Ultra running nutrition for multi-day races

Written by James Frost, founder of Flaming Phoenix and the maker of Phoenix Bars. Updated November 2026.

Quick answer: In a multi-day ultra, aim for 60 to 90g of carbohydrate an hour while you are moving (about 240 to 360 calories), within the American College of Sports Medicine's guidance of up to 90g an hour for events over 2.5 hours, and expect to burn 4,000 to 7,000 calories on a typical race day. Start eating on a timer from the first hour, because appetite usually fades between hours 18 and 30 and often disappears overnight.

UK multi-day ultras add cold, wet, overnight running to that, which makes eating one of the hardest parts of the race. This guide covers how to keep eating through the night sections and the second half, when most runners stop.

In this guide

• Why UK ultra races create a specific nutrition problem
• The calorie maths of a multi-day ultra
• How many grams of carbohydrate an hour to eat
• Why most runners under-fuel in the second half
• Mandatory kit calorie requirements
• What makes food work in UK race conditions
• How Phoenix Bars can be used
• Practical fuelling strategies by race phase
• Frequently asked questions

About this guide

This guide explains the specific nutrition challenges of UK multi-day ultra races and how to build a fuelling strategy that works in cold, wet, overnight conditions where appetite typically collapses.

For broader guidance on ultra-endurance nutrition across all environments, see the Ultra-Endurance and Expedition Nutrition Guide. For guidance on using Phoenix Bars across different situations, see How To Use Phoenix Bars.

I make Phoenix Bars, high calorie bars for situations where calories per gram of pack weight matter, so I have said where they fit and where other food does the job just as well.

Written by James Frost, founder of Flaming Phoenix and the maker of Phoenix Bars. Last reviewed: November 2026.

UK multi-day ultra races are among the most nutritionally demanding events in endurance sport. Not because the distances are the longest or the terrain is the most extreme, but because the combination of cold, wet, overnight running, sleep deprivation, and sustained effort over 24 to 100+ hours creates conditions where eating becomes hard at the exact moment your body needs calories most.

In a desert ultra, heat suppresses appetite but you can eat at camp. In a mountain ultra in the Alps, you move through villages and can buy food. In a UK winter ultra, you are often moving continuously through the night, in rain and wind, carrying everything you need, with checkpoints that may offer little more than water and a warm room. Your nutrition is almost entirely what you carry and what you packed in your drop bag.

The runners who finish strong are almost always the ones who kept eating after everyone around them had stopped.

Why UK ultra races create a specific nutrition problem

UK multi-day ultras combine several factors that individually suppress appetite and together make eating one of the hardest aspects of the race.

Cold and wet conditions. UK races typically run through autumn, winter, and early spring. Rain, wind, and temperatures between -5°C and 10°C are standard. Cold increases calorie expenditure (the body burns energy to stay warm) while simultaneously reducing appetite and making food harder to eat. Wet, cold hands make opening wrappers and handling food physically difficult.

Overnight running. Most UK multi-day ultras involve one or more overnight stages. Running through the night disrupts the hormonal signals that drive appetite. Many runners report being unable to face food between midnight and dawn, which is often the longest stretch without a checkpoint.

Sleep deprivation. By the second or third night of a multi-day race, cumulative sleep deprivation compounds the appetite problem. Nausea, cognitive fog, and a general revulsion toward food are common. This is the point where most DNFs happen, and under-fuelling is almost always a contributing factor.

Sustained low-intensity effort. UK ultras typically involve long stretches of walking, power hiking, and moderate-pace running over rough terrain. This steady-state effort burns roughly 400 to 700 calories per hour but does not feel intense enough to trigger the urgency of fuelling that a road marathon does. Runners drift into a calorie deficit without realising it until the consequences hit.

Limited resupply. Unlike European ultras with well-stocked aid stations, many UK races offer basic checkpoints with water, perhaps soup, and limited hot food. Your primary nutrition source is what you carry in your race vest and what you placed in your drop bag.

The result: calorie needs are very high (4,000 to 7,000+ calories per day depending on pace, terrain, and conditions), but the conditions make consuming those calories progressively harder as the race goes on.

The calorie maths of a multi-day ultra

Here is the arithmetic for a long stage.

A 70kg runner moving over mixed terrain burns roughly 400 to 700 calories per hour of movement, depending on pace, climbing and pack weight, plus about 85 calories an hour while stopped. For a 24-hour stage involving 16 hours of movement, total calorie need is roughly 8,000 to 12,000 calories. Over a multi-day event, the cumulative requirement can exceed 30,000 calories.

Eating 60 to 90g of carbohydrate an hour gives you 240 to 360 calories an hour from carbohydrate, so on-the-move fuelling covers only about half of what you burn while moving. The rest must come from checkpoint stops, camp meals and pre-race loading. The table shows how that plays out on a 24-hour stage.

These are estimates from typical values, not measurements, but the pattern holds: even a runner who hits the top of the carbohydrate range finishes a long stage thousands of calories down.

How many grams of carbohydrate an hour should I eat in an ultra?

Aim for 60 to 90g of carbohydrate an hour while moving. The American College of Sports Medicine's 2016 position stand recommends 30 to 60g an hour for events of 1 to 2.5 hours and up to 90g an hour for anything longer, so 60 to 90g is the working range for an ultra. Intakes near 90g work best when they mix glucose and fructose, which is how many gels and drink mixes are now made.

In a multi-day race, where much of the time is spent walking and your gut is under strain for days, many runners settle nearer 60g. Treat the International Society of Sports Nutrition's 2019 ultra-marathon position stand as the floor: 150 to 400 calories an hour, including 30 to 50g of carbohydrate. If you want to race near 90g, practise it on long training runs for several weeks first, building up 10g or so at a time.

The deficit is unavoidable. No one consumes as many calories as they burn in a multi-day ultra. The goal is to keep the deficit small enough that performance does not collapse. The difference between a manageable deficit and a race-ending one is often just a few hundred calories per stage, which is why the calorie density of the food you carry is worth getting right.

Why most runners under-fuel in the second half

The pattern is predictable and almost universal. Runners eat well in the first 12 to 18 hours. Appetite is present, the novelty of race food has not worn off, and the body is still responding normally to effort.

Somewhere between hours 18 and 30, appetite begins to fade. Sweet foods become repulsive. Gels trigger nausea. The thought of another energy bar is unbearable. This is palate fatigue compounded by physical fatigue, cold, and the onset of sleep deprivation.

From this point, most runners eat less and less even as calorie needs remain constant or increase. The deficit that has been slowly building suddenly accelerates. By the time the consequences appear (sudden weakness, inability to maintain pace on climbs, emotional collapse, shivering that will not stop), the runner is thousands of calories behind and cannot recover the deficit fast enough to continue.

Willpower will not fix this; planning will. That means carrying food that remains palatable and easy to eat when everything else has become impossible, and eating proactively before appetite disappears rather than reactively after it has gone. The best foods for ultra running change as the race goes on, and our list sets them out hour by hour.

Mandatory kit calorie requirements

Most UK ultra races include a mandatory kit list that specifies a minimum calorie reserve. This is typically 500kcal of emergency food per runner, though some races require more.

A single Phoenix Bar (up to 557 calories) covers that standard requirement in one item. For races requiring higher reserves, two bars (up to 1,114 calories) provide substantial emergency food at a total weight of 240g.

One bar does two jobs. First, it simplifies kit preparation: one bar in the race vest satisfies the requirement without needing to combine multiple smaller items. Second, it means your emergency food is something you would actually want to eat in an emergency, not a random collection of gels and sweets assembled to hit a calorie number.

What makes food work in UK race conditions

The requirements for race food in a UK winter ultra are specific and unforgiving.

Does not freeze or harden. Many standard energy bars set hard near freezing. If you cannot bite into it, it is useless. Our guide to the best energy bars for ultra running notes which types set hard in the cold. Food for UK winter racing must remain soft and edible in near-freezing conditions.

Does not require dry hands to open or eat. Wet, cold, gloved hands are the norm. Food that requires tearing a small notch on a gel packet or peeling a tight wrapper is impractical in these conditions.

High calories per gram. Pack weight matters when you are carrying everything for 24+ hours. Higher calorie density means fewer grams for the same calories.

Not excessively sweet. Palate fatigue from sweet foods is one of the primary reasons runners stop eating in the second half. Food with milder, more neutral flavours sustains appetite across longer timeframes than gels and sweet bars.

Steady calories, not just sugar spikes. Food that combines carbohydrate with fat and protein releases its calories over a longer window, so you can hold a steady pace for hours instead of riding the spike and crash of pure sugar.

Versatile in format. Food that can be eaten as a solid bar when moving, broken into pieces for gradual grazing, or made into porridge with water at a checkpoint provides options for different phases of the race and different states of appetite.

How Phoenix Bars can be used

In a UK winter ultra, your food needs to survive rain, cold, mud and 30+ hours of continuous movement. I make Phoenix Bars, so read this section with that in mind. They hold their texture below freezing, when many standard bars become solid blocks. They can be broken into pieces and stored in a race vest pocket for continuous on-the-move eating, or mixed with water at a checkpoint to make porridge in a cup. A single bar meets the standard 500kcal mandatory kit emergency calorie requirement in one item.

The six flavours are mild and not excessively sweet, which means they remain palatable deep into multi-day efforts when sugar fatigue has made gels and sweet bars intolerable.

While moving: Break a bar into pieces and eat them gradually from a race vest pocket. A full bar eaten over 90 minutes gives you up to about 370 calories an hour alongside whatever gels or other nutrition you are using.

At checkpoints: Eat a full bar or half bar alongside whatever hot food is available. You can also stir a bar into water to make a Phoenix Bar porridge in a cup, with up to 557 calories, ready in two minutes. The psychological and physical benefit of hot food during a cold overnight stage is significant.

In drop bags: Pack two to three bars per drop bag. These serve as guaranteed calorie-dense nutrition regardless of what the checkpoint provides. A drop bag with three Phoenix Bars contains up to 1,671 calories of ready-to-eat food.

During the overnight collapse window: Between midnight and dawn, when appetite has disappeared and sweet food triggers nausea, a mild-flavoured bar broken into small pieces is often easier to get down than another gel. Even half a bar (up to about 280 calories) across a four-hour overnight stretch keeps something going in while other eating has stopped.

"I successfully used Phoenix Bars as part of my fuelling strategy for the Winter Spine Challenger South. Reliable, easily eaten and most crucially for me, tasty and palatable especially towards the end of the race where you find it hard to eat. I ate the bars slowly by breaking them down into chunks and consumed a couple every 30 minutes. Crucially for this race where the temperature was around or below freezing, the bars remained soft enough to eat unlike some other food that I had that was too hard to eat!"

"I ate 5 Phoenix Bars during the Spine Race and I thought they were very good. I like the fact that they are so calorie-dense and that they don't freeze easily in the cold."

Full nutritional information and ingredient lists for all six flavours are available on the product page.

Practical fuelling strategies by race phase

Pre-race (24 hours before start). Focus on familiar, carbohydrate-rich meals. Do not try anything new. Mixing a Phoenix Bar with about 250ml of milk on the morning of the start makes a porridge breakfast of over 600 calories.

Hours 0 to 12 (fresh, appetite present). This is when eating is easiest. Establish a rhythm: eat something every 30 to 45 minutes. Use a mix of gels, bars, and real food. Do not rely exclusively on gels even though appetite makes them easy to take. Building a calorie buffer now pays off later.

Hours 12 to 24 (appetite fading, first night). Switch away from pure sugar. Solid, mild food in small pieces often works better than gels here. Break a bar or a sandwich into pieces and eat them steadily. At checkpoints, mix a bar with water to make porridge. Aim to keep eating even as desire to eat fades.

Hours 24+ (deep fatigue, appetite collapsed). Get calories in any form that works. Tiny pieces of a bar, sips of sugary drinks, whatever the checkpoint provides. Do not wait until you feel hungry because the hunger signal may not come. Eat on a schedule: set a timer on your watch if necessary.

Post-race recovery. Your body has a significant calorie deficit to address. Porridge with full-fat milk within 30 minutes of finishing provides both carbohydrate and protein for recovery. Follow with normal meals as appetite returns over the following 24 to 48 hours.

Related guides

• Ultra-Endurance and Expedition Nutrition Guide
• Marathon des Sables Nutrition
• Cycling and Bikepacking Nutrition
• High Altitude Mountaineering Nutrition
• How To Use Phoenix Bars
• Calorie-Dense Foods: What They Are and When They Help
• Dragon's Back Race food
• Marathon des Sables training

Frequently asked questions

How many calories do I need per day in a multi-day ultra?

Most runners burn 4,000 to 7,000 calories on a typical stage day, and 8,000 to 12,000 on a 24-hour push, depending on pace, terrain, conditions and body weight. You will not eat all of this. The goal is to keep the deficit small enough to hold your pace. A realistic on-the-move target is 60 to 90g of carbohydrate an hour (240 to 360 calories), with larger amounts at checkpoints and camp.

How much should I drink in an ultra, and do I need extra salt?

The International Society of Sports Nutrition's 2019 ultra-marathon position stand recommends 450 to 750ml of fluid an hour, about 150 to 250ml every 20 minutes, and says sodium may need to be taken at a higher concentration than most sports drinks provide (above 575mg per litre) to reduce the risk of low blood sodium. In a cold UK race you will usually sit at the lower end, so drink to thirst and keep taking salt with savoury checkpoint food rather than forcing water down.

How many Phoenix Bars should I carry?

For a single 24-hour stage, three to four bars (up to 2,228 calories) provides a substantial calorie base alongside other nutrition. For drop bags, pack two to three bars per bag. A single bar satisfies the standard 500kcal mandatory kit calorie requirement.

Do Phoenix Bars work in cold and wet conditions?

Yes. Phoenix Bars hold their texture and stay edible in sub-zero temperatures, and one customer ate them at -45°C on a South Pole expedition. They don't freeze solid the way many standard bars do, and the first Spine Race review above was written after racing at or below freezing.

What should I eat when I can't face sweet food?

This is the most common reason runners stop eating in the second half of a multi-day race. Go savoury at checkpoints (soup, noodles, salted potatoes, cheese sandwiches), then carry mild, not-too-sweet solid food in small pieces between them. Swapping some gels for a carbohydrate drink also cuts the sweetness while keeping your grams per hour up.

How does this page differ from the Ultra-Endurance Nutrition Guide?

The Ultra-Endurance and Expedition Nutrition Guide covers general principles of calorie-dense nutrition across all endurance contexts. This page is specifically about the demands of UK multi-day ultra races: cold, wet, overnight conditions, limited checkpoints, mandatory kit requirements, and the late-race appetite collapse that defines these events.

Buy Phoenix Bars

If you have any questions about using Phoenix Bars for UK ultra races, contact me directly. I am always happy to help.

James Frost

Founder, Flaming Phoenix

jfrost@flaming-phoenix.co.uk

07990 519422

Sources: American College of Sports Medicine, Academy of Nutrition and Dietetics and Dietitians of Canada, joint position statement on nutrition and athletic performance (2016); Tiller and others, ISSN position stand: nutritional considerations for ultra-marathon training and racing (2019).