Military field nutrition: how to top up ration packs when you need more calories

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

About this guide

Quick answer: A British Army 24-hour ration pack holds around 4,000 calories, but a hard field exercise with a heavy bergen, cold or long tabs can burn 5,000 to 6,000 a day, and many soldiers don't eat all of what they're issued. The practical fix is to eat the whole ration and carry an extra 500 to 1,000 calories a day of compact, no-cook food you can eat on the move.

For routine field exercises and peacekeeping duties, the ration is broadly enough. For high-intensity exercises, long infantry patrols, cold-weather training, selection courses and long spells of hard physical work, it often isn't.

NATO's ration standard, STANAG 2937, recommends 3,600 calories a day for regular missions and 4,900 for combat operations and Special Forces missions. Even so, many soldiers on demanding exercises end up short, because the pace means meals are rushed, skipped or only half eaten.

This guide is about topping up issued rations with compact, calorie-dense food when they aren't enough. Rations stay the main source of food throughout. It covers:

• why calorie intake often falls short on exercise even when the ration itself is adequate
• the practical barriers to eating enough in the field
• what makes supplementary food useful in a military context
• how much extra food a five-day exercise can call for, and which foods carry the most calories for their weight

Written by James Frost, founder of Flaming Phoenix and the maker of Phoenix Bars. Nothing here is MOD guidance or issued kit: it is about the food you buy and carry yourself.

Last updated: November 2026

Key points: UK 24-hour ration packs provide around 4,000 calories, but high-intensity exercise can demand 5,000 to 6,000 or more. Soldiers often eat less than their ration provides because of time pressure, fatigue and tempo. The shortfall builds across a multi-day exercise, and with it come slower decisions and a higher risk of injury. The simplest fix is food that needs no preparation and fits in a pocket.

Contents

1. The calorie gap on exercise
2. Why soldiers don't eat enough in the field
3. Why the calorie deficit matters operationally
4. What makes supplementary food useful in the field
5. How to keep eating on exercise
6. How calorie density saves bergen weight
7. The best foods to top up army rations
8. How Phoenix Bars fit into field nutrition
9. Practical suggestions for exercise and operations
10. Frequently asked questions
11. Related guides

The calorie gap on exercise

The UK 24-hour Operational Ration Pack (ORP) provides around 4,000 calories across its main meals, snacks and drinks. For standard duties and moderate-intensity field exercises, this is broadly adequate.

However, the calories burned on demanding exercises often exceed what a ration pack provides.

Infantry soldiers on sustained patrol can burn 4,000–6,000+ calories per day depending on load carried, terrain, pace, and environmental conditions. Cold weather operations increase calorie expenditure significantly: the body burns additional energy simply to maintain core temperature. High-altitude operations, selection courses, and prolonged tabbing with heavy loads push expenditure even higher.

NATO's ration standard allows for this: STANAG 2937 recommends 4,900 calories a day for combat operations and Special Forces missions, against 3,600 for regular missions.

In practice, the gap widens further because many soldiers don't eat all of their issued rations: items get stripped out to save weight, meals get skipped when the tempo is high, and food fatigue sets in by day three or four.

So the deficit builds day on day. By day 3, 4, or 5 of a demanding exercise, the accumulated shortfall can amount to thousands of missing calories.

How big does the calorie gap get over five days?

The table assumes a 4,000-calorie ration. The burn figures are rough estimates; yours depends on body weight, load, distance and temperature.

A top-up of 1,000 calories a day, about 220g of food at 4.5 calories per gram, closes the second case completely and halves the third. Eating the whole ration matters as much as the extra food.

Why soldiers don't eat enough in the field

Even when rations are adequate on paper, several factors consistently reduce actual calorie intake in the field.

Operational tempo. When the pace of operations is high, meals get compressed, interrupted, or skipped entirely. There is often no protected time for eating: food competes with tasks, movement, and rest.

Time to prepare. Boil-in-the-bag main meals require water, a heater or stove, and time. In tactical situations or during rapid movement, the 10–15 minutes needed to prepare a hot meal may not be available. Cold food straight from the pouch is an option but is significantly less appealing and often only partially eaten.

Weight management. Soldiers carrying heavy loads often strip non-essential items from their ration packs to save weight. Snack items, drinks, and sundries are frequently the first things removed, yet these account for a significant proportion of total ration calories.

Fatigue and appetite suppression. Physical exhaustion suppresses appetite. After hours of tabbing under load, the desire to eat can be minimal even when the body desperately needs fuel. Sleep deprivation compounds this: hunger signals become unreliable.

Stomach discomfort. Eating large meals during sustained physical activity can cause nausea, cramping, and GI distress. Many soldiers avoid eating significant amounts before or during movement for this reason.

Environmental conditions. In extreme cold, handling food with gloved hands and eating in exposed positions is difficult. In extreme heat, some ration components deteriorate and appetite drops.

Monotony. The limited menu rotation of ration packs across multi-day exercises creates food fatigue. By day 3 or 4, few soldiers want to eat the same meals again.

Why the calorie deficit matters operationally

A calorie deficit in the field quickly becomes an operational problem.

Cognitive function degrades. Decision-making, reaction time, situational awareness, and judgement are all impaired by calorie deficit. Several days of underfeeding, usually alongside lost sleep, shows up as slower decisions and lapses in attention.

Physical performance drops. Endurance, strength, and load-carrying capacity all decline as calorie deficit accumulates. Soldiers performing at a calorie deficit are slower, weaker, and fatigue faster.

Injury risk increases. Fatigue and reduced concentration from underfeeding increase the risk of training injuries, accidents, and poor decision-making in high-risk environments.

Recovery slows. After demanding exercise phases, calorie-depleted soldiers take longer to recover physically and mentally. This affects readiness for subsequent phases of an exercise or operation.

Morale suffers. Hunger, fatigue, and the psychological effect of running on empty compound the mental demands of field conditions. Adequate fuelling is a morale factor as well as a performance one.

What makes supplementary food useful in the field

The most useful supplementary food for military field use shares specific characteristics, most of which also define the best energy bars for expeditions.

Compact and lightweight. Every gram competes with ammunition, water, equipment, and other essentials. Supplementary food must deliver meaningful calories without adding significant weight or bulk. It needs to fit in a pocket, pouch, or the top of a bergen without taking up space needed for other kit.

High calorie density. The ratio of calories to grams carried is the defining metric. A supplement that delivers up to 557 calories at 120g packs about 50% more calories per gram than one delivering 150 calories at 50g (about 4.6 against 3 per gram).

No preparation required. Open and eat. No water, no stove, no time. Anything that requires preparation will not get eaten when the operational tempo is high.

Climate stable. Must not melt in desert heat or freeze solid in arctic conditions. A bar that freezes solid or melts in its wrapper is just extra weight.

Tough packaging. Must survive being compressed in a bergen, exposed to rain, handled with dirty or gloved hands, and carried for days. Packaging that tears, splits, or disintegrates under field conditions is useless.

Quiet to open and eat. In tactical situations, noise discipline matters. Food that requires noisy packaging or extended chewing may not be appropriate for all phases of an exercise.

Not sickly sweet. Sweetness fatigue is a real issue over multi-day exercises. Supplements that are excessively sweet become difficult to tolerate after the first day or two. A neutral, savoury, or mild flavour profile sustains better over time.

Soft texture. When fatigued, dehydrated, or cold, chewing hard or dry food is difficult and slow. Soft food that melts in the mouth can be eaten quickly and with minimal effort.

How to keep eating on exercise

Several approaches can help close the calorie gap in the field.

Carry personal supplements alongside issued rations. Don't rely on rations alone for multi-day exercises. Add 500–1,000 extra calories per day in the form of compact high calorie bars or other calorie-dense food that fits in a pocket or the top lid of your bergen.

Eat on the move. Rather than waiting for meal breaks that may be shortened or cancelled, eat small amounts during movement. Food that can be eaten one-handed, in small bites, without stopping, keeps calorie intake ticking over throughout the day.

Don't strip food from your rations to save weight. The snacks and sundries in a ration pack are not luxuries: they are a significant proportion of the daily calorie total. If weight is a concern, carry a compact calorie-dense supplement instead of removing ration components.

Eat before you're hungry. Hunger signals are suppressed by exertion, sleep deprivation, and cold. By the time you feel hungry in the field, you are already in calorie deficit. Eat by the clock or by opportunity, not by appetite.

Front-load calories at the start of the day. A calorie-dense breakfast before the day's activity begins sets a foundation. If the rest of the day is disrupted, at least the morning calories are banked.

Use the evening meal window. When the pace slows (whether at a harbour area, bivouac, or end of a phase), take advantage of the opportunity to eat a full meal plus additional supplementary calories.

How calorie density saves bergen weight

Calorie density (calories per gram of weight carried) is the most important metric for field nutrition.

A soldier on a demanding exercise is already carrying 25–40kg of equipment. Every gram of food added to that load must justify itself in calorie value. Carrying 500g of food that delivers 1,000 calories is far more efficient than 500g that delivers 500.

For context: a standard issue biscuit from a ration pack delivers approximately 80–100 calories at 25g. A handful of trail mix delivers approximately 150 calories at 30g. A Phoenix Bar delivers up to 557 calories at 120g, up to about 464 kcal per 100g.

Two Phoenix Bars weigh 240g and deliver up to 1,114 calories. Getting the same calories from ration biscuits at the figures above would take roughly 280 to 350g.

When pack weight is already at its limit and the calorie gap is real, the most calorie-dense option available is the one that closes the gap without breaking the bergen.

What are the best foods to top up army rations?

The best top-up foods are dense, need no cooking and are ones you will actually eat when tired. Nuts and peanut butter carry about 600 calories per 100g, so 1,000 extra calories weighs under 200g, while a wet main meal needs about 870g for the same. Figures are typical UK values and vary by brand.

Fat-heavy foods like nuts carry the most calories for their weight, but on a long tab carbohydrate is what keeps you moving, so pair them with something like flapjack or wraps. Pick two or three you have already eaten in training, because day four of an exercise is a poor time to find out a food doesn't agree with you.

How Phoenix Bars fit into field nutrition

I make Phoenix Bars, so read this section with that in mind. They carry up to 557 calories in a compact, 120g bar, with up to 66g of carbs and up to 19g of protein. The features that matter in the field are below.

Have held up in heat and cold, by customers' accounts. A Marathon des Sables runner said they didn't melt in the heat, and Shaun Weston found them easy to eat at -45°C on a South Pole expedition.

Require zero preparation. Unwrap and eat. No water, no stove, no time, no utensils. Can be eaten one-handed while moving.

Are quick to eat. Broken into pieces, a bar goes down in a short halt, even when you are tired.

Are not sickly sweet. Six flavours (Vanilla, Cherry Bakewell, Chocolate, Salted Caramel, Ginger, Apple & Cinnamon) help with the sweetness fatigue that sets in with very sweet snacks after a day or two.

Can be made into porridge. Mix a bar with water and it becomes a calorie-dense porridge, a quick meal with no stove needed. For instructions, see how people use Phoenix Bars.

Have a shelf life of up to two years (Cherry Bakewell up to 12 months). Can be bought in advance, stored in a locker or kit bag, and used whenever needed, with no expiry concerns for exercise planning.

"I bought Phoenix Bars as I was looking for high-calorie, lightweight nutrition for military exercises and they were really good. The taste much better than I expected for something that's so nutritious."

Practical suggestions for exercise and operations

Before the exercise

Pack 1 to 2 Phoenix Bars per day into the top lid of your bergen or in smock/trouser pockets. Over a 5-day exercise, that's 5 to 10 bars: roughly 2,650 to 5,570 extra calories depending on flavour, for 600g to 1.2kg of extra weight.

In the morning

Before first light or before moving off, eat a bar or make a quick porridge with water. This front-loads up to 557 calories before the day's activity begins, a significant buffer against missed or shortened meals later in the day.

On the move

Break half a bar into pieces before stepping off. Eat a piece every 30–60 minutes during movement. This adds roughly 265 to 280 calories across a march phase, without stopping to eat.

In harbour areas and admin periods

Eat a full bar alongside your issued ration. Up to 557 extra calories and up to 19g of protein on top of the main meal help close the cumulative deficit.

At night

Keep a bar in your sleeping system. If you wake during the night or before first light, eat half a bar to prevent the overnight calorie gap that leaves soldiers starting the next day already depleted.

In cold weather

Keep the next bar in a chest pocket in hard frost, so you can reach it with gloves on and without opening your bergen.

On selection and assessment courses

On long, high-output courses where eating opportunities are short, a bar in a pocket can be eaten in a brief rest window. Check the joining instructions first, as courses differ on what personal food you can carry.

Frequently asked questions

How many calories do soldiers need on exercise?

NATO's ration standard, STANAG 2937, recommends 3,600 calories a day for regular missions and 4,900 for combat operations or Special Forces missions. Hard exercises with heavy loads, cold or long moves can push needs above 5,000 calories a day.

What should I eat during military selection?

Eat all of the food you are given, eat little and often rather than waiting for hunger, and stick to food your stomach already knows from training. Practise eating on the move during your training tabs, and check the course joining instructions before you pack anything extra, because rules on personal food vary.

Are UK ration packs enough?

The UK 24-hour ration pack provides around 4,000 calories, which is broadly enough for moderate exercise. On demanding multi-day exercises, selection courses and sustained high-output operations, many soldiers come up short, particularly when the tempo leaves little time to eat.

Will Phoenix Bars melt in hot conditions?

Customers who have used them in the heat say not. Matt Hill took them on the Marathon des Sables and wrote that they didn't melt in the heat, and Paul Blinstone said they kept their shape even in desert temperatures.

Will Phoenix Bars freeze in cold conditions?

Not easily, according to customers. Liam Steinbeck ate five on the Spine Race and Rick Wilton has used them on Denali, and both say they don't freeze easily. In hard frost, carry the next bar in a chest pocket.

How many Phoenix Bars should I take on exercise?

1–2 bars per day provides between 529 and 1,114 supplementary calories, depending on flavour. Over a 5-day exercise, 5–10 bars (600–1,200g) adds meaningful calorie insurance without significant weight penalty.

Can Phoenix Bars replace ration packs?

No. They are a top-up eaten alongside issued rations, to fill the gap between what rations provide and what demanding exercises require.

Are Phoenix Bars suitable for vegan or gluten-free soldiers?

Yes. Phoenix Bars are vegan and made with gluten-free oats, which helps if a standard ration menu doesn't suit your diet.

Related guides

You may also find these guides helpful:

• Ultra-endurance and expedition nutrition guide: broader guide to nutrition for extreme endurance situations
• Calorie-dense foods: what they are and when they help: a full explanation of calorie density
• How to use Phoenix Bars: practical guidance including the porridge method
• High-altitude and mountaineering nutrition: if operating at altitude

Buy Phoenix Bars

James Frost

Founder, Flaming Phoenix

jfrost@flaming-phoenix.co.uk

07990 519422

Sources: NATO ration standard STANAG 2937; Forces News, We try a British Army ration pack (May 2025); McCance and Widdowson's CoFID 2021.