How many carbs per hour should you take during a race?

Race fueling (or fuelling) by event length, sport and how well your gut is trained.

Short answer: it depends mostly on how long you'll be going. A widely cited guideline (Jeukendrup, 2014) recommends small amounts of carbohydrate, or even just a carbohydrate mouth rinse, for exercise of about an hour, up to about 60 g per hour for events lasting 2–3 hours, and about 90 g per hour for ultra-endurance events. To absorb more than about 60 g per hour, the carbohydrate needs to be a mix of glucose and fructose.

Plan your fueling in the Nutrition Planner

Carbs per hour by event length

How long you'll be exercising	Guideline (Jeukendrup, 2014)
About 1 hour	A mouth rinse or small amounts of carbohydrate
2–3 hours	Up to about 60 g per hour; a single source such as glucose or maltodextrin is enough
Ultra-endurance	About 90 g per hour, from multiple transportable carbohydrates (glucose and fructose)

The same review notes that the advice doesn't depend on body weight or training status, and may need to be lower when the absolute intensity is low, because you're burning less carbohydrate.

Why glucose plus fructose?

Glucose (and maltodextrin, which is made of glucose) is absorbed from the gut by a transporter called SGLT1, which tops out at roughly 60 g per hour. Fructose uses a different transporter, GLUT5. Taking both together lets more carbohydrate be absorbed and used: a glucose and fructose mix was oxidised at higher rates than glucose alone (Jentjens & Jeukendrup, 2005), and improved endurance performance compared with glucose alone (Currell & Jeukendrup, 2008). That's why many gels and drink mixes combine the two.

Up to about 90 g per hour, the exact ratio matters less, and close blends such as 1:0.8 work well.
At 120 g per hour, a 1:0.8 fructose:maltodextrin blend raised the amount of ingested carbohydrate used compared with 90 g per hour in a 1:2 ratio (Podlogar et al., 2022).
At 120 g per hour, drinks, gels, chews and combinations of them were used about equally well (Hearris et al., 2022), so the form you take it in is up to you.

Running vs cycling

Ingested carbohydrate is used about as well during running as during cycling (Pfeiffer et al., 2011). Gut symptoms, though, were more common during running than during cycling in a controlled comparison: 44% of athletes against 25%, although they were no more severe (Costa et al., 2022). That's why the Nutrition Planner's running presets are more conservative than its cycling ones.

Train your gut

How much carbohydrate you can take without stomach trouble can be trained. Practising your race fueling in long training sessions, and building up the amount gradually, can improve how well you tolerate it (Jeukendrup, 2017). Never try a new amount or a new product for the first time on race day.

What that looks like in practice

Check the labels of what you plan to use, as products differ. For example, with gels containing 25 g of carbohydrate:

60 g per hour is about one gel every 25 minutes.
75 g per hour is three gels an hour, one every 20 minutes.
90 g per hour is easier to reach by combining gels with a carbohydrate drink, so you're not relying on gels alone.

How the Nutrition Planner helps

The Nutrition Planner's Carb Calculator suggests a carb rate and a glucose:fructose ratio for your sport. Its running presets go from 40 to 120 g per hour, swimming from 30 to 90, and cycling from 60 to 120, with 150 g per hour (advanced) and 180 g per hour (experimental) tiers for athletes who have trained their gut for them. It then works out how many of each gel, chew or drink mix to carry to hit your targets, and checks each bottle's carbohydrate concentration and osmolarity. See the Nutrition Planner guide for how to use it.

References

Jeukendrup A. A step towards personalized sports nutrition: carbohydrate intake during exercise. Sports Med. 2014. PubMed
Jentjens RL, Jeukendrup AE. High rates of exogenous carbohydrate oxidation from a mixture of glucose and fructose ingested during prolonged cycling exercise. Br J Nutr. 2005. PubMed
Currell K, Jeukendrup AE. Superior endurance performance with ingestion of multiple transportable carbohydrates. Med Sci Sports Exerc. 2008. PubMed
Podlogar T, Bokal Š, Cirnski S, Wallis GA. Increased exogenous but unaltered endogenous carbohydrate oxidation with combined fructose-maltodextrin ingested at 120 g/h versus 90 g/h at different ratios. Eur J Appl Physiol. 2022. PubMed
Hearris MA, et al. ¹³C-glucose-fructose labeling reveals comparable exogenous CHO oxidation during exercise when consuming 120 g/h in fluid, gel, jelly chew, or coingestion. J Appl Physiol. 2022. PubMed
Pfeiffer B, et al. Carbohydrate oxidation from a drink during running compared with cycling exercise. Med Sci Sports Exerc. 2011. PubMed
Costa RJS, et al. The impact of exercise modality on exercise-induced gastrointestinal syndrome and associated gastrointestinal symptoms. J Sci Med Sport. 2022. PubMed
Jeukendrup AE. Training the gut for athletes. Sports Med. 2017. PubMed
Fuchs CJ, et al. Fructose co-ingestion to increase carbohydrate availability in athletes. J Physiol. 2019. PubMed

More from the guide

RunTK's tools are for planning and education. They aren't medical advice, and the right numbers for you depend on your health, experience and goals.