Carbohydrate fuelling for runners: what's being used and what the research says
We report what runners are using and what the research says. We don't recommend taking any supplement. Talk to your GP or a registered sports dietitian before trying one.
Quick answer
Research suggests it does in longer races. In a systematic review, 82% of 61 trials found carbohydrate improved endurance performance, with bigger gains in longer efforts[1]. Published guidance links the amount to event length: a mouth rinse or small amounts for about an hour, rising to about 60 to 90 g an hour in the longest events[2].
- Research
- Strong (proposed)Clearest in efforts of over about 2 hours. Mixed for runs of around an hour.
- Proposed by our editor; not yet confirmed by an expert reviewer.
- WADA status
- Permitted
- Distances in the research
- 800 m–5K: not studied10K–half: limited researchMarathon: studiedUltra: limited research
What is carbohydrate fuelling?
Carbohydrate fuelling means eating carbohydrate-rich food in the days and hours before a race, often called carb loading, and taking carbohydrate during longer races as drinks, gels or food[3].
The Australian Institute of Sport puts sports drinks, gels and chews in Group A of its supplement framework, meaning strong scientific evidence for use in specific situations in sport[4].
Also called: energy gels, sports drinks, carb loading, carbohydrate loading, race fuelling.
Why is carbohydrate fuelling getting attention?
Fuelling is common in marathon running. In a survey of 5,668 marathon runners in China, 57% carb-loaded before races, and more than 90% of those who used supplements used energy gels[5].
Guidance has moved from a single target to amounts that depend on how long the event lasts[2].
How does carbohydrate fuelling work?
The body stores carbohydrate as glycogen, which fuels hard running. Carb loading aims to store enough for the event's fuel needs[3].
In efforts of about an hour, the benefit may come from carbohydrate sensed in the mouth acting on the brain. In efforts of over about two hours, it comes mainly from supplying fuel[1].
Does carbohydrate fuelling improve running performance?
Yes, for longer races. In a systematic review of 61 trials, 82% found carbohydrate improved endurance performance, and the gains grew with the length of the exercise[1]. In a treadmill marathon, runners were about 4 minutes faster drinking a carbohydrate drink than water[6].
800 m to 5K (Not studied)
We found no trials of carbohydrate taken during races this short. The shortest running trial we found was a 1-hour race[7].
10K to half marathon (Limited research)
For efforts of about an hour, a review found that a carbohydrate mouth rinse or small amounts can improve performance[2]. But in 15 women racing for an hour on a track after an 8-hour fast, a mouth rinse made no clear difference[7].
Marathon (Studied)
In a treadmill marathon, 7 trained runners were about 4 minutes faster with a 5.5% carbohydrate drink than with water, and held their pace for longer. A stronger 6.9% drink made no significant difference[6].
At the Copenhagen Marathon, runners with a planned strategy of gels and water, about 60 g of carbohydrate an hour plus some caffeine, finished 4.7% faster than matched runners who fuelled as they chose[8].
Among 257 London Marathon runners, those who ate more than 7 g of carbohydrate per kg of body mass the day before ran faster and held their pace better, though this was an observational study[9].
Ultra (Limited research)
The research is mostly observational. In one 161 km race, finishers took in more carbohydrate an hour than non-finishers, and intakes varied widely between runners[10].
Guidance differs: the ISSN position stand gives 30 to 50 g an hour for ultra-marathons[10], while another review gives about 90 g an hour for ultra-endurance events[2].
The key studies, in order
- 1995Trial7 trained runners, three treadmill marathons: about 4 minutes faster with a 5.5% carbohydrate drink than with water. A 6.9% drink made no significant difference. [6]
- 2011Observational study257 London Marathon runners: those who ate more than 7 g of carbohydrate per kg of body mass the day before ran faster and held their pace better. [9]
- 2014Expert review30-50% of athletes report gut complaints during exercise. Most are mild, but some can be serious; causes are physiological, mechanical or nutritional. [14]
- 2014Non-randomised trial28 non-elite marathon runners in matched pairs: those with a planned gel strategy (about 60 g of carbohydrate an hour, plus some caffeine) finished 4.7% faster than those who chose freely. [8]
- 2014Expert reviewGuidance by event length: a mouth rinse or small amounts for about 1 hour, up to about 60 g an hour for 2-3 hours, and about 90 g an hour of mixed carbohydrate types for ultra-endurance. [2]
- 2014Systematic review61 placebo-controlled studies: 82% found carbohydrate improved performance, with bigger gains in longer exercise. Around 1 hour, the effect may come through the mouth and brain. [1]
- 2017Trial25 endurance runners: two weeks of practising taking carbohydrate while running cut gut symptoms by about 60% and improved a 1-hour distance test, against no change with a placebo. [12]
- 2017Expert reviewThe gut adapts: a high-carbohydrate diet increases the transporters that absorb carbohydrate, and practice can improve stomach comfort, which may reduce gut problems in races. [13]
- 2018Trial15 recreational women runners racing for 1 hour on a track after an 8-hour fast: a carbohydrate mouth rinse made no clear difference to distance covered. [7]
- 2018ConsensusSports foods and supplements can help in specific situations. Contamination is a known anti-doping risk of supplement products. [16]
- 2019Expert reviewRace nutrition for distance runners: carbohydrate-rich eating before the event, and during it from a mouth rinse in shorter races to 75-90 g an hour in the longest, balanced against gut discomfort. [3]
- 2019ConsensusFor ultra-marathon racing: 30-50 g of carbohydrate an hour with some protein, from a variety of foods. Intakes vary widely, and gut training may reduce gut distress. [10]
- 2025Survey5,668 marathon runners surveyed in 2024: 57% carb-loaded before races, more than 90% of supplement users used energy gels, and about half had had gut symptoms while running. [5]
- 2026Expert reviewReview of more than 160 studies: carbohydrate during exercise improves performance, but the authors argue the main benefit is preventing low blood sugar, most of all beyond 2-3 hours. [11]
What the research can't tell us yet
Researchers still disagree on why carbohydrate helps. A 2026 review argues the main benefit is preventing low blood sugar in efforts longer than 2 to 3 hours, and says this matters for how much athletes are told to take[11].
Many of the running studies are small: the treadmill marathon trial had 7 runners[6], and the marathon field study compared 14 matched pairs of runners without describing the allocation as randomised[8].
How is carbohydrate fuelling used in studies?
Published guidance links the amount to the event's length: a mouth rinse or small amounts for about an hour, up to about 60 g an hour for 2 to 3 hours, and about 90 g an hour for ultra-endurance events, which needs a mix of carbohydrate types such as glucose and fructose[2].
The same guidance is given in grams per hour rather than per kg of body mass, and may need to be lower at easier paces[2]. A review of distance runners puts intakes in the longest races at 75 to 90 g an hour[3].
Practice changes what the gut can handle. In a randomised trial, two weeks of taking carbohydrate on training runs cut gut symptoms by about 60%[12], and a high-carbohydrate diet increases the gut's capacity to absorb it[13].
| What studies used | When | Ref. |
|---|---|---|
| A carbohydrate mouth rinse or small amounts of carbohydrate | During exercise lasting about an hour (guidance) | [2] |
| Up to about 60 g of carbohydrate an hour | During exercise lasting 2 to 3 hours (guidance) | [2] |
| About 90 g of carbohydrate an hour, from mixed carbohydrate types | During ultra-endurance events (guidance) | [2] |
| About 60 g of carbohydrate an hour from gels, with water | During a marathon | [8] |
| More than 7 g of carbohydrate per kg of body mass | The day before a marathon (observational) | [9] |
| 30 to 50 g of carbohydrate an hour, with some protein | During ultra-marathons (ISSN guidance) | [10] |
What are the side effects, and who should be careful?
Gut problems are common: 30 to 50% of athletes report them during exercise. Most are mild, but some can be serious[14].
In the survey of marathon runners, about half had had a gut symptom while running, most often bloating, loose stools, stitches and belching[5].
In running, intakes of about 45 g an hour appear well tolerated, while intakes near 90 g an hour appear harder to tolerate[11].
Be careful if
- You often get stomach problems on runs: gut complaints affect 30 to 50% of endurance athletes[14], and practice in training reduced them in one trial[12].
- You're planning a new gel or drink for race day: guidance stresses a race plan that has been practised in training[3].
- You're aiming for very high intakes: in running, amounts near 90 g an hour appear harder to tolerate than about 45 g[11].
Is carbohydrate fuelling allowed in competition?
Carbohydrate is a food and is not on the World Anti-Doping Agency's Prohibited List[15].
The anti-doping risk with any supplement product is contamination: products can contain prohibited substances that aren't on the label, and athletes are responsible for anything found in their sample[16].
Independent quality-assurance schemes, often called batch testing, check supplement products for prohibited substances[16]. WADA says using a product from one of these schemes can reduce, but not eliminate, the risk of an anti-doping violation[15], and the IOC says no product can be guaranteed entirely safe[16].
Myth or evidence?
5 things runners hear about carbohydrate fuelling. Pick an answer to see what the research says.
1.Taking carbohydrate during a marathon can make you faster.
2.The more carbohydrate you take in a race, the faster you'll run.
3.Gut problems are rare in endurance athletes.
Show the answer
Myth. 30 to 50% of athletes report gut complaints during exercise[14].
4.You can train your gut to handle carbohydrate on the run.
Show the answer
Evidence. In a randomised trial, two weeks of practice cut gut symptoms by about 60%[12].
5.A carbohydrate mouth rinse helps in a 1-hour run.
Have you tried carbohydrate fuelling?
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Frequently asked questions
- Does carbohydrate fuelling improve running performance?
- Research suggests it does in longer races: in a systematic review, 82% of 61 trials found a benefit, and the gains grew with the length of the exercise[1].
- How much carbohydrate an hour does published guidance give?
- It depends on the event: a mouth rinse or small amounts for about an hour, up to about 60 g an hour for 2 to 3 hours, and about 90 g an hour for ultra-endurance events[2].
- Does carb loading help in a marathon?
- The evidence points that way. London Marathon runners who ate more than 7 g of carbohydrate per kg the day before ran faster, though that study was observational[9]. A 2026 review describes a classic 1971 study in which some runners finished a 30 km race up to 15 minutes faster after several days of high-carbohydrate eating[11].
- Do runners need carbohydrate during a 10k?
- Guidance gives smaller amounts for shorter races. For efforts of about an hour, guidance is a mouth rinse or small amounts[2], and a trial of a mouth rinse in a 1-hour race found no clear difference[7].
References
- [1]
Stellingwerff T, Cox GR Systematic review: carbohydrate supplementation on exercise performance or capacity of varying durations. Applied Physiology, Nutrition, and Metabolism, 2014.
Systematic review61 placebo-controlled studies: 82% found carbohydrate improved performance, with bigger gains in longer exercise. Around 1 hour, the effect may come through the mouth and brain.
doi.org/10.1139/apnm-2014-0027 - [2]
Jeukendrup A A step towards personalized sports nutrition: carbohydrate intake during exercise. Sports Medicine, 2014.
Expert reviewGuidance by event length: a mouth rinse or small amounts for about 1 hour, up to about 60 g an hour for 2-3 hours, and about 90 g an hour of mixed carbohydrate types for ultra-endurance.
doi.org/10.1007/s40279-014-0148-z - [3]
Burke LM, Jeukendrup AE, Jones AM, Mooses M Contemporary nutrition strategies to optimize performance in distance runners and race walkers. International Journal of Sport Nutrition and Exercise Metabolism, 2019.
Expert reviewRace nutrition for distance runners: carbohydrate-rich eating before the event, and during it from a mouth rinse in shorter races to 75-90 g an hour in the longest, balanced against gut discomfort.
doi.org/10.1123/ijsnem.2019-0004 - [4]
Australian Institute of Sport AIS Sports Supplement Framework: Group A and linked fact sheets. Australian Sports Commission, 2026.
Consensus statementLists sports drinks, gels, confectionery and bars in Group A as sports foods: strong scientific evidence for use in specific situations in sport.
www.ausport.gov.au/ais/nutrition/supplements/group_a - [5]
Chen Y, Zhao X, Li X, et al. Nutritional status and practices among Chinese marathon runners: data from the China marathon nutrition survey (CMNS). Journal of the International Society of Sports Nutrition, 2025.
Survey5,668 marathon runners surveyed in 2024: 57% carb-loaded before races, more than 90% of supplement users used energy gels, and about half had had gut symptoms while running.
doi.org/10.1080/15502783.2025.2533504 - [6]
Tsintzas OK, Williams C, Singh R, et al. Influence of carbohydrate-electrolyte drinks on marathon running performance. European Journal of Applied Physiology and Occupational Physiology, 1995.
Randomised controlled trial7 trained runners, three treadmill marathons: about 4 minutes faster with a 5.5% carbohydrate drink than with water. A 6.9% drink made no significant difference.
doi.org/10.1007/BF00361543 - [7]
Chryssanthopoulos C, Ziaras C, Oosthuyse T, et al. Carbohydrate mouth rinse does not affect performance during a 60-min running race in women. Journal of Sports Sciences, 2018.
Randomised controlled trial15 recreational women runners racing for 1 hour on a track after an 8-hour fast: a carbohydrate mouth rinse made no clear difference to distance covered.
doi.org/10.1080/02640414.2017.1344358 - [8]
Hansen EA, Emanuelsen A, Gertsen RM, Sørensen SSR Improved marathon performance by in-race nutritional strategy intervention. International Journal of Sport Nutrition and Exercise Metabolism, 2014.
Non-randomised trial28 non-elite marathon runners in matched pairs: those with a planned gel strategy (about 60 g of carbohydrate an hour, plus some caffeine) finished 4.7% faster than those who chose freely.
doi.org/10.1123/ijsnem.2013-0130 - [9]
Atkinson G, Taylor CE, Morgan N, et al. Pre-race dietary carbohydrate intake can independently influence sub-elite marathon running performance. International Journal of Sports Medicine, 2011.
Observational study257 London Marathon runners: those who ate more than 7 g of carbohydrate per kg of body mass the day before ran faster and held their pace better.
doi.org/10.1055/s-0031-1273739 - [10]
Tiller NB, Roberts JD, Beasley L, et al. International Society of Sports Nutrition position stand: nutritional considerations for single-stage ultra-marathon training and racing. Journal of the International Society of Sports Nutrition, 2019.
Consensus statementFor ultra-marathon racing: 30-50 g of carbohydrate an hour with some protein, from a variety of foods. Intakes vary widely, and gut training may reduce gut distress.
doi.org/10.1186/s12970-019-0312-9 - [11]
Noakes TD, Prins PJ, Buga A, et al. Carbohydrate ingestion on exercise metabolism and physical performance. Endocrine Reviews, 2026.
Expert reviewReview of more than 160 studies: carbohydrate during exercise improves performance, but the authors argue the main benefit is preventing low blood sugar, most of all beyond 2-3 hours.
doi.org/10.1210/endrev/bnaf038 - [12]
Costa RJS, Miall A, Khoo A, et al. 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, 2017.
Randomised controlled trial25 endurance runners: two weeks of practising taking carbohydrate while running cut gut symptoms by about 60% and improved a 1-hour distance test, against no change with a placebo.
doi.org/10.1139/apnm-2016-0453 - [13]
Jeukendrup AE Training the gut for athletes. Sports Medicine, 2017.
Expert reviewThe gut adapts: a high-carbohydrate diet increases the transporters that absorb carbohydrate, and practice can improve stomach comfort, which may reduce gut problems in races.
doi.org/10.1007/s40279-017-0690-6 - [14]
de Oliveira EP, Burini RC, Jeukendrup A Gastrointestinal complaints during exercise: prevalence, etiology, and nutritional recommendations. Sports Medicine, 2014.
Expert review30-50% of athletes report gut complaints during exercise. Most are mild, but some can be serious; causes are physiological, mechanical or nutritional.
doi.org/10.1007/s40279-014-0153-2 - [15]
World Anti-Doping Agency The Prohibited List. World Anti-Doping Agency, 2026.
RegulatorThe substances and methods prohibited in sport. Carbohydrate, a food, is not on it.
www.wada-ama.org/en/prohibited-list - [16]
Maughan RJ, Burke LM, Dvorak J, et al. IOC consensus statement: dietary supplements and the high-performance athlete. British Journal of Sports Medicine, 2018.
Consensus statementSports foods and supplements can help in specific situations. Contamination is a known anti-doping risk of supplement products.
doi.org/10.1136/bjsports-2018-099027
Who wrote and reviewed this
Written by Grant MacMillan, Editor, RunV. Not yet reviewed by an expert.
Last checked against its references . Next review due . How pages are reviewed · How we grade research
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