Rucking nutrition: how to fuel long rucks and selection prep

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

Quick answer: On rucks longer than two hours, eat 200 to 300 calories an hour (300 to 400 with a heavy pack or in the cold), starting in the first hour and in small amounts every 30 to 45 minutes. Under 90 minutes, a normal meal two hours before and water are enough.

A loaded ruck burns more than a walk, and at military pace with a heavy pack on grass or hills it can reach two to three times the cost of an easy unloaded stroll. For short fitness rucks, you can ignore that. Once a ruck passes the two-hour mark, the calorie cost stops being something you can coast through. The longer the ruck, the heavier the pack, the worse the weather, and the more serious the training goal, the closer rucking nutrition gets to endurance or expedition nutrition.

This guide covers how to fuel short conditioning sessions, multi-hour training rucks, selection prep tabbing and all-day loaded carries. It addresses what most generic rucking food advice gets wrong: the calorie maths, the sweets fatigue problem, and why, past two hours, dense high calorie bars and nuts do more for you than a pre-ruck banana.

In this guide

• Why rucking nutrition is different from walking and running
• The calorie maths of rucking at common pack weights
• The 2-hour line: when rucking nutrition changes entirely
• What most rucking nutrition advice gets wrong
• Why calorie density beats sugar content on long rucks
• Practical fuelling by ruck duration
• Selection prep and multi-day rucking nutrition
• How Phoenix Bars fit into a rucking fuel plan
• Common rucking nutrition mistakes

About this guide

Written by James Frost, founder of Flaming Phoenix and the maker of Phoenix Bars. Customers have used them on military exercises, across the Sahara and on expeditions to the South Pole.

For broader guidance on loaded endurance nutrition, see the ultra-endurance and expedition nutrition guide. For practical guidance on using Phoenix Bars in the field, see how to use Phoenix Bars.

Last updated: November 2026.

Why rucking nutrition is different

Rucking looks like walking. Nutritionally it behaves more like hiking under load or a slow trail run. The added weight, typically 7 to 20kg (15 to 45 lb) for fitness rucking and 20 to 36kg (45 to 80 lb) for military training, adds to the cost of every kilometre, and pace, hills and soft ground multiply it. An 80kg person walking at 6.4 km/h (4 mph) with no pack burns about 490 calories an hour. With a 15kg (33 lb) pack on flat tarmac that rises to about 570, with 25kg (55 lb) on grass to about 730, and with 20kg (44 lb) on a hilly trail to about 1,050.

That calorie burn is substantial, but it's not the only thing that makes rucking nutritionally distinct. Three factors separate rucking from other endurance activities:

Load compresses your stomach. A loaded pack changes your biomechanics and puts mechanical pressure on your gut. Many ruckers find that eating more than small amounts while moving causes nausea, cramping, or reflux. Drinking more will not fix it; the cause is the load pressing on your gut.

Blood is shunted to working muscles. Under load, digestion slows. Food sits heavier. Large meals before or during a ruck often don't get absorbed well and sit like a brick in your pack belt.

Pace is steady, so hunger signals stay quiet. Rucking doesn't feel intense enough to trigger the urgent fuelling instincts you'd get during a run. Many ruckers drift into significant calorie deficit without realising until the last mile, when their pace collapses and their mood tanks.

Under 60 minutes, you can ignore all three. Past two hours, they decide how the last mile goes.

How many calories does rucking burn?

The most widely used model is the Pandolf load-carriage equation, developed at the US Army Research Institute of Environmental Medicine. Field studies have found it under-predicts real-world cost, so the figures below use the same equation as our rucking calorie calculator, including its 15% field correction. They are for an 80kg person at 6.4 km/h (4 mph), the usual military pace, rounded to the nearest 10, so treat them as approximate.

Slow to a steady 5 km/h and the flat-tarmac figure with a 15kg pack drops to about 400 calories an hour. Pace, gradient and surface move the number more than the last few kilos in the pack.

Plug those numbers into a 4-hour ruck with a 20kg (44 lb) pack at 5 to 6 km/h on rolling UK trails, and you're looking at about 2,400 to 3,100 calories burned. An all-day 8-hour tab under the same load can exceed 5,000 calories. A multi-day selection-prep weekend doing back-to-back long rucks can total 10,000 to 15,000 calories across 48 hours.

Most people can only comfortably eat 200 to 400 calories an hour while moving under load, which is below the burn rate of almost any ruck. A calorie deficit during rucking is therefore structural, not optional. The question is how large that deficit gets, and whether it becomes large enough to compromise the ruck, the recovery, or both.

The 2-hour line

Rucking nutrition advice falls into two halves divided by the 2-hour mark.

Under two hours, hydrate properly, eat a normal meal 2 to 3 hours beforehand, maybe a banana or a gel midway if you're going hard. That's about all that matters. Your glycogen stores carry you through.

Over two hours, glycogen starts to run down. The calorie deficit starts to build. Blood sugar drops if you haven't been eating proactively. Pace slows, mental focus degrades, motivation drops. This is where fuelling strategy becomes performance strategy.

Most online rucking nutrition content treats rucking as a 60 to 90 minute activity. That's fine for fitness rucking. It's inadequate for selection prep, military-grade training, competitive rucking events, or anyone rucking to build endurance. If your rucks are getting longer, your fuelling needs to change, not scale.

What most rucking nutrition advice gets wrong

Having reviewed the dominant rucking nutrition content online, four patterns stand out.

Over-reliance on sweet carbs. Gummy bears, sports gels, gummy sweets, Swedish fish, Honey Stinger waffles. These work for 60 to 120 minutes. Past that, palate fatigue sets in and sweet foods become actively unpalatable. A nutrition plan built entirely on sugar will fail you on a 4-hour plus ruck.

Generic "pack a protein bar" advice. Most commercial protein bars are 180 to 250 calories in 50 to 60 grams. They're fine for a quick snack but deliver poor calorie density for what you're actually burning. A 220 kcal bar every 90 minutes across a 6-hour ruck provides roughly 900 calories while you've burned 3,500+. Denser food closes that gap faster, and our guide to the best energy bars for hiking compares the options.

Treating rucking like running. Runners absorb carbs at 60 to 90 g per hour via gels and liquid. Many ruckers under load struggle to stomach that much, and most don't want liquid carbs anyway. The running blueprint doesn't transfer cleanly.

Ignoring cold and wet conditions. In the UK you're rucking in 4 to 12 degrees Celsius, in rain, for most of the year. Cold increases calorie burn, suppresses appetite, and makes handling food with gloved hands a real problem. Most US-origin rucking content skips this entirely.

Calorie density: the number that matters on long rucks

For rucks over 2 hours, the question that matters is how many usable calories you can carry for the weight. You're already carrying a heavy pack. Every additional gram of food competes with water, kit, and layers.

Calorie density varies more across common rucking food than most people expect. These are typical values, rounded, so check the labels on what you pack.

Here is what that means in your pack. Carrying 3,000 calories as gels alone means 1,000 to 2,000g of gel. Dense high-calorie bars bring that down to about 650 to 680g, and nuts to about 460 to 550g. On a loaded ruck, every 500g saved is half a litre of water, a dry mid-layer or a pair of dry socks. For the same sums on other trail foods, see our guide to the lightest high calorie food for backpacking.

That is why a long-ruck food bag tends to end up as a mix of dense bars, nuts and a few sweets rather than the sugar-led plan most rucking content recommends.

How much should you eat on a ruck?

For short rucks under 90 minutes, eat a normal meal two hours beforehand and drink water during. You do not need to eat on the move.

For rucks of 90 minutes to 2 hours, eat 200 to 300 calories about 60 minutes in, such as half a dense bar, a banana or a gel, with water or an electrolyte mix.

On long rucks of 2 to 4 hours, aim for 200 to 300 calories an hour starting in the first hour. Mix your carbohydrate sources, one sweet and one not, carry 30 to 50 percent more food than you expect to eat, and drink electrolytes.

On all-day rucks of 4 to 8 hours, aim for 250 to 400 calories an hour and eat on a schedule, typically every 30 to 45 minutes. Do not rely on sweet food past hour three. Keep at least one high-calorie, low-volume item for the hour 4 to 6 window, when appetite usually drops: a dense bar, a nut butter sachet or a flapjack.

On multi-day rucks and selection prep, treat nutrition as a 24-hour problem rather than a ruck-window one. Front-load calories at breakfast, eat a substantial recovery meal within 90 minutes of finishing, and go to bed properly fed. The deficit that builds from day to day does more damage than hunger within a single day. For longer unweighted distance work, see our guide to long-distance walking nutrition.

Selection prep: rucking nutrition at volume

If you're training for UK military selection (P Company, AACC, PRMC, UKSF Selection) or equivalent US programmes, weekly rucking volume can climb above 50 miles (80km). That volume, done at pace and under load, puts you in expedition-level calorie territory without an expedition's logistical support. For a full treatment of selection-period fuelling strategy, see our guide to nutrition for UK military selection.

Three things to get right:

Recovery between sessions. The rucker who finishes Friday's 10-miler still in calorie deficit will start Saturday's 20-miler underfuelled. Across a 12-week build, that compounds into injury risk and stagnating performance.

Sustainability of your fuelling plan. If your long-ruck plan relies on food you are sick of by week four, you'll abandon it. The food you carry has to be palatable across dozens of uses and stable through the conditions you train in.

Testing everything. The food that works at hour two of a training ruck may not work at hour six of a selection assessment in February rain. Test your fuel under realistic conditions, not on a flat 5k around a park.

Where Phoenix Bars fit in a rucking plan

I make Phoenix Bars, so here is where they fit on a long ruck.

Up to 557 calories in a compact, 120g bar. High calorie density means fewer grams of food in your pack for the same calories, which matters on long rucks when you are already near your pack weight limit. Nuts are denser still, so a mix of the two works well.

Easy to eat in pieces. You can break a bar into pieces and eat it in small amounts across an hour rather than in one sitting, which suits a stomach under a loaded hip belt.

Stable in temperature extremes. They don't melt in summer heat or freeze solid in a cold UK winter. Phoenix Bars have been used on South Pole expeditions at -45°C and across the Sahara during the Marathon des Sables.

Six flavours, none sickly sweet. Vanilla, Cherry Bakewell, Chocolate, Salted Caramel, Ginger, and Apple & Cinnamon, which makes them easier to keep eating across long training blocks than very sweet sports products.

Can be turned into porridge. Mixing a bar with water turns it into a calorie-dense porridge. See how to use Phoenix Bars for the full method. Useful for recovery between training sessions in cold weather, or as a morning pre-ruck meal option that takes 60 seconds to prepare.

Phoenix Bars come into their own on the long sessions, the selection prep weekends, and the recovery periods between back-to-back tabbing days.

"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."

Common rucking nutrition mistakes

Not eating early enough. The most common mistake. Ruckers wait until they feel hungry or low, by which point they're already behind. Start fuelling at hour one.

Eating too much in one sitting. Under load, large amounts of food sit badly. Break it up. Small amounts every 30 to 45 minutes beats one large snack halfway through.

Sweet-only plans. Sugar is fine for the first two hours. Past that, you need variety. Plan to have at least one non-sweet food option in your pack for long rucks.

Ignoring cold-weather calorie burn. Rucking in the cold increases calorie expenditure by 10 to 30 percent depending on conditions. Most ruckers under-fuel in winter specifically because appetite is lower.

Skimping on pre-ruck dinner. Muscle glycogen is largely topped up by what you eat the day before, so a proper carb-rich dinner matters as much as breakfast for a morning ruck.

Testing new food on an important day. Standard endurance rule. If you haven't eaten it on 10+ previous training rucks, don't bring it on a selection weekend or rucking event.

Frequently asked questions

How many calories should I eat per hour while rucking? On rucks over 2 hours, aim for 200 to 300 calories per hour at lower pack weights, and 300 to 400 at heavier weights or in cold weather. Most ruckers struggle to eat more than about 400 an hour under load.

How much food should I carry for a long ruck? Multiply the hours by 200 to 300 calories (300 to 400 with a heavy pack or in the cold) and add 30 to 50 percent spare. For a 4-hour ruck that is roughly 1,000 to 1,800 calories, or about 230 to 400g of dense food such as nuts, flapjack and high-calorie bars.

What should I eat before a long ruck? A carb-rich meal 2 to 3 hours beforehand. Porridge with honey and banana is the UK classic. Avoid high-fibre, high-fat, or unfamiliar foods pre-ruck.

Are protein bars good for rucking? Standard protein bars are fine for short rucks but typically under-deliver on calories for rucks over 3 hours. For those, add denser food such as nuts, flapjack or a high-calorie bar, with dried fruit for variety.

How do I fuel during UK winter rucking? Expect 10 to 30 percent higher calorie burn than summer. Pre-unwrap food or use bars with easy-open packaging to handle with gloves. Food that stays soft in the cold beats anything that goes rock hard, so check how your snacks behave after a night in the fridge before you rely on them in February.

Can I use Phoenix Bars for rucking? Yes. They're particularly suited to rucks over 3 hours, selection prep sessions, and multi-day training weekends where calorie density matters.

What do military selection candidates eat during rucking? On issued training, soldiers use Operational Ration Pack components. On self-directed rucking prep, candidates typically carry a mix of dense high-calorie bars, energy bars, nut butter sachets, flapjacks, dried fruit and jerky. See our guide to nutrition for UK military selection for detailed guidance.

Related guides

• Ultra-endurance and expedition nutrition guide: the broader framework for loaded endurance
• Nutrition for UK military selection: fuelling the specific demands of selection prep
• Hiking and trekking nutrition: unweighted multi-day walking
• Long-distance walking nutrition: distance-focused rather than load-focused efforts
• Calorie-dense foods: the numbers behind calorie density
• How to use Phoenix Bars: practical guidance including the porridge method
• Tactical athlete nutrition
• Hybrid athlete nutrition

Sources: Pandolf, Givoni and Goldman, the Pandolf load-carriage equation, Journal of Applied Physiology (1977); food values from typical UK pack labels, rounded; Phoenix Bar values from our own pack labels.