First ultramarathon nutrition: how to fuel your first ultra

Written by James Frost, founder of Flaming Phoenix. Updated October 2026.

Quick answer: For a first ultra of 50km to 50 miles, aim for 150 to 300 calories an hour, including 30 to 50g of carbohydrate, and 450 to 750ml of fluid with some salt, starting in the first hour. Those are the International Society of Sports Nutrition's figures. Rehearse the exact food on long runs, and expect to finish a few thousand calories down.

This guide is the race-day plan: how much to eat and drink each hour, a sample plan for a first 50km with every item counted, what to eat before and after, and how to use aid stations. How to train your stomach to cope with all this has its own page, gut training for ultras, and the wider picture across long events is in our ultra-endurance and expedition nutrition guide.

Why do first ultras so often go wrong on food?

Because once a race passes four or five hours, eating becomes as much of the job as running, and most first-timers have only ever fuelled a marathon. A marathon can be run on the glycogen in your muscles plus a few gels. An ultra cannot. If you are still at the marathon stage, my marathon fuelling guide covers that distance.

The numbers from long races are stark. In a study of a 100-mile race summarised in the International Society of Sports Nutrition's 2019 position stand on ultramarathons, finishers took in 4.6 calories per kilogram of body weight per hour and non-finishers 2.5. For a 70kg runner that is about 320 calories an hour against 175, and 66g of carbohydrate an hour against 42. The same paper advises against intakes that stay below 200 calories an hour.

The catch is that your stomach has limits, and they are lower when you are running hard, hot or dehydrated. That is the reason to practise race-day eating in training; the gut training guide sets out how, week by week.

How many calories and carbs do you need per hour?

For races up to about 50 miles, the ISSN suggests 150 to 300 calories an hour, with 30 to 50g of that as carbohydrate and 5 to 10g as protein. The table shows its figures and what they add up to for a first 50km that takes 6.5 hours.

You will see 60 to 90g of carbohydrate an hour quoted widely. That comes from research on shorter, faster events: Asker Jeukendrup's 2017 review on training the gut recommends about 90g an hour, from a mix of glucose and fructose, for exercise lasting two hours or more. The ISSN's ultra authors regard intakes that high as unrealistic for most runners in races over six hours. For a first ultra, a steady 40g an hour that your stomach accepts is worth more than 80g that makes you sick.

You will burn far more than you eat. The Compendium of Physical Activities rates jogging at 7.5 METs and cross-country running at 9.3, and one MET burns about 1 calorie per kilogram per hour. For a 70kg runner over 6.5 hours, that is between 3,413 calories (7.5 x 70 x 6.5) and 4,232 (9.3 x 70 x 6.5). Eating 1,400 of them leaves a deficit of 2,000 to 2,800, which is normal; you eat it back over the next couple of days. Our calculator works out how many calories you burn running an ultra for your own weight and pace.

A sample fuelling plan for a first 50km

Here is one way to hit those numbers in a 50km that takes 6.5 hours, with aid stations at roughly two and four hours. Carbohydrate and calories come from CoFID values (McCance and Widdowson's tables) for the supermarket foods, the BDA's figure of about 50g of carbohydrate in 800ml of isotonic sports drink, and our own label for Phoenix Bars. The banana is a 180g fruit weighed with its skin.

That comes to about 41g of carbohydrate and 221 calories an hour, inside the ISSN ranges, with a little protein from the bar quarters. Start in the first 30 to 45 minutes, before you feel you need anything. One trick borrowed from experienced runners: bag each hour's food separately, so you can see at a glance whether you are behind.

Aid stations decide how much you carry. Centurion Running's kit guidance says its aid stations range from just over 3 to 12 miles apart; The Lap, a 72km loop of Windermere, has six food and drink stations. Carry enough to cover the longest gap with something spare, and find out beforehand what each station serves. Our guide to ultramarathon drop bags and aid stations covers planning them, and the ultra marathon kit list covers the emergency food many races make you carry on top.

When should real food take over from gels?

Usually somewhere after three or four hours, when sweet things start to pall. Early on, while you are running at a decent clip, fast carbohydrate is the easiest to process: drinks, gels, chews and sweets. As the hours go by, most runners want something savoury and salty, and the ISSN notes this preference grows with race length.

Plan for the switch now, so you do not find out at 30km that you cannot face another gel. Carry something salty, something soft and something that needs almost no chewing. Salted crisps, boiled potatoes, soup, flapjack and soft high calorie foods are the usual answers, and our guides to energy gel alternatives and the best foods for ultra running list more. Mark Brooks, who used a Phoenix Bar on the Brecon to Cardiff ultra, described his method: "breaking it up into bite sized pieces and taking it onboard with water or my carb drink."

How much should you drink, and how much salt?

Drink to thirst, which the ISSN calls the most reliable way to avoid drinking too little or too much, and expect that to come to roughly 450 to 750ml an hour. Add sodium: the ISSN suggests 500 to 700mg per litre of fluid, because many commercial drinks carry less, and it warns that runners drinking to thirst can still fall short on salt.

Drinking large amounts of plain water over many hours, while losing salt in sweat, is how some runners end up with dangerously low blood sodium. Salt in your drinks or food and drinking to thirst are the protection. If nausea hits mid-race, our guide can't eat mid-race? nausea and appetite loss explained goes through what to try.

What changes in the heat?

Everything gets harder: appetite drops, sweet food palls sooner and you lose more fluid and salt. The ISSN suggests about 300 to 600mg of sodium an hour when it is above 25°C or more than 60% humid, and links stomach trouble to the drop in gut blood flow that comes with a rising core temperature and dehydration. In a hot race, lean on drinks and small, salty, soft food, and slow down to keep eating. For racing in real desert heat, our Marathon des Sables nutrition guide goes further.

What should you eat before your first ultra?

The night before, eat a familiar meal built around carbohydrate (pasta, rice, potatoes, bread) and keep it low in fibre and fat, which the ISSN flags as risks in the pre-race meal. The British Dietetic Association's sport and exercise fact sheet suggests a low-fat, high-carbohydrate snack or light meal two to three hours before you start; for most races that means getting up early for porridge, toast with jam or a bagel.

In the two or three days before, raise your carbohydrate so your muscles start full; the carb loading calculator gives grams per day for your weight. Nothing on race morning should be new.

What should you eat after the finish?

Something, as soon as your stomach allows: a drink with some salt first, then carbohydrate and protein, then proper meals over the next day or two. Many runners cannot face much straight away, which is fine. Our ultramarathon recovery guide sets out the days that follow.

How do Phoenix Bars fit a first-ultra plan?

Full disclosure: I make these, so weigh this accordingly. Phoenix Bars carry up to 557 calories in only 120g, with up to 66g of carbohydrate and up to 19g of protein. A quarter of a bar is about 130 to 140 calories and 15 to 16.5g of carbohydrate, which is how the plan above uses them: small pieces through the second half, alongside drinks and sweets. At an aid station with hot water, a bar stirred in makes a soft porridge you barely need to chew; high calorie porridge and how to use Phoenix Bars have the method. Six flavours help when one taste starts to grate.

They are not a replacement for drinks and fast carbohydrate early in the race. Nicole Minicucci used them on her first ultra: "I used Phoenix Bars for my first 58km ultra and they worked really well for me." If you are comparing high calorie bars, our round-up of the best energy bars for ultra running sets the main brands side by side.

First ultra nutrition: common questions

How many calories do you burn in an ultramarathon? Roughly 3,400 to 4,200 for a 70kg runner taking 6.5 hours over 50km, using Compendium values of 7.5 METs for jogging and 9.3 for cross-country running. Heavier runners and longer races burn more. You cannot eat that much while running, so a deficit is normal; the ultra running calorie calculator works out your own figure.

Should you use caffeine in your first ultra? Only if you have tried it in training. The ISSN suggests saving it for the later stages, especially at night, in small repeated doses of 1 to 2mg per kilogram of body weight; about 50mg an hour is likely to be well tolerated. For a 70kg runner, that is a dose of 70 to 140mg.

Should you carry all your food or rely on aid stations? Use both. Carry enough to cover the longest gap between stations plus a spare, eat what the stations offer when it suits you, and never rely on a station having one particular food. Many races also make you carry sealed emergency food that you must not eat unless you need it.

How do you avoid hitting the wall in an ultra? Start eating within the first hour and keep going every 20 to 30 minutes, before you feel hungry; by the time you flag, you are already behind. More on why it happens in hitting the wall late in the race.

Do you need to train your stomach for a first ultra? Yes, at least on your last four or five long runs. Eat the exact foods, at the amounts in your plan, at race effort. The gut training guide has a full plan; in one trial, two weeks of daily practice was enough to reduce runners' stomach symptoms.

Sources: ISSN position stand: nutritional considerations for single-stage ultra-marathon training and racing (2019); Jeukendrup, Training the Gut for Athletes, Sports Medicine (2017); British Dietetic Association: sport and exercise nutrition; 2024 Adult Compendium of Physical Activities: running; McCance and Widdowson's Composition of Foods Integrated Dataset; Centurion Running: mandatory gear explained; The Lap: event information.