Fastpacking nutrition: how to fuel multi-day runs when every gram counts

Written by James Frost, founder of Flaming Phoenix. Updated October 2026.

Quick answer: A 70kg fastpacker moving for 8 hours burns about 5,000 calories a day, but on a trip of a few days it is normal to carry 3,000 to 4,500 a day and accept a deficit. Choose food that averages at least 4.4 calories per gram and a day's food weighs 700g to 1kg.

Fastpacking sits between trail running and lightweight backpacking: you carry your shelter, sleeping kit and all your food, but you cover ground at something closer to a run than a walk. This page works through the numbers for a UK fastpack: what you burn, which foods carry the most calories per gram, a weighed three-day food bag, and where you can buy food on the main long-distance routes. The principles shared by every multi-day event are in the ultra-endurance and expedition nutrition guide.

How is fastpacking food different from backpacking food?

You eat like a backpacker but carry like a runner. A backpacker can stop for a cooked lunch and live with a heavy pack; on a fastpack every extra 100g goes up every climb, and most of the eating happens on the move, out of a vest or hip-belt pocket.

It is a different problem from a trail run, where you fuel for a few hours and go home to a kitchen, from bikepacking, where frame bags take the weight off your back, and from long-distance walking, where there is time to stop and cook. For day hikes and slower weekend trips, hiking and trekking nutrition is the better guide. A fastpack puts an ultra's calorie bill into every day while capping how much food you can carry, so two numbers decide the food bag: calories per day and calories per gram.

How many calories do you burn fastpacking?

A full fastpacking day burns roughly 3,500 to 6,500 calories, depending on body weight and hours on the move. The NHS uses 2,000 calories for an average woman and 2,500 for an average man (NHS: understanding calories), so a fastpack roughly doubles a normal day.

Here is the working. The 2024 Adult Compendium of Physical Activities rates backpacking at 7.0 METs, and one MET burns roughly 1 calorie for every kilogram you weigh, every hour. A 70kg person moving for 8 hours burns 7.0 x 70 x 8 = 3,920 calories, plus about 1,120 for the other 16 hours at around 1 MET: about 5,040 in all. Running sections push the moving figure up, and long flat walking pulls it down.

The table shows a day's burn on the same basis: 7.0 METs while moving and 1.0 for the rest of the 24 hours.

Hardly anyone carries that much. Andrew Skurka, the American long-distance hiker, recommends packing about 3,000 calories a day for trips under two weeks, and packed 4,750 to 5,000 a day for a long expedition (his food planning notes). On a two or three day fastpack, a gap of 1,000 to 1,500 calories a day is something most people can carry and eat back afterwards. On a week or more, carry more or plan resupply.

Which foods carry the most calories per gram?

Oil, nuts and nut butter carry the most, at 6 to 9 calories per gram; chocolate, crisps, salami and dense bars sit between 4.2 and 5.2; dried fruit and wraps come in under 3. Skurka's own rule is at least 125 calories per ounce, which is about 4.4 per gram, and that is the average I would aim for across a day's food.

The figures below are per 100g from the UK's McCance and Widdowson (CoFID) tables, except Phoenix Bars (our label) and the freeze-dried meal (Expedition Foods' Chicken Tikka with Rice, 800 calories in 132g dry, which needs 265ml of water). The last column is how much of each food it takes to carry 1,000 calories.

Put the two ends side by side: 1,000 calories of apples weighs almost 2kg, and the same calories in salted peanuts weigh 166g. The densest foods are not always the easiest to live on, though. Oil only works stirred into a meal, and a bag of macadamias is hard going with a dry mouth, so a working food bag mixes very dense food with food that is easy to eat on the move. For longer rankings, see high-calorie snacks ranked by calories per gram, my list of calorie-dense foods and the lightest high-calorie food for backpacking.

What should you eat on the move, and what at camp?

Eat little and often while moving, and save the fattiest, heaviest food for camp. The International Society of Sports Nutrition's 2019 position stand on ultramarathon nutrition suggests 150 to 400 calories an hour during long efforts and advises against intakes that stay below 200 an hour, which is a fair guide for a fastpack too.

Food for the move has to live in a front pocket, open with one hand and go down in a few bites: pieces of bar, nuts, chocolate, a flapjack. Wraps, cheese and salami are easier at a stop. Felix Milne, who uses Phoenix Bars on multi-day fell and trail running events, put it this way: "The bars are light, compact, calorie dense and make staying on top of one’s nutrition very simple." My list of the best foods for ultra running has more food that works on the move, and the round-up of the best energy bars for ultra running compares bars by calories.

Camp is where the dense, fatty calories go in: a freeze-dried meal with a spoon of olive oil stirred through, wraps with cheese, the chocolate you have been saving. Breakfast works the same way, and the high-calorie breakfast guide has ways to add calories to a bowl of porridge.

Do you need a stove for fastpacking?

No. On most UK overnighters and two or three day trips you can eat well without one; on longer or colder trips, a small stove is usually worth carrying for a hot dinner and hot drinks.

Weigh your own stove, gas and pot together and turn the figure into food. If they come to 350g, that is the weight of about 1,550 to 1,600 calories of Phoenix Bars (350 x 4.4 to 4.6). On a two-day trip in June that is a lot of food to give up for hot water; on a week in the Highlands in October, hot food may be worth more to you than the calories.

Without a stove, dinner becomes cold-soaked oats, couscous or noodles, wraps with cheese and nut butter, and bars. The no-cook backpacking meals guide covers cold soaking properly. A Phoenix Bar stirred into water makes a thick porridge, and how to use Phoenix Bars gives the method. If you do take a stove, the best freeze-dried meals for backpacking compares meals by calories and weight.

A worked 3-day fastpack food plan

Here is a weighed food bag for a three-day, two-night fastpack for a 70kg runner: breakfast at home on day one, two camp dinners, and a finish by mid-afternoon on day three. Calories and weights come from the CoFID values above, the freeze-dried meal's own label and our label for each Phoenix Bar flavour.

Day two, the full day

The table lists everything carried for the middle day, the only one with all four meals coming out of the pack.

That is about 1,200 calories short of the 5,040 a 70kg person burns in 8 hours on the move, which is the deficit this plan accepts.

The three days together

Days one and three carry less because one meal on each is eaten off the trail. Day three also leans on bars, porridge and chocolate, which are easier than wraps and salami when appetite starts to fade. The table totals the whole bag on the same basis.

That is five Phoenix Bars, one each of Chocolate, Vanilla, Ginger, Apple & Cinnamon and Cherry Bakewell. Add the sixth flavour, Salted Caramel (529 calories), as a spare in case you are slower than planned, and the bag comes to 2,009g and 9,245 calories.

How do you plan food on UK fastpacking routes?

Find the longest gap between shops and carry food for that, plus one spare meal. UK routes are short next to American thru-hikes, but the gaps vary a lot. Lengths and start points below are from National Trails and Walkhighlands.

The last three have their own food guides: West Highland Way food, Pennine Way food and Cape Wrath Trail food, which lists the resupply stops. For one-day rounds, see the Bob Graham Round nutrition guide and the Welsh 3000s. Small village shops and petrol stations usually have flapjacks, peanuts and chocolate, but you cannot count on much more, so bring your densest food from home and treat resupply as a top-up.

What if you can't face food by day three?

Plan for it before you start: by the third day, tiredness and broken sleep blunt many people's appetite just as the calorie gap is at its largest. Three things help.

• Different tastes: rotate sweet, salty and savoury, and pack one food you will still want when nothing else appeals.
• Soft food: when chewing feels like work, porridge, chocolate and soft bars go down where jerky and wraps do not.
• Density: if you can only manage 300g of food on the last day, 300g at 4.5 calories per gram is 1,350 calories; at 3 calories per gram it is 900.

If you cannot eat anything for several hours, treat it as a reason to shorten the day. Our guide to multi-day ultra running nutrition covers the same late-race appetite problem over longer events.

Where do Phoenix Bars fit on a fastpack?

As one dense, easy part of the food bag. Phoenix Bars carry up to 557 calories in only 120g (4.4 to 4.6 calories per gram), with up to 66g of carbohydrate and up to 19g of protein. They break into pieces for eating on the move and stir into water as porridge at camp, and six flavours help when one taste starts to pall. They keep for up to two years (Cherry Bakewell 12 months), so a spare can live in the pack between trips.

Marc Ryder took them on a fastpack in Wales: "Recently used them on a 42 mile fast pack across the Brecon Beacons and they delivered what I needed." At £5.25 a bar, the six-bar Short-Term Bundle (£31.50, one of each flavour) is the three-day plan above with its spare, and the 12-bar Starter Bundle (£63) covers a longer trip or a trip plus training runs. If you are comparing high calorie bars, the per-gram figure in the table above is the one to check.

Fastpacking food: common questions

How heavy should a day of fastpacking food be? Aim for 700g to 1kg a day. At 4.4 to 4.7 calories per gram, that carries roughly 3,100 to 4,700 calories, which covers what most people take on trips of a few days. If your bag is heavier than 1kg a day, swap low-density food (fresh fruit, wraps, dried fruit) for nuts, chocolate or dense bars.

Is fastpacking food the same as backpacking food? Mostly the same foods, chosen more strictly. A backpacker can carry fresh food, tins and a heavier stove because the pace is slower and the pack bigger. On a fastpack, aim for an average of about 4.4 calories per gram or better, and favour food you can eat without stopping.

Which fastpacking foods cope with heat and cold? Chocolate softens in summer heat and turns hard in the cold, and cheese and salami sweat in warm weather, so eat them early in the trip. For Phoenix Bars, customers have reported both: one ate them around and below freezing on the Winter Spine Challenger South and said they stayed soft enough to eat, and another said they kept their shape in the heat of the Marathon des Sables.

How many Phoenix Bars should I take on a fastpack? The three-day plan above uses five, one or two a day, plus a spare: one as breakfast porridge and one in pieces on the move.

Should you stop to eat or eat on the move? Both. Eat little and often on the move to keep 150 to 400 calories an hour going in, the ISSN range for long efforts, and stop once or twice a day for food that needs a sit-down: wraps, cheese, a hot drink.

If you have a question about food for a particular route, email me at jfrost@flaming-phoenix.co.uk and I will answer it myself.

Sources: 2024 Adult Compendium of Physical Activities (walking and backpacking); McCance and Widdowson's Composition of Foods Integrated Dataset; NHS: understanding calories; Andrew Skurka: the 5,000-calories-per-day wilderness diet; ISSN position stand on ultramarathon nutrition (2019); Expedition Foods: Chicken Tikka with Rice; National Trails: South Downs Way; National Trails: Pennine Way; Walkhighlands: West Highland Way; Walkhighlands: Cape Wrath Trail.