Key takeaways
For a marathon of 2 to 3 hours aim for up to about 60 g of carbohydrate per hour, and for longer events up to about 90 g per hour using glucose plus fructose
Train your gut by practising race fuelling on long runs for weeks before the race, never trying a new product on race day
Drink to thirst and replace sodium in long or hot events, because overdrinking is the main cause of dangerous low blood sodium
Running out of carbohydrate is one of the main reasons marathoners "hit the wall". Good fuelling cannot replace training, but it can protect the work you have done. This guide covers how many carbs per hour to take, how to plan gels, when caffeine helps, how much sodium and fluid you need, and how to train your gut for marathons and ultras.
How many carbs per hour for a marathon?
Your muscles and liver store a limited amount of glycogen, enough for roughly 90 minutes to 2 hours of hard running. Taking carbohydrate during the race spares those stores and keeps blood glucose up.
Jeukendrup (2014, Sports Medicine) set out guidance by event duration (later summarised in his own practical guide):
| Event duration | Carbohydrate per hour | Type |
|---|---|---|
| 45 to 75 minutes | Mouth rinse or small amounts | Any |
| 1 to 2 hours | About 30 g | Any |
| 2 to 3 hours | Up to about 60 g | Rapidly used sugars such as glucose, sucrose or maltodextrin |
| Over 2.5 hours | Up to about 90 g | Must be multiple sugars, such as glucose plus fructose |
The upper limits exist because a single sugar such as glucose can be oxidised at only about 60 g per hour. Mixing glucose with fructose uses a second gut transporter, allowing higher absorption. Jeukendrup also notes that targets are absolute (grams per hour, not per kg) and should be lower when intensity is low.
Higher intakes are being tested. In a mountain marathon with about 4,000 m of cumulative slope, Viribay et al. (2020) found that elite runners taking 120 g per hour had lower markers of muscle damage than those taking 60 or 90 g. These were trained runners who had practised high intakes; most recreational runners should start lower.
Marathon fueling plan by finish time
Most gels contain about 20 to 30 g of carbohydrate, so check the label. Example plans:
| Finish time | Hourly target | Example |
|---|---|---|
| Under 3 h | 60 to 90 g | Gel every 20 min from 20 min in, plus sports drink |
| 3 to 4 h | 60 g | Gel every 25 to 30 min, water at each station |
| 4 to 5 h | 60 to 90 g | Gel every 25 min plus sports drink or chews |
| 5 h+ | 60 to 90 g | Gels, chews and sports drink, eat early before fatigue |
Before the race, top up stores with a carbohydrate-focused day or two and a familiar, low-fibre breakfast 2 to 4 hours before the start. Your target pace (estimate it with the VO2max running calculator) also matters: starting too fast burns glycogen faster. See marathon training and VO2max and tapering before a race.
Gels: how to use them
- Take gels with water, not sports drink. Very concentrated carbohydrate without fluid can upset the stomach.
- Start early. Take the first gel within the first 20 to 30 minutes, not when you already feel flat.
- Use a schedule. Set your watch to remind you; thinking gets worse late in a race.
- Use multiple sugars if your target is above about 60 g per hour.
Ultra fueling
Ultras are slower, so you can eat real food: rice cakes, potatoes, bananas, soup and sandwiches alongside gels. The International Society of Sports Nutrition position stand on ultra-marathons (Tiller et al., 2019) recommends about 150 to 400 kcal per hour, including 30 to 50 g of carbohydrate per hour, plus fluid of about 450 to 750 ml per hour. Many trained ultrarunners use more carbohydrate, in line with the 90 g per hour guidance above, once they have trained their gut. Gut problems are very common in ultras: the same position stand notes that most estimates are 30 to 50% of athletes, with much higher rates reported in some 100-mile races.
Eat little and often, alternate sweet and savoury, and keep eating at night, when appetite often fades. For the training side, see the ultra marathon training plan and, for mountain races, the trail running training plan.
Caffeine for marathons and ultras
The International Society of Sports Nutrition position stand (Guest et al., 2021) concluded that caffeine consistently improves performance at 3 to 6 mg per kg of body mass, that minimal effective doses may be as low as 2 mg per kg, and that very high doses such as 9 mg per kg cause more side effects without extra benefit. Aerobic endurance shows the most consistent benefits. The most common timing is about 60 minutes before exercise, and gels, gum and chews also work.
For ultras, Tiller et al. suggest smaller repeat doses of about 50 mg per hour, especially for night running. Test caffeine in training: it can cause stomach upset, jitters and poor sleep. More in our caffeine guide and caffeine and nitrate.
Sodium and fluids
Sweat losses vary hugely between runners and with weather. Drink enough to avoid large deficits, which reduce gut blood flow and performance, but do not overdrink.
The Third International Exercise-Associated Hyponatremia Consensus (Hew-Butler et al., 2015) defined exercise-associated hyponatraemia as a blood sodium below 135 mmol/L during or up to 24 hours after exercise. The main cause, and the cause of all known deaths, is drinking more fluid than you lose. Risk factors include exercise lasting more than 4 hours, slow pace, inexperience and weight gain during the race. Drinking to thirst is the simplest protection.
In hot conditions, Tiller et al. suggest about 300 to 600 mg of sodium per hour for ultrarunners. Salty sweaters and runners racing in heat may need more. See our electrolytes guide and heat training.
Training the gut
The gut adapts to what you ask of it. Jeukendrup (2017) reviewed evidence that gastric emptying, stomach comfort and intestinal carbohydrate absorption all improve with practice, and Costa et al. (2017) found that two weeks of repeated carbohydrate intake during running reduced gut symptoms and carbohydrate malabsorption.
A simple 6-week progression:
| Weeks | Long run target | Notes |
|---|---|---|
| 1 to 2 | 30 to 40 g per hour | Race gels and drink, at easy pace |
| 3 to 4 | 50 to 60 g per hour | Add one session at race pace |
| 5 to 6 | Race target (60 to 90 g per hour) | Full race-day rehearsal, including breakfast |
Use your long runs for this (see long run pace). If you suffer from cramps, nausea or diarrhoea, see runner's stomach and fibre and the endurance gut.
Safety: seek urgent help if you become confused, have a severe headache, vomit repeatedly or feel bloated with swollen hands during or after a long race, as these can be signs of hyponatraemia. People with diabetes, kidney or heart conditions should plan fuelling and fluids with their doctor.
Frequently asked questions
How many carbs per hour for a marathon?
Up to about 60 g per hour for most marathoners racing 2 to 3 hours, which is two to three typical gels an hour. Slower runners racing 4 hours or more can aim higher, up to about 90 g per hour, if they use glucose plus fructose products and have trained their gut.
What is a good marathon fueling plan?
Eat a carbohydrate-rich breakfast 2 to 4 hours before, take a gel just before the start or within the first 30 minutes, then take one every 20 to 30 minutes with water, aiming for your hourly target. Use only products you have practised with.
How should I approach ultra fueling?
Ultras are run at lower intensity, so real food works alongside gels. Guidance for ultramarathons suggests about 150 to 400 kcal per hour including 30 to 50 g of carbohydrate, with trained runners often tolerating 60 to 90 g or more, plus sodium and fluids to thirst.
Should I take caffeine during a marathon?
Caffeine improves endurance performance at about 3 to 6 mg per kg of body mass, usually taken about 60 minutes before, and lower doses may also work. Caffeinated gels during the race are an option. Test it in training first, because it can upset the stomach and disturb sleep.
Sources
- Jeukendrup A. A step towards personalized sports nutrition: carbohydrate intake during exercise. Sports Med, 2014.
- Jeukendrup AE. Training the gut for athletes. Sports Med, 2017.
- Costa RJS, et al. Gut-training: the impact of two weeks repetitive gut-challenge during exercise on gastrointestinal status, glucose availability, fuel kinetics, and running performance. Appl Physiol Nutr Metab, 2017.
- Viribay A, et al. Effects of 120 g/h of carbohydrates intake during a mountain marathon on exercise-induced muscle damage in elite runners. Nutrients, 2020.
- Tiller NB, et al. International Society of Sports Nutrition position stand: nutritional considerations for single-stage ultra-marathon training and racing. J Int Soc Sports Nutr, 2019.
- Guest NS, VanDusseldorp TA, Nelson MT, et al. International Society of Sports Nutrition position stand: caffeine and exercise performance. J Int Soc Sports Nutr, 2021.
- Hew-Butler T, Rosner MH, Fowkes-Godek S, et al. Statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, 2015. Clin J Sport Med, 2015.