Trail running nutrition: when to eat before a run and what to carry on UK trails

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

Quick answer: eat a light, mostly carbohydrate meal two to three hours before a trail run, which is the timing the British Dietetic Association gives for exercise. Runs under an hour need nothing during. Past two hours, aim for about 60g of carbohydrate an hour, starting in the first hour, and eat again soon after you finish.

This guide is for UK trail and fell runners, from a Saturday parkrun-plus-hills to a 50km trail race. It covers when to eat before a run, what to carry, how much per hour, and what fell race kit rules ask for. For 100 miles and multi-day races, see my guide to ultra running nutrition; for the hourly loop format, see backyard ultras in the UK.

When should you eat before a run?

Eat a light meal or a substantial snack two to three hours before a run that lasts over an hour or will be hard. The British Dietetic Association's sport fact sheet recommends a low-fat, high-carbohydrate snack or light meal two to three hours before exercise, because fat and fibre slow digestion and a full stomach does not mix well with a steep first climb.

Trail races make this awkward. Starts are early, venues are often a field an hour's drive from home, and nobody cooks in a car park. Here is how the timing works in practice, with foods that pack easily:

Timing is personal, so rehearse it on training runs. Lisa Nicholls, who used Phoenix Bars on the Machen Trail Marathon, found the same: "I initially find the bars challenging to digest so I have to eat one at least 2 hours before, but once it settles it works a treat." Denser food may need the full two hours; a banana needs much less.

Is it better to eat before or after a run?

Both, because they do different jobs. Eating before a long or hard run gives you carbohydrate to start with; eating after any long or hard run starts the refuelling, and the BDA advises starting "as soon as possible after exercise" when you train again soon. For an easy run under an hour, eating beforehand is optional and many runners prefer an empty stomach, but the meal afterwards still counts.

A common mistake runs the other way: an early start, no breakfast, a two-hour hilly run on nothing, and then a light lunch because the run "burned plenty already". Do that on consecutive weekends and the long runs get harder, not easier.

Does trail running burn more calories than road running?

Per hour, about the same; per kilometre, more, because trails are slower. The 2024 Adult Compendium of Physical Activities gives cross-country running 9.3 METs, the same as road running at 6 mph, and one MET is roughly one calorie per kilogram of body weight per hour.

The difference is time. For a 70kg runner, 9.3 METs is about 650 calories an hour (9.3 x 70 = 651). If a hilly trail half marathon takes you 2 hours 30 minutes against 2 hours on the road, the trail costs about 1,630 calories against about 1,300. Walking the steep climbs adds more time again. To estimate your own run, use the running calorie calculator.

How much should you eat during a trail run?

For runs over two hours, about 60g of carbohydrate an hour, rising towards 90g on ultras if you have trained your gut for it. Those are the figures in Asker Jeukendrup's review of carbohydrate intake during exercise (Sports Medicine, 2014), which also notes that slower, lower-intensity efforts need less.

On trail runs, start eating in the first hour, before you feel you need it, and eat little and often. A lot of runners can eat on the climbs, when they are walking with poles or hands on knees, and cannot face food on fast descents. Plan your eating around the climbs on your route.

Past three or four hours, sweet gels and sweets get hard to face for a lot of runners. That is when high calorie bars, a sandwich, salted nuts or whatever savoury food you can stomach take over. For the hour-by-hour version on longer races, see my guide to the best foods for ultra running.

What food should you carry on a trail run?

Carry food with plenty of calories per gram, because every gram in a race vest competes with waterproofs, a map and a head torch. This table compares common trail foods using per-100g values from McCance and Widdowson's CoFID dataset, scaled to a pocket-sized portion I chose for each; the Phoenix Bar row uses our own label.

Two things stand out. Nuts carry the most calories per gram but very little carbohydrate, so they help on a long, slow day more than in a race. And if carbohydrate per gram is all you care about, jelly sweets beat every bar on the list: 240g of carbohydrate for a four-hour run is about 300g of fruit gums, against about 430g of flapjack or at least 440g of Phoenix Bars. Most runners still want something that feels like food after a couple of hours, which is where a flapjack or a dense bar comes in. For more ideas, see my guides to calorie-dense foods and high calorie snacks.

What do fell race kit rules say about food?

The Fell Runners Association's requirements for runners list emergency food as part of the FRA Mandatory Minimum Kit for Long A, Medium A and Long B races, alongside waterproof whole-body cover, hat, gloves, map, compass and whistle. Organisers can ask for more, and it is at their discretion for shorter categories. The FRA does not set a calorie figure, but some trail race kit lists do, so read yours. Sabrina Amy, training for the Arc of Attrition, liked that "1 single bar meets the emergency calorie requirement of the essential kit list for my distance (c500kcal)". Emergency food is for emergencies: carry it in addition to the food you plan to eat.

What should you eat after a trail run?

A meal or snack with carbohydrate and some protein, as soon as you reasonably can. The BDA says to start refuelling "as soon as possible after exercise", especially if you train again within a day, and puts daily protein for endurance athletes at about 1.4 to 2.0g per kilogram of body weight, spread across the day. After a long fell run that might be a bacon or beans sandwich and a pint of milk in the café, or a bowl of pasta at home.

Long descents tend to leave the legs sorer after a hilly trail run than after the same distance on the road. If you do not feel hungry after a hard effort, which is common, eat something small and easy and have the proper meal later. My page on what to eat when your appetite is low has gentle ideas, and the ultramarathon recovery guide covers the days after a big race.

Where do Phoenix Bars fit for trail runners?

Phoenix Bars carry up to 557 calories in only 120g, with up to 66g of carbohydrate and up to 19g of protein. On a trail run that makes one bar about an hour's carbohydrate at 60g an hour. Runners use them three ways: as a breakfast two to three hours before the start, broken into pieces and eaten over an hour or two on the move, or stirred into hot water at a checkpoint or back at the car as a porridge. The six flavours are not sickly sweet, which helps once gels have lost their appeal. A dense bar can sit heavier than a gel, as Lisa found, so save it for the steadier parts of a run and use something lighter for the last fast mile. For the different ways to eat them, see how to use Phoenix Bars, or compare them with other options in the best energy bars for ultra running. If you want to try them, Phoenix Bars come in packs from six bars.

For longer events, the ultra-endurance and expedition nutrition guide covers multi-day eating, and the best ultra marathons in the UK lists the trail races to aim for next.

Frequently asked questions

How long after eating can I go for a run?

About two to three hours after a normal meal, and less after a small snack. The British Dietetic Association suggests a light, low-fat, high-carbohydrate meal two to three hours before exercise. A banana or a few jelly sweets can go in 30 to 60 minutes before if you are hungry; test anything denser on training runs first.

Should I eat before a morning run?

For an easy run under an hour, you do not have to: many runners go out before breakfast and eat afterwards. For a long or hard morning run, eat something light two to three hours before if you can, or a small, easily digested snack if you cannot face getting up that early.

Why do I feel sick eating during trail races?

Usually because of eating too much at once, eating fatty or high-fibre food while working hard, or trying something new on race day. Eat small amounts often, save chewier food for the climbs, and practise your race food on long training runs so your gut is used to it.

How much water should I carry on a trail run?

It depends on temperature, distance and where you can refill, so check the race kit list and the route. Some fell races have no checkpoints with water, so read the race details. On hot days drink to thirst at every chance you get, and carry enough to reach the next tap or stream you trust.

Do I need gels for a trail half marathon?

Not necessarily. If a trail half takes you over two hours, about 60g of carbohydrate an hour helps, but it can come from any food you can eat on the move: fruit gums, a banana, malt loaf or a flapjack work as well as gels for many runners.

Sources: British Dietetic Association, Sport and exercise food fact sheet; Jeukendrup A, A step towards personalized sports nutrition: carbohydrate intake during exercise, Sports Medicine 2014; 2024 Adult Compendium of Physical Activities, running; CoFID, McCance and Widdowson's composition of foods dataset; Fell Runners Association, requirements for runners 2025.