Mountaineering food and nutrition: how to eat when altitude kills your appetite

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

About this guide

Quick answer: At altitude, eat small amounts of carbohydrate-rich, ready-to-eat food by the clock, something every 1 to 2 hours, because appetite fades as you climb while the work of moving goes up. In a study of ten expedition members living at 6,542m on the summit of Sajama in Bolivia, Westerterp and colleagues (1994) measured an average shortfall of roughly 550 to 700 calories a day, and about three-quarters of the weight they lost was fat.

As you climb higher, appetite drops, digestion slows and every item in your pack gets heavier to carry. Put together, that leaves a calorie gap that lasts for days and can cost you performance, recovery and safety.

At elevations above 2,500m, most climbers and trekkers experience some degree of altitude-induced appetite loss. Above 5,000m, appetite suppression can be severe, yet a hard climbing day there can roughly double what you would burn at sea level, because moving, breathing and keeping warm all take more work in thin, cold air. Trekkers heading to Everest Base Camp meet a milder version of this, covered in our guide to Everest Base Camp nutrition.

This guide focuses specifically on practical approaches to maintaining calorie intake at altitude when appetite is suppressed, conditions are extreme, and pack weight is limited.

It covers:

• why altitude suppresses appetite and increases calorie demands simultaneously
• why the weight-to-calorie ratio of your food matters more in the mountains than anywhere else
• what food characteristics are most practical at high altitude
• how compact, calorie-dense foods can close the gap when full meals are not realistic

It also explains how mountaineers and high-altitude trekkers use Phoenix Bars, the compact high calorie bars I make (up to 557 calories in a compact, 120g bar), as part of their expedition food.

This guide is informational and should not replace medical advice about altitude acclimatisation or nutrition for specific expeditions. Consult your expedition doctor or a sports dietitian for personalised guidance.

Written by James Frost, founder of Flaming Phoenix and the maker of Phoenix Bars. Customers have carried them on expeditions to Everest and Denali, in the Sahara and in the Arctic.

Last updated: November 2026

Key points: Altitude suppresses appetite while the work of climbing pushes calorie needs up, so most climbers eat well short of what they burn above 5,000m. Every gram of food must justify its place in your pack, which makes calories per gram the number to watch. Food must not freeze in sub-zero conditions or melt in direct sun. Phoenix Bars carry up to 557 calories in a compact, 120g bar and are a source of iron, which contributes to normal oxygen transport in the body. One customer found them easy to eat at -45°C on a South Pole expedition.

Contents

1. Why altitude changes everything about eating
2. The calorie gap at high altitude
3. Common eating challenges in the mountains
4. What makes food work at altitude
5. How to keep eating when you are not hungry
6. How calorie density cuts pack weight
7. How much food to carry per day
8. How Phoenix Bars are used at altitude
9. Practical suggestions for expeditions
10. Frequently asked questions
11. Related guides

Why altitude changes everything about eating

High altitude affects eating through multiple overlapping mechanisms.

Appetite suppression. As altitude increases, the body produces hormones including leptin and cholecystokinin that suppress hunger signals. At the same time, hypoxia (reduced oxygen availability) dampens the desire to eat. Above 5,000m, many climbers report virtually no appetite, even when they know they need to eat.

Increased calorie expenditure. Moving at altitude requires significantly more effort than at sea level. The body works harder to breathe, harder to thermoregulate in cold conditions, and harder to perform any physical task with reduced oxygen. A day of climbing above 5,000m can burn 4,000–6,000+ calories depending on conditions and intensity. For a personal estimate, try our climbing calorie calculator, which also covers long alpine days.

Impaired digestion. Altitude slows gastric emptying: food sits in the stomach longer, creating a feeling of fullness and discomfort. Rich, fatty, or heavy meals can feel particularly difficult to digest. Many climbers experience nausea, bloating, and general digestive discomfort at altitude.

Dehydration. The body loses fluid faster at altitude through increased respiration and the dry air. Dehydration further suppresses appetite and impairs digestion.

Cold conditions. At high altitude, sub-zero temperatures are common, even on tropical mountains. Cold suppresses appetite independently of altitude, and the energy cost of maintaining body temperature adds to calorie demands.

Pack weight constraints. On technical mountaineering routes and high-altitude expeditions, every gram matters. Food competes with safety equipment, climbing gear, shelter, and fuel for weight and space in the pack. This creates a direct tension between carrying enough food and carrying a pack light enough to climb safely.

The combined effect is a severe mismatch: the body needs far more calories than normal, but appetite, digestion, conditions, and weight constraints all work against adequate eating. Above 5,000m, most climbers end up eating well short of their calorie needs.

The calorie gap at high altitude

The calorie deficit at altitude accumulates rapidly.

At sea level, a moderately active adult might need 2,000–2,500 calories per day. A climber above 5,000m carrying a pack and moving through technical terrain in cold conditions may need 4,000–6,000 calories per day, yet typically consumes only 2,000–3,500.

Measured studies back this up. On Sajama (6,542m) in Bolivia, Westerterp and colleagues (1994) followed ten people through a 21-day stay on the summit and reported that they were in negative energy balance throughout the study, while fat mass fell by an average of 3.7kg.

This deficit has direct consequences: weight loss and muscle wasting that accelerate with altitude and duration, fatigue that compounds daily and reduces climbing performance, impaired cognitive function that increases the risk of poor decision-making, slower acclimatisation as the body lacks the energy to adapt, and weakened immune response that increases vulnerability to illness.

On a multi-day expedition, cumulative calorie deficit is one of the most significant performance and safety risks. Climbers who maintain better calorie intake consistently perform better, acclimatise faster, and recover more effectively between climbing days. Soldiers on demanding exercises face a similar calorie gap, covered in our guide to military field nutrition.

Common eating challenges in the mountains

No appetite. Usually the hardest one to deal with. At altitude, the desire to eat can be completely absent for hours or even days. Eating becomes a deliberate, conscious act rather than a response to hunger.

Nausea. Altitude sickness, dehydration, and exertion can all cause nausea that makes eating feel impossible. Rich or heavy foods are particularly likely to trigger it.

Frozen food. At sub-zero temperatures, many foods freeze solid: bars become rock-hard, bread becomes inedible, fruit becomes an ice block. Foods that don't freeze remain edible when others fail. Staying soft in the cold is one of the main tests in our ranking of the best energy bars for expeditions.

Melting food. On sun-exposed approaches and at lower altitudes in tropical mountain environments, chocolate, many energy bars, and soft snacks melt into an unusable mess.

Limited cooking. Above certain altitudes, cooking becomes impractical: fuel is heavy, water needs to be melted from snow, and the energy to prepare a meal may not be available. Ready-to-eat foods become essential.

Taste changes. Altitude can dull taste perception. Bland foods become even less appealing. Subtle, not-too-sweet flavours tend to be tolerated better than either very bland or very sweet options.

Dry mouth and throat. The dry air at altitude, combined with mouth breathing during exertion, makes dry or crumbly foods very difficult to eat without significant water, which itself is a precious and heavy resource.

What makes food work at altitude

Food for high-altitude mountaineering and expeditions needs to be:

• Calorie-dense: maximum calories per gram of pack weight
• Won't freeze: remains soft and edible in sub-zero conditions
• Won't melt: remains intact in direct sun and warm approaches
• Lightweight and compact: every gram counts in the pack
• Ready to eat or minimal preparation: conserving fuel and energy
• Easy to eat with minimal chewing: manageable when exhausted, hypoxic, and wearing gloves
• Not sickly sweet: tolerable when appetite is suppressed and taste perception is altered
• High in carbohydrates: carbs are the most efficiently metabolised energy source at altitude, requiring less oxygen to convert to energy than fat
• Tough packaging: survives being compressed in a pack, exposed to moisture, and handled with gloves
• Contains useful vitamins and minerals: iron contributes to normal oxygen transport in the body, thiamine contributes to normal energy-yielding metabolism, and vitamin E contributes to the protection of cells from oxidative stress

How to keep eating when you are not hungry

Eat by the clock, not by appetite. Hunger signals are unreliable at altitude. Set a schedule: eat something every 2 hours, regardless of whether you feel hungry. A few hundred calories every couple of hours is easier to face than a big meal you have no appetite for.

Front-load calories at lower altitudes. Eat aggressively at base camp and during approach days when appetite is stronger. Building calorie reserves before going high provides a buffer for the days when eating becomes hardest.

Carry ready-to-eat, high-calorie snacks for climbing days. Anything that requires cooking, heating, or preparation with utensils will not get eaten on a climbing day above 5,000m. Pack food that can be eaten from a pocket with gloves on.

Choose carbohydrate-rich foods. At altitude, the body metabolises carbohydrates more efficiently than fat: carbs require less oxygen to convert to energy. High-carb, calorie-dense foods are the most practical fuel source for climbing days.

Test everything at altitude before committing. Foods that work perfectly at sea level may be intolerable at altitude due to taste changes, nausea, or texture aversion. Test your planned nutrition during acclimatisation days or training at altitude.

Porridge and liquid calories for acclimatisation days. Warm, semi-liquid foods are often the most tolerable at altitude. A calorie-dense porridge, soup, or hot drink with added calories can get meaningful calories in when solid food feels impossible. For instructions on making a porridge of up to 557 calories from a Phoenix Bar, see how to use Phoenix Bars.

Keep food accessible. Store snacks in jacket pockets, hip belt pockets, or the top of your pack, not buried at the bottom. The easier it is to reach food without stopping, the more likely you are to eat consistently.

How calorie density cuts pack weight

Calorie density (calories per gram) should decide most of what goes in your mountaineering food bag.

Every gram of food in your pack must be carried uphill, at altitude, in conditions where every additional gram of weight increases fatigue and reduces climbing performance. The food that delivers the most calories in the least weight lets you climb faster and lighter, with more left in reserve.

A typical energy gel delivers approximately 100 kcal in a 30 to 40g sachet. A standard energy bar delivers approximately 150–250 kcal at 40–60g. A Phoenix Bar delivers up to 557 kcal at 120g, about 4.6 calories per gram. Nuts and peanut butter go higher still, but they are harder to eat in quantity once appetite has gone.

For a five-day alpine push where you're carrying all your food, the weight difference between lower-density and higher-density options can be 1–2kg, weight that translates directly to speed and safety.

The table compares typical UK supermarket values for foods climbers commonly carry. Figures are approximate and vary by brand.

How much food should you carry per day at altitude?

Divide your daily calorie target by the average calories per 100g of what you pack. A mixed mountain food bag usually averages 400 to 450 calories per 100g once packaging is off, so a 4,500-calorie day needs roughly 1.0 to 1.1kg of food per person. A bag built around nuts, cheese and chocolate at about 550 calories per 100g brings that down to about 800g. The figures below are approximate and leave out packaging and stove fuel.

• 3,500 calories a day: about 1,000g at 350 calories per 100g, 800g at 450, or 650g at 550
• 4,500 calories a day: about 1,300g at 350 calories per 100g, 1,000g at 450, or 800g at 550
• 5,500 calories a day: about 1,550g at 350 calories per 100g, 1,200g at 450, or 1,000g at 550

Most climbers will not eat 5,500 calories a day high on a mountain, however much they carry. Plan the bag around what you will realistically eat at each camp, and put the densest, easiest food into the high-camp and summit-day bags where every gram matters most. For pacing your ascent, see how to acclimatise to altitude.

How Phoenix Bars are used at altitude

Phoenix Bars started as my University of Exeter idea for a high-calorie ration bar, and several things about them suit mountaineering and high-altitude expeditions.

Cold and sun, in customers' words. Shaun Weston took them on a South Pole expedition and found them easy to eat at -45°C. On a summit push, keep the next bar in an inside pocket anyway. For hot approaches, a Marathon des Sables runner said they kept their shape even in desert temperatures.

High calorie density. Up to 557 calories in a compact, lightweight 120g bar. In a jacket pocket, that is a full snack meal you can reach at any point in a climbing day.

Up to 66g of carbohydrates per bar. Carbohydrate-rich, which aligns with the body's preference for carb metabolism at altitude where oxygen is limited.

A source of key vitamins and minerals. Phoenix Bars contain naturally occurring iron (3.2mg per bar, 23% RI), vitamin E (5.2mg, 43% RI), vitamin B1 (0.4mg, 36% RI) and vitamin B7 (9.9µg, 20% RI). Iron contributes to normal oxygen transport in the body, thiamine and biotin contribute to normal energy-yielding metabolism, and vitamin E contributes to the protection of cells from oxidative stress.

Easy to eat in pieces. Break a bar up before the day starts and eat one piece at a time during rest stops, which is easier to face than a full meal when you are exhausted.

Can be made into porridge. Mixing a bar with water creates a calorie-dense porridge, ideal for base camp meals, acclimatisation days, or summit night when solid food is intolerable.

Shelf life of up to two years. Bars bought months before an expedition are still well in date for the trip (Cherry Bakewell keeps for up to 12 months).

Phoenix Bars have been carried on expeditions to Everest, Denali, Manaslu and Aconcagua.

"I took Phoenix Bars with me on Mt Teide and during my Aconcagua expedition."

"Packing a solid amount of calories and carbs into such a small product that's easy to carry and eat while out on the trails is brilliant and changed the game for me."

Practical suggestions for expeditions

Base camp and approach: Eat Phoenix Bars as calorie-dense snacks between meals to build calorie reserves while appetite is still relatively strong. Make porridge for breakfast by mixing a bar with water or milk.

Climbing days: Carry 2–3 bars in jacket or hip belt pockets. Break into pieces before the day starts. Eat one piece every 30–45 minutes regardless of hunger. Three bars provide up to 1,671 calories of easy-to-access, no-preparation climbing fuel.

Summit push: Keep a bar in an inner pocket close to your body to prevent freezing in extreme conditions. Broken into pieces beforehand, it can be eaten a bite at a time. On an 8,000m summit push, even a few bites provide meaningful calories when other food is impossible.

Rest days and acclimatisation: Use the porridge format for warm, comforting, calorie-dense meals. Add milk powder, nut butter, or honey for extra calories.

Emergency/storm days: Phoenix Bars require no cooking, no water, and no preparation. They function as a reliable emergency food that is always available regardless of conditions.

Provisioning: For a 2-week expedition, 2–3 bars per day = 28–42 bars. For a month-long expedition, 60–90 bars. The 36-bar bundle is the most practical provisioning option. Contact me directly for bulk expedition orders.

Frequently asked questions

Why does appetite drop at altitude?

Altitude triggers hormonal changes (increased leptin and cholecystokinin) that suppress hunger signals. Hypoxia, dehydration, nausea, and cold all contribute further. Above 5,000m, most climbers have very little natural appetite.

How many calories do I need at high altitude?

Depends on altitude, activity, temperature, and individual metabolism, but 4,000–6,000 calories per day is typical for active climbing above 5,000m. Most climbers fall well short of this, so a calorie deficit builds day by day.

Is carbohydrate or fat better fuel at altitude?

Both have a place. Per litre of oxygen your body uses, carbohydrate releases about 5.0 calories against about 4.7 for fat, roughly 8% more, which matters when oxygen is short. Fat carries about 9 calories per gram against 4 for carbohydrate, so it saves pack weight. Most climbers do best with carbohydrate-rich snacks on the move and some fat at camp meals.

What should I eat on summit day?

Eat a breakfast you can face before leaving camp, such as porridge, sweet tea or a few biscuits, even if it is small. Then eat a few mouthfuls every 30 to 60 minutes from an inside pocket so nothing freezes: sweets, nuts, pieces of a bar, or a gel if chewing feels like too much. A warm, sweet drink from an insulated flask often goes down when solid food will not.

Will Phoenix Bars freeze at altitude?

Not easily, according to the climbers who have used them. Matt Le Voi took 33 bars to Manaslu and Rick Wilton has carried them on Everest and Denali, and both wrote that they don't freeze easily. In the deepest cold, keep the bar you will eat next inside your jacket so it stays soft.

Are Phoenix Bars good for altitude because of the nutrients?

Phoenix Bars contain naturally occurring iron, vitamin E, B1 and B7. Iron contributes to normal oxygen transport in the body, and thiamine (B1) and biotin (B7) contribute to normal energy-yielding metabolism. Each bar also carries up to 66g of carbohydrate, and carbohydrate yields slightly more calories per litre of oxygen than fat.

Can I make Phoenix Bar porridge at altitude?

Yes. Mixing a Phoenix Bar with water creates a calorie-dense porridge. This is particularly useful at base camp and during acclimatisation when solid food is hard to face.

Related guides

• Ultra-Endurance & Expedition Nutrition Guide: broader expedition nutrition principles
• Marathon Des Sables Nutrition: extreme heat conditions nutrition
• Ocean Rowing Nutrition: similar calorie-density challenges at sea
• Calorie-Dense Foods: full explanation of calorie density
• How To Use Phoenix Bars: practical guidance including porridge method
• What to eat on Kilimanjaro: a day-by-day food plan for the climb
• Aconcagua nutrition: personal snacks and summit day food
• Denali expedition food: sled, pack and summit day food
• Manaslu nutrition guide: food for an 8,000m climb
• Ski touring nutrition
• Rock climbing food

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James Frost, founder of Flaming Phoenix and the maker of Phoenix Bars

jfrost@flaming-phoenix.co.uk | 07990 519422

Sources: Westerterp and others, Mount Sajama study, Journal of Applied Physiology (1994); Great Britain nutrition and health claims register; food table from typical UK supermarket pack values; Phoenix Bar values, including vitamins and minerals, from our own pack labels.