This page turns the 24-hour fueling evidence into numbers you can write on a crew sheet. For the race format itself, start with the 24-hour race guide; for the general question of what ultrarunners eat, see what ultrarunners eat during a race.
The Calorie Math
In a study of intake and expenditure during a 24-hour race, Costa and colleagues followed 25 runners who covered 122–208 km. They spent about 55 MJ (≈13,100 kcal) and ate about 20 MJ (≈4,800 kcal), a gap of roughly 8,400 kcal. They averaged 37 ± 24 g of carbohydrate and 378 ± 164 mL of water per hour. Every runner finished in energy deficit, 90% had ketones in their urine afterwards, and only one met the standard carbohydrate benchmark for endurance exercise.
You can check that against distance. The International Society of Sports Nutrition (ISSN) ultramarathon position stand puts the cost of running at 47.8–71.7 kcal per km; its worked example is a 70 kg runner spending about 9,900 kcal over 161 km.
| Line | Number | Basis |
|---|---|---|
| Spent in a measured 24-hour race | ≈55 MJ ≈ 13,100 kcal | Costa 2014, 25 runners, 122–208 km |
| Eaten in the same race | ≈20 MJ ≈ 4,800 kcal | Costa 2014 |
| Energy cost per km | 47.8–71.7 kcal | ISSN position stand |
| Cost of 160 km | 7,600–11,500 kcal | 160 × 47.8 to 160 × 71.7 |
| Eaten at 250 kcal per hour | 6,000 kcal | 24 × 250 |
| Deficit at 160 km | 1,600–5,500 kcal | Cost minus intake |
So the answer to "how many calories does a 24-hour race burn" is roughly 8,000–13,000 kcal. To estimate your own, multiply your target distance in km by 48–72, or enter your weight, walking and climb in the running calorie calculator. You cannot eat that much, and you do not need to: a deficit of a few thousand kilocalories is normal. The goal is to keep intake steady enough that you do not slow down for lack of fuel.
How Much Carbohydrate per Hour
The ISSN gives broad ultra-racing ranges of 150–400 kcal, 30–50 g carbohydrate and 5–10 g protein per hour. Our tiers below sit inside those ranges. In a 16-runner Western States study, finishers ate more than non-finishers; that is an association, not proof that eating more would have prevented a withdrawal, so never force food through vomiting.
| Tier | Per hour | When to use it |
|---|---|---|
| Bad-stomach hours | About 30 g and 200 kcal | Rather than stopping; the bottom of the ISSN 30–50 g range |
| Our default | 50 g | Top of the ISSN range; what to plan without deliberate gut training |
| Trained gut, racing for distance | 60–75 g | From glucose–fructose products; three elite 100-milers averaged 71 ± 20 g/h (Stellingwerff 2016) |
| Upper end | Up to 90 g | Do not plan it for 24 hours; the ISSN says rates this high may be unrealistic beyond 6 hours |
Rehearse the amount, products and timing in the gut-training guide. The answer on what ultrarunners eat explains how the ranges differ. Do not increase solely to match a table.
Hour-by-Hour Fueling Plan
This is our default plan; rehearse it and adjust the portions to what your stomach accepts. The night band assumes a morning start; shift it for your start time. Band totals use the stated example values and round the whole-race energy total.
| Hours | Carbohydrate per hour | Energy per hour | What it looks like | Band total |
|---|---|---|---|---|
| 0–4 | 50 g | 200–250 kcal | Drink mix and gels, a few bites of banana or rice; no caffeine | 200 g, 900 kcal |
| 4–10 | 40–60 g (plan 50) | 250–275 kcal | Add one solid each hour (half a sandwich, potatoes, rice) and 5–10 g protein; still no caffeine | 300 g, 1,560 kcal |
| 10–18 (night) | 40–50 g (plan 45) | 225–250 kcal | Warm savory food such as rice or potatoes in broth; about 50 mg caffeine per hour | 360 g, 1,920 kcal |
| 18–24 | 30 g; drop to it if your stomach is struggling | About 200 kcal | Whatever stays down: cola, sports drink, gels, soft food | 180 g, 1,200 kcal |
| Whole race | About 43 g average | About 233 kcal average | About 17% more carbohydrate per hour than the measured 24-hour field ate | About 1,040 g, 5,600 kcal |
Scaling up for a trained gut. Run hours 0–10 at 60–75 g per hour and the night at 50–60 g, and keep about 30 g at the end. That raises the total to about 1,180–1,410 g of carbohydrate. Do not plan 90 g per hour for 24 hours.
If you fall behind, go back to the band. Do not double the next hour to catch up; a large bolus is a common way to start vomiting.
Real Food vs Gels
Use either or both according to tolerance. Products are the easiest way to reach 50 g per hour early: the elite 100-mile runners in Stellingwerff's study took 93% of their calories from commercial products. Real food earns its place later, for variety and because, as the ISSN notes, runners prefer savory food as races get longer. Our default is products for most of the carbohydrate through hour 10, then a growing share of real food overnight.
Carbohydrate per Portion
Approximate values; check your own labels.
- Gel: 20–25 g per sachet
- Sports drink at 6%: 30 g per 500 mL
- Cola: about 27 g per 250 mL
- Medium banana: about 27 g
- Boiled potatoes: about 20 g per 100 g
- Cooked white rice: about 28 g per 100 g
- Pretzels: about 24 g per 30 g, with sodium
- Half a jam sandwich: about 20 g
About 50–55 g could come from one gel plus 500 mL of sports drink, or a banana plus 100 g of rice. These are food arithmetic examples, not fluid quotas. Test every item, in these portions, on long training days.
Hydration and Electrolytes
Drink to thirst instead of forcing a quota. The ISSN position stand gives a broad racing reference of 450–750 mL per hour; individual needs vary with conditions and effort. Costa's 24-hour runners averaged 378 mL per hour (9.1 L in total). That is an observation in one group, not a drinking target or proof that the same intake would be sufficient for you.
- Sodium: the ISSN discusses 500–700 mg per litre of fluid and roughly 300–600 mg per hour in hot or humid conditions. These are planning references, not mandatory doses for every runner. Count food and drink together and rehearse tolerance; seek individual advice where medical factors or unusual losses warrant it.
- Body mass: the corrected Hoffman model estimates 1.2–3.5% mass loss while maintaining body-water balance under its assumptions for a roughly 25–30-hour, 161-km mountain ultra. This is not a weight-loss target or a diagnostic threshold. Weight gain can signal excess fluid, but weight change alone cannot diagnose or exclude dehydration or hyponatremia.
- Salt does not cancel overdrinking. The hyponatremia consensus statement identifies drinking beyond losses as the main cause of exercise-associated hyponatremia.
Correction, October 23, 2026: This section now uses the published correction to Hoffman's model and distinguishes research ranges from individual intake or weight-loss targets.
The hydration and sodium guide has the sweat-rate test, the sodium arithmetic and the fluid warning signs; the sweat rate calculator does the test arithmetic for you.
When Your Stomach Shuts Down
At Western States, 96% of runners reported gastrointestinal symptoms, and 35.6% of non-finishers named them as a reason for dropping out, nausea above all (Stuempfle 2015). Heat, pace, concentrated carbohydrate, large boluses and unfamiliar ingredients all contribute (Costa 2017). Mild nausea may improve with lower effort and smaller portions, but forcing intake through worsening symptoms can make matters worse.
- Reduce effort or stop safely and reassess how you feel.
- Try small tolerated portions of familiar food or drink. Do not force a carbohydrate or fluid minimum; a brief pause may be needed.
- Switch texture to the option that has worked in training: sips if solids will not go down, bland bites if sweet drinks will not.
- Resume gradually as symptoms settle; persistent or worsening symptoms need assessment.
Caffeine Strategy
Our default follows the ISSN ultramarathon position stand: none in the first ten hours, then about 50 mg per hour overnight, which it describes as likely to be well tolerated, or small repeat doses of 1–2 mg per kg (70–140 mg at 70 kg) rather than repeated 4–6 mg/kg boluses. Eight night hours at 50 mg add up to 400 mg, so skip doses if you get jittery, and skip caffeine entirely if you are sensitive to it. For scale, three elite 100-mile runners reported 912 ± 322 mg across a whole race (Stellingwerff 2016).
- Use only familiar products with a known dose, and record time and milligrams from coffee, cola, gels and tablets together.
- Plan around sleep opportunities and personal sensitivity. Caffeine can disrupt later sleep and does not replace rest.
- Avoid testing caffeine close to normal bedtime just to imitate race hours.
- Stop further caffeine if it causes adverse effects; persistent palpitations or other concerning symptoms need assessment.
Seek individual advice if medical conditions, pregnancy or medication could change your risk. The sleep strategy guide covers rest and caffeine together.
Night Nutrition
Sweet products may become unappealing later. Prepare familiar alternatives for the hours that actually fall overnight:
- Warm and savory: rice in broth, noodle soup, or salted potatoes, which also carry sodium.
- 45 g per hour: for example 100 g of rice in broth plus 150 mL of cola, or 200 g of salted potatoes plus a few sips of sports drink.
- Protein: 5–10 g per hour from milk, yogurt, or a sandwich with ham or cheese, if it sits well.
- Caffeine: about 50 mg per hour overnight, as above.
Common Mistakes
- No practiced fuel plan: rehearse regular intake early, without treating a particular hourly amount as a compulsory floor.
- Chasing missed calories: doubling the next hour causes more trouble than the missed hour did.
- Adopting high intake untested: practice even moderate amounts; 50 g/h is an example, not a dose guaranteed to suit everyone.
- One texture or flavor: carry sweet, savory, liquid and solid options you have tested.
- Forcing fluid or salt: drink to thirst and do not use salt to compensate for excessive drinking. Confusion, repeated vomiting or worsening symptoms need prompt medical assessment, regardless of weight change.
- Automatic caffeine redosing: a race-hour schedule does not account for cumulative intake, side effects or sleep.
Sources
- Costa, R.J. et al. (2014) — Perturbed energy balance and hydration status in ultra-endurance runners during a 24 h ultra-marathon. British Journal of Nutrition, 112(3), 428–437.
- Tiller, N.B. et al. (2019) — 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, 16(1), 50.
- Stuempfle, K.J. et al. (2011) — Race diet of finishers and non-finishers in a 100 mile (161 km) mountain footrace. Journal of the American College of Nutrition, 30(6), 529–535.
- Stellingwerff, T. (2016) — Competition Nutrition Practices of Elite Ultramarathon Runners. International Journal of Sport Nutrition and Exercise Metabolism, 26(1), 93–99.
- Costa, R.J.S. et al. (2019) — Nutrition for Ultramarathon Running: Trail, Track, and Road. International Journal of Sport Nutrition and Exercise Metabolism, 29(2), 130–140.
- Stuempfle, K.J. & Hoffman, M.D. (2015) — Gastrointestinal distress is common during a 161-km ultramarathon. Journal of Sports Sciences, 33(17), 1814–1821.
- Costa, R.J.S. et al. (2017) — Systematic review: exercise-induced gastrointestinal syndrome-implications for health and intestinal disease. Alimentary Pharmacology & Therapeutics, 46(3), 246–265.
- Hew-Butler, T. et al. (2015) — Statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, 2015. Clinical Journal of Sport Medicine, 25(4), 303–320.
- Hoffman, M.D. et al. (2018) — Considerations in the Use of Body Mass Change to Estimate Change in Hydration Status During a 161-Kilometer Ultramarathon Running Competition. Sports Medicine, 48(2), 243–250.
- Hoffman, M.D., Goulet, E.D.B. & Maughan, R.J. (2018) — Correction to: Considerations in the Use of Body Mass Change to Estimate Change in Hydration Status During a 161-Kilometer Ultramarathon Running Competition. Sports Medicine, 48(12), 2893–2894. Corrected model calculations used above.
- Guest, N.S. et al. (2021) — International society of sports nutrition position stand: caffeine and exercise performance. Journal of the International Society of Sports Nutrition, 18(1), 1.
Frequently Asked Questions
How many calories do you burn in a 24-hour race?
Roughly 8,000–13,000 kcal. Costa's 24-hour race study measured about 55 MJ (≈13,100 kcal) spent by 25 runners covering 122–208 km, against about 20 MJ (≈4,800 kcal) eaten. The ISSN position stand puts the energy cost of running at 47.8–71.7 kcal per km, which is 7,600–11,500 kcal over 160 km. Eating 250 kcal an hour supplies 6,000 kcal, so a deficit of 1,600–5,500 kcal is normal and does not need to be closed.
How many grams of carbohydrate per hour should you eat in a 24-hour race?
Our default is 50 g per hour, the top of the ISSN ultramarathon range of 30–50 g. With a trained gut and glucose–fructose products, 60–75 g is realistic; three elite 100-mile runners averaged 71 g an hour. On bad-stomach hours, drop to about 30 g and 200 kcal rather than stopping, and do not plan 90 g an hour for 24 hours: the ISSN calls rates that high likely unrealistic beyond six hours.
Should I eat gels or real food during a 24-hour race?
Both. Drink mix and gels are the easiest way to hit 50 g per hour in the first hours; elite 100-mile runners took 93% of their calories from commercial products. From hour 4, add one solid portion and 5–10 g of protein each hour, and switch to warm savory food overnight, when runners tend to prefer savory food.
What do you do when nothing sounds good during an ultra?
Reduce effort and try small portions of familiar food or drink if tolerated. Pause intake briefly if necessary rather than forcing a numerical minimum, and reassess symptoms. Resume gradually as nausea settles. Repeated vomiting or being unable to keep fluid down means race medical staff, not more food.
How much should I drink per hour in a 24-hour race?
Drink to thirst instead of forcing a quota; for most runners that lands within the ISSN's 450–750 mL an hour, less on cool nights. Our sodium default is the ISSN's 500–700 mg per litre of fluid, counting food and drink. Gaining weight during the race is a warning sign of overdrinking, and salt does not make overdrinking safe; confusion or repeated vomiting need race medical staff.