Ultra-endurance and expedition nutrition guide

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

Quick answer: Ultra-endurance events and expeditions burn roughly 4,000 to 8,000 calories a day, but most people can only take in about 200 to 400 calories an hour while moving, so the aim is to keep the daily deficit small rather than close it. Eat little and often by the clock, from food at 4.5 calories per gram or more, and carry a mild backup food for when appetite fails.

Ultra-endurance events and expeditions create a problem that most general nutrition advice does not address: calorie needs are very high, but appetite, time, carrying capacity, and food tolerance are all limited. The people who cope best are rarely the biggest eaters. They are the steadiest ones, eating little and often from food that gives the most calories for the least weight, bulk and effort.

This guide covers the principles of nutrition for ultra-endurance events, multi-day races, long expeditions, trekking, mountaineering, and remote travel where maintaining adequate calorie intake is difficult. It is built around feeding yourself in hard conditions, not on laboratory recommendations that assume you have a kitchen, a schedule and a working appetite.

For situation-specific guidance, see our dedicated guides to UK multi-day ultra race nutrition, Marathon des Sables nutrition, polar expedition nutrition, high-altitude mountaineering nutrition, and military field nutrition.

Why does nutrition decide ultra-endurance outcomes?

In a road marathon, nutrition matters but fitness dominates. In a multi-day ultra or an expedition lasting weeks, nutrition is often what decides whether you finish, and in what condition.

The reason is cumulative calorie deficit. A runner covering 50 miles per day over mixed terrain burns roughly 5,000 to 8,000 calories per day. An expedition member hauling a pulk across polar ice or trekking at altitude may burn 5,000 to 7,000 calories per day. Even with aggressive fuelling, most people can only absorb 200 to 400 calories per hour while active. The deficit starts on day one and grows every day after.

A large calorie deficit brings slower thinking, reduced physical output, slower recovery between stages, a higher risk of injury and, in extreme cases, hypothermia, because the body cannot generate enough heat without fuel. Those effects build quietly, which is why the deficit is easy to ignore until it ends a race.

The goal of an ultra-endurance nutrition plan is not to eliminate the deficit, which is practically impossible in most events. The goal is to minimise it enough that you retain the physical capacity, cognitive function, and morale to keep going. The difference between a manageable deficit and a race-ending one is often a few hundred calories a day. That is where calorie density comes in: from high calorie bars at about 4.5 calories per gram, an extra 300 calories weighs only 67g.

Why is calorie density the defining metric?

Calorie density (the number of calories a food provides per gram) is the most important number in expedition and ultra-endurance nutrition. It determines how many calories you can carry for a given pack weight, and it determines how much you need to eat to hit a calorie target.

Here is how common endurance foods compare. Figures are approximate, from typical UK label values, and grams are rounded to the nearest 5.

Water is what drags most foods down: fruit and cooked rice and pasta are mostly water, and many gels carry a lot of it too, which is why they weigh so much for their calories. Standard energy bars vary widely (our ranking of the best energy bars for expeditions compares them bar by bar), and the densest single items you can eat on the move are nuts, chocolate and dense high-calorie bars at about 4.5 calories per gram or more.

If you need 3,000 supplementary calories per day on a five-day self-supported race, carrying food at 2.0 calories per gram means 1,500g of food per day, or 7.5kg for the event. Carrying food at 4.5 calories per gram means 667g per day, or 3.3kg for the event. That 4.2kg difference is about the weight of four litres of water.

For a detailed explanation of calorie density and how it applies across different situations, see our guide to calorie-dense foods.

The five nutrition challenges of ultra-endurance

Ultra-endurance athletes and expedition participants face five problems that feed into each other over time.

Appetite suppression. Prolonged exertion, heat, cold, altitude, fatigue, dehydration, and sleep deprivation all suppress appetite, often sharply, and the effect tends to get worse the longer the event runs and the harsher the conditions. So by the time you most need calories (day three of a multi-day race, hour 20 of a 100-miler, the third week of an expedition), your desire to eat may be at its lowest. What helps is food that stays easy to eat when appetite has gone: soft, mild-flavoured, calorie-dense and needing no preparation. For strategies on eating when appetite fails, see our guide on low appetite and difficulty eating enough calories.

Palate fatigue. Eating the same flavours and textures repeatedly across days or weeks creates food aversion. This is different from appetite suppression: you may be hungry but unable to face the food you have. Sweet foods are typically the first casualty. Gels, sweet energy bars, and sugary drinks that worked perfectly on day one become repulsive by day three. The countermeasure is variety: multiple flavours, a mix of sweet and savoury, different textures, and at least one food option that is specifically mild and neutral enough to tolerate when everything else has become unbearable. See our guide to high-calorie snacks for options.

Pack weight and volume constraints. On self-supported events and expeditions, every gram of food competes with water, equipment, shelter, and clothing. Bulky, low-calorie foods such as bread and fresh fruit fill pack space without the calories to match. Calorie density sets a hard limit on how many calories you can physically carry.

Digestive tolerance under exertion. Running, hiking, or hauling with a full stomach causes nausea, cramping, and GI distress in many people. Foods high in fibre, fat, or protein digest more slowly and can sit uncomfortably during sustained effort. The most practical approach is to eat small amounts frequently rather than large meals infrequently: a handful of food every 20 to 30 minutes instead of a full meal every three hours. Food that can be broken into pieces, eaten one-handed while moving, and consumed gradually over an hour is far more practical than food that demands a sit-down meal format. For more on foods that are gentle on the digestive system, see our guide to soft high-calorie foods.

Cumulative deficit over time. Each individual missed snack or shortened meal feels insignificant. But a 300-calorie daily shortfall (about one skipped snack a day) adds up to 1,500 calories over five days. That is enough to noticeably impair performance, mood, and recovery. The catch is that you do not feel the full effect until days after it begins, by which point the deficit is difficult to reverse mid-event.

How do you build a practical nutrition plan?

The most effective ultra-endurance nutrition plans are simple, redundant, and easy to execute when you are exhausted. Complexity is the enemy of execution at hour 30 of a race.

Think in three layers.

Layer 1: main meals. These provide routine, variety, and the largest single calorie contributions. A bowl of porridge with milk powder and nut butter in the morning. A freeze-dried or dehydrated meal in the evening. A sandwich, wrap, or substantial hot food at a checkpoint. Main meals deliver 500 to 1,000 calories per sitting and provide the psychological anchor of a "proper meal." For calorie-dense breakfast and drink ideas, see our guide to high-calorie drinks, smoothies and milkshakes.

Layer 2: snack calories. These are the foods you eat between meals: on the move, at rest stops, during transitions. In a multi-day event, snacks often account for 30 to 50% of total calorie intake. They need to be compact, accessible without stopping, and easy to eat one-handed. Bars broken into pieces, nuts, flapjacks, cheese, chocolate, dried fruit and nut butter sachets all work. Carry enough, and eat them by the clock instead of waiting for hunger. To see which bars suit race days, my comparison of energy bars for ultra running puts five side by side.

Layer 3: backup calories. This is the food you carry specifically for when layers 1 and 2 fail. When meals stop appealing, snacks make you feel sick, or you cannot face eating but know you need calories, the backup is what keeps you moving. It needs to be the most calorie-dense, easiest-to-eat, most reliable item in your pack. Something you can eat in any condition, in any state of fatigue, without preparation or decision-making: mild, soft and calorie-dense, and not something you have been eating all day.

Test everything in training. Skip anything else on this page before you skip this. Your digestive system, your taste preferences, and your tolerance for specific foods under exertion at hour 15 may be completely different from what you experience eating the same food at your kitchen table. Test your complete nutrition plan during long training sessions, ideally in conditions that approximate your target event. Discovering that your stomach rejects your chosen bar after three consecutive days is far better learned during a training weekend than on day three of a race.

Common fuelling mistakes

Most ultra-endurance nutrition problems come from planning errors rather than lack of effort during the event.

Underestimating total calorie needs. Many people simply do not carry enough usable calories. A five-day self-supported race requiring 3,000 to 5,000 calories per day means 15,000 to 25,000 total calories. Calculate your total need, calculate the weight of food required to meet it, and then check whether that weight fits your pack and your carrying capacity.

Carrying food that is too bulky for its calorie value. A plan can look good on paper but fail in practice if the food takes up too much space, weighs too much relative to its calorie content, or requires preparation that conditions do not allow.

Over-relying on sweet foods. Gels and sweet bars work well for the first 12 to 18 hours of most events. After that, palate fatigue sets in and sweet foods become increasingly difficult to tolerate. A nutrition plan that consists entirely of sweet products is a plan that will fail in the second half of any multi-day event.

Eating reactively instead of proactively. In ultra-endurance, appetite is an unreliable guide to calorie needs. By the time you feel hungry, you are already in deficit. The most effective approach is to eat on a schedule, every 20 to 30 minutes, whether or not you feel like eating. Set a timer on your watch if necessary.

Leaving fuelling decisions to race day. Decision fatigue is real in ultra-endurance. If you are standing at a checkpoint at hour 40, exhausted and nauseous, trying to decide what to eat from a pile of unfamiliar food, you will probably eat nothing. Pre-plan every meal and every snack. Remove the decision-making. Make calorie intake automatic.

Where do Phoenix Bars fit?

I make Phoenix Bars, so read this section with that in mind. They suit the conditions described in this guide: prolonged effort, limited appetite, limited carrying capacity, and places where food has to be reliable, compact and easy to eat when nothing else works.

Each one carries up to 557 calories and up to 66g of carbs in a compact, 120g bar, and they won't freeze or melt. Customers have eaten them at -45°C on a South Pole expedition, and on the Marathon des Sables one runner found they kept their shape even in desert temperatures. They can be eaten whole, broken into pieces for gradual on-the-move grazing, or mixed with water to make porridge at a checkpoint or in camp. There are six flavours (Vanilla, Cherry Bakewell, Chocolate, Salted Caramel, Ginger, and Apple & Cinnamon), and flavour variety across multi-day events helps prevent the palate fatigue that makes runners stop eating.

In the three-layer plan described above, they can work in all three layers: as a quick, calorie-dense breakfast (layer 1), as an on-the-move snack broken into pieces across an hour (layer 2), and as the reliable backup food that works when everything else has become intolerable (layer 3).

For practical guidance on different ways to use them, see how to use Phoenix Bars.

What customers have told me

Three things come up again and again in feedback from endurance athletes and expedition teams:

They work when appetite collapses. The mild, not overly sweet flavour means they remain tolerable deep into multi-day efforts when sweet gels and standard bars have become repulsive. Multiple users describe them as the last food they could still eat when everything else had stopped working.

They have held up in extreme conditions. Shaun Weston found them easy to eat at -45°C at the South Pole, Alex Welch ate one a day through the Beyond The Ultimate Ice Ultra at temperatures down to -40°C, and Paul Blinstone said they kept their shape even in desert temperatures on the Marathon des Sables.

The calorie-to-weight ratio changes how much you need to carry. At up to 557 calories in a compact, 120g bar, they let runners and expedition teams carry fewer grams of food for the same calories: on the five-day example above, about 4kg less than food at 2 calories per gram.

"I always struggle with finding enough calories when competing at long races. The Phoenix Bar has answered that question. It also tastes delicious."

"Flaming Phoenix Bars featured as a star in my food supply for my recent South Pole expedition! Easy to eat, even at -45c. Apple and cinnamon was a particular standout."

"Phoenix Bars helped me climb Mount Denali and complete a 100-mile race. The last time I climbed Denali, I lost 16 pounds. With Phoenix Bars, I only lost 8 pounds."

"Tastes mild enough to be eaten for days and days without making you sick. High in calories, which is great for ultras. Genuinely a different alternative to what's out there."

"I have one open in my pocket and just nibble away at it like a mouse as they are so calorie-dense."

For the full product range and nutritional information, see Phoenix Bars.

Frequently asked questions

What is the best food for ultra-endurance events and expeditions? Food you will actually eat when you are tired: calorie-dense (about 4.5 calories per gram or more), easy to eat on the move, needing no preparation, and in enough flavours to hold off palate fatigue. The strongest plans combine main meals, portable snacks such as nuts, cheese, flapjacks and bars, and a mild backup food kept for when everything else stops appealing.

Why does calorie density matter in multi-day events? Calorie density determines how many calories you can carry for a given pack weight. On self-supported events and expeditions where every gram matters, higher calorie density means more usable calories in less space and less weight.

How many calories do ultra-endurance athletes need per day? Typically 4,000 to 8,000 calories per day depending on activity type, intensity, terrain, conditions, and body weight. Most athletes cannot eat this much during the event, so the goal is to keep the deficit small rather than eliminate it. The British Nutrition Foundation provides general guidance on energy requirements for active individuals.

How do I avoid under-fuelling during an event? Eat proactively on a schedule rather than waiting for hunger. Carry enough calorie-dense food to meet your target. Test everything during training. Carry a reliable backup food for when your primary nutrition becomes unappealing. Use the three-layer approach described above.

What should I eat when I can't face sweet food? Palate fatigue with sweet foods is the most common reason athletes stop eating in the second half of multi-day events. Savoury checkpoint food, mild-flavoured bars, cheese, nuts, and broth-based soups all help. Carry at least one food that is not sweet, so you can keep eating when gels and sweet bars have become intolerable.

How many calories an hour can you eat during an ultra? Most people manage about 200 to 400 calories an hour while moving, which is why a 6,000-calorie day cannot be eaten on the move alone. Practising in long training runs helps your stomach handle more; our guide to gut training for ultras covers how.

How much food should you carry for a multi-day self-supported race? Multiply your daily calorie target by the number of days, then divide by the average calories per gram of your food. For 3,000 calories a day over five days, food at 4.5 calories per gram weighs about 3.3kg; at 2 calories per gram it is 7.5kg.

This guide is the first in our series on nutrition for specific endurance situations. For environment-specific and event-specific guidance, see:

• UK multi-day ultra race nutrition: fuelling in cold, wet, overnight conditions
• Marathon des Sables nutrition: desert multi-stage racing
• Polar expedition nutrition: extreme cold environments
• High-altitude mountaineering nutrition: altitude and appetite
• Cycling and bikepacking nutrition: long-distance cycling
• Ocean rowing nutrition: offshore endurance
• Military field nutrition: supplementing ration packs
• Wild camping food: food planning for UK wild camping
• Calorie-dense foods: understanding calorie density
• How to use Phoenix Bars: practical guidance including the porridge method

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

Sources: British Nutrition Foundation; typical UK pack label values for the calorie density table.