the dose by 10–15 g an hour each week. Hold the dose if your stomach complains, and step back if it gets bad. Rehearse the full plan, including breakfast, in at least two long runs.

A note on drinking

The Copenhagen trial also scheduled water. Drinking a fixed amount is not the right lesson to take from it. For slower runners, drinking too much is the bigger danger, because it can lower blood sodium to dangerous levels. Drink to thirst, and get your carbohydrate from gels or a measured sports drink rather than forcing fluid.

What we don’t know

• It is one trial with 28 runners, from 2014.
• The plan combined carbohydrate, caffeine and water, so the trial can’t say how much of the 11 minutes came from carbohydrate alone.
• Higher targets for amateurs are unproven. A field trial comparing 80 and 50 g an hour in amateur marathoners exists only as a preprint, and its first and second versions disagree on whether the difference was significant.
• Gut-training studies are small and mostly in men.

Sources

• Hansen et al. (2014). Planned vs self-chosen fuelling in the Copenhagen Marathon.
• Jiménez-Alfageme et al. (2025). Carbohydrate intake in 160 marathon runners.
• Lanpir et al. (2025). Planned vs actual carbohydrate intake in marathoners.
• Sampson et al. (2024). Carbohydrate intake practices of endurance athletes.
• Jeukendrup (2014). A step towards personalized sports nutrition: carbohydrate intake during exercise.
• Burke et al. (2019). International athletics consensus on nutrition.
• Podlogar and Wallis (2022). Glucose–fructose ratios for high carbohydrate intakes.
• Ravikanti et al. (2025). 120 vs 60 g/h carbohydrate in elite runners.
• King et al. (2022). High carbohydrate intake and gut training in highly trained runners.
• Costa et al. (2017). Gut training and gastrointestinal symptoms.
• Miall et al. (2018). Two weeks of gut training in endurance runners.
• Martinez et al. (2023). Systematic review of gut training.