Race nutrition
How many carbs per hour should you eat during a long run?
The right number is not one number. It scales with how long you are out there, and it depends on a quirk of intestinal biology that decides how much fuel ever reaches your muscles.
Ask ten runners how much they fuel on a long run and you will get ten answers, most of them too low. The good news is that this is one of the best studied questions in sports science, and the modern guidance is refreshingly specific. The amount of carbohydrate you should take is not a fixed personal preference. It scales with the duration of the effort, and it is capped by a piece of biology you can actually train.
This article walks through the intake guidelines by duration, the glucose plus fructose science that raised the ceiling, why your gut is the limiting organ, and the practical gel and drink maths to hit your number on race day.
The guidelines, by duration
The single most useful shift in sports nutrition over the past two decades was moving away from one blanket recommendation towards advice that scales with how long you are running. Jeukendrup (2014) set out the framework that most governing bodies now follow, and it maps neatly onto duration.
Up to roughly 2 hours: 30 to 60 g/hr.
For most marathon paced and long run efforts, 30 to 60 grams of carbohydrate per hour covers the brain and working muscles. A single carbohydrate source, such as the maltodextrin or glucose in a standard gel, is oxidised at rates up to about 60 grams per hour, so one source is enough here.
Beyond 2 to 3 hours: 60 to 90 g/hr.
Once you are running for several hours, higher intake helps, but only if you switch to a blend of carbohydrates. Pushing past 60 grams per hour with glucose alone does not work, for reasons we come to next. The 90 grams per hour ceiling requires a glucose plus fructose mix.
Beyond that sits an emerging frontier. Some elite marathon and ultra endurance athletes now train to tolerate 90 to 120 grams per hour, chasing the last fraction of available energy. This is the bleeding edge, not a starting point. For all but the fastest racers, it offers diminishing returns and a high risk of gut distress. Treat the 90 grams per hour figure as the practical upper bound unless you have a specific reason and a very well trained gut.
Why a single carbohydrate stalls at 60 grams
The reason you cannot simply eat more glucose comes down to plumbing. Glucose is absorbed across the wall of the small intestine by a transporter called SGLT1. That transporter has a finite capacity, and it saturates at roughly 60 grams per hour. Eat glucose faster than that and the surplus does not reach your bloodstream. It sits in the gut, draws water in by osmosis, and leaves you bloated, nauseous, or worse.
Jentjens and Jeukendrup (2004) demonstrated this limit directly. When trained cyclists drank solutions providing up to 1.8 grams of glucose per minute, the amount of that glucose actually burned for fuel plateaued at around 0.8 grams per minute, the equivalent of roughly 48 grams per hour. The extra glucose simply went unused. The bottleneck was not the muscles, which can burn carbohydrate far faster than that. It was the absorptive machinery of the gut.
The glucose plus fructose breakthrough
The elegant solution was to recruit a second door. Fructose is absorbed not by SGLT1 but by a separate transporter, GLUT5. Because the two pathways work independently, combining glucose and fructose lets you push carbohydrate through both at once, bypassing the single transporter ceiling. Jeukendrup (2010) called these blends multiple transportable carbohydrates, and they are the reason the modern guidelines reach 90 grams per hour at all.
In the same series of experiments, Jentjens and Jeukendrup (2004) showed the payoff. When the cyclists drank a combined glucose and fructose solution, peak exogenous carbohydrate oxidation rose to around 1.26 grams per minute, about 55 percent higher than with glucose alone. That is the difference between roughly 48 grams per hour and well over 70 grams per hour of usable fuel, from the same gut.
The ratio matters. A blend of roughly two parts glucose to one part fructose tends to maximise absorption while keeping the drink palatable, which is why most modern high carbohydrate gels and drink mixes advertise a 2:1 ratio on the label. Some newer products use a 1:0.8 ratio to push intake even higher, but 2:1 remains the reliable default for the 60 to 90 grams per hour range.
Does more fuel actually make you faster?
The intake numbers only matter if the carbohydrate translates into performance. Stellingwerff and Cox (2014) pooled 61 performance studies and found that 82 percent reported a meaningful benefit from carbohydrate intake during exercise compared with a placebo. The size of the benefit grew with the duration of the event. The longer you are out there, the more your fuelling decisions decide the outcome.
That fits the physiology. The body stores only enough muscle and liver glycogen for roughly 90 to 120 minutes of hard running. The Burke et al. (2011) consensus on carbohydrates for training and competition frames the goal as maintaining high carbohydrate availability across the whole session, partly through what you eat in the days before and partly through what you take in during it. Your in race fuelling is what stretches a 90 minute tank across a three hour race. Topping up the tank before the gun also matters, which is why we cover carb loading for a marathon separately.
Train the gut, not just the legs
Here is the part most runners skip. The gut is trainable. The same intestine that rebels at 90 grams per hour on an untrained runner can be coached to handle it. Jeukendrup (2017) reviewed the evidence that gastric emptying, intestinal absorption, and even the perception of fullness all adapt when you practise high carbohydrate feeding repeatedly during training.
Costa et al. (2017) put this to a controlled test. Endurance runners who completed a two week gut training protocol, taking 30 grams of a 2:1 glucose to fructose gel every 20 minutes during their runs, ended up with fewer gastrointestinal symptoms, better carbohydrate absorption, and improved running performance compared with a placebo group. The practical message is simple. Do not debut your race day fuelling on race day. Rehearse the exact products, quantities, and timing on your long runs for several weeks beforehand so your gut is ready.
The practical gel and drink maths
Targets are useless without a delivery plan. Most energy gels carry 20 to 25 grams of carbohydrate, most chews around 4 to 5 grams each, and a typical carbohydrate sports drink around 30 grams per 500 ml bottle at six percent concentration. From there the arithmetic is straightforward.
Hitting 60 g/hr.
Roughly three 20 gram gels per hour, or one gel every 20 minutes. Alternatively, two gels plus a 500 ml bottle of sports drink spreads the load and adds fluid. Set a watch alarm so you do not forget, because most fuelling failures are missed feeds, not wrong totals.
Hitting 90 g/hr.
This needs a 2:1 glucose to fructose blend, otherwise you are back at the SGLT1 ceiling. Two high carbohydrate gels at 40 grams each plus a bottle of mix, or a single 90 gram concentrated gel per hour. At this rate the source must be a multiple transportable blend and your gut must be trained.
Two final cautions. Concentrated carbohydrate needs water to be absorbed, so do not let your fuelling plan crowd out your fluid plan. Get the balance right by reading our guide to hydration for runners. And remember that many gels and drinks include caffeine, which has its own performance evidence and its own dosing rules, covered in our piece on caffeine and running performance.
Frequently asked questions
How many carbs per hour should I eat during a long run?
For runs up to about two hours, aim for 30 to 60 grams of carbohydrate per hour. Beyond two hours, raising intake towards 60 to 90 grams per hour helps, but only if you use a glucose plus fructose mix and have trained your gut to handle it. Very high rates of 90 grams or more are mostly relevant to elite ultra endurance racing.
Why is a single carbohydrate capped at around 60 grams per hour?
The gut absorbs glucose through a transporter called SGLT1, which saturates at roughly 60 grams per hour. Eat more glucose than that and the surplus simply sits in your gut, drawing in water and causing bloating or diarrhoea rather than fuelling your muscles. The transporter, not your muscles, is the bottleneck.
How does glucose and fructose let you absorb more carbs?
Fructose uses a different intestinal transporter, GLUT5, which is separate from the SGLT1 pathway used by glucose. Combining the two carbohydrates in roughly a 2:1 glucose to fructose ratio recruits both transporters at once, so total absorption and oxidation can climb to around 90 grams per hour or higher without overwhelming either route.
What is gut training for runners?
Gut training means deliberately practising high carbohydrate feeding during your long runs so the gut adapts. Over a couple of weeks the stomach empties faster, the intestine absorbs more, and symptoms ease. Research shows runners who train their gut tolerate more fuel and perform better than those who only race on it cold.
How many energy gels is 60 grams of carbs per hour?
Most energy gels contain 20 to 25 grams of carbohydrate. So 60 grams per hour is roughly two and a half to three gels each hour, or one gel every 20 to 25 minutes. A carbohydrate sports drink and chews can replace some gels and spread the load more comfortably across the hour.
Related reading: carb loading for a marathon: how to top up your glycogen stores.
References
- Jeukendrup, A. (2014) ‘A step towards personalized sports nutrition: carbohydrate intake during exercise’, Sports Medicine, 44(Suppl 1), pp. 25 to 33. PubMed.
- Jeukendrup, A.E. (2010) ‘Carbohydrate and exercise performance: the role of multiple transportable carbohydrates’, Current Opinion in Clinical Nutrition and Metabolic Care, 13(4), pp. 452 to 457. PubMed.
- Jentjens, R.L.P.G., Moseley, L., Waring, R.H., Harding, L.K. and Jeukendrup, A.E. (2004) ‘Oxidation of combined ingestion of glucose and fructose during exercise’, Journal of Applied Physiology, 96(4), pp. 1277 to 1284. PubMed.
- Stellingwerff, T. and Cox, G.R. (2014) ‘Systematic review: carbohydrate supplementation on exercise performance or capacity of varying durations’, Applied Physiology, Nutrition, and Metabolism, 39(9), pp. 998 to 1011. PubMed.
- Costa, R.J.S., Miall, A., Khoo, A., Rauch, C., Snipe, R., Camões-Costa, V. and Gibson, P. (2017) ‘Gut-training: the impact of two weeks repetitive gut-challenge during exercise on gastrointestinal status, glucose availability, fuel kinetics, and running performance’, Applied Physiology, Nutrition, and Metabolism, 42(5), pp. 547 to 557. PubMed.
- Jeukendrup, A.E. (2017) ‘Training the gut for athletes’, Sports Medicine, 47(Suppl 1), pp. 101 to 110. PubMed.
- Burke, L.M., Hawley, J.A., Wong, S.H.S. and Jeukendrup, A.E. (2011) ‘Carbohydrates for training and competition’, Journal of Sports Sciences, 29(Suppl 1), pp. S17 to S27. DOI.
All citations point to peer reviewed primary sources, consensus statements, or systematic reviews. Page numbers and volume details are presented per Harvard referencing convention.
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