Trail Running Nutrition: Fuelling Long Hours on Feet
- Shrey Aggarwal
- 6 days ago
- 7 min read
Trail running burns more fuel per kilometre than road running because of climbing, and events run longer at lower intensity. That means fuelling by time not distance: carbohydrate every hour from the first hour, real food alongside gels on longer outings, and sodium when you're out past two hours or in heat.
Quick Overview
What makes trail running nutrition different from road running?
Gradient, duration and intensity, in that order. Running up a slope costs far more energy per metre covered than running on the flat: the metabolic cost of running rises from around 3.4 J per kg per metre on level ground to nearly 19 J per kg per metre at a 45% incline (Minetti et al., J Appl Physiol, 2002). You're moving slower and your watch shows fewer kilometres, but the fuel bill is much larger than the distance suggests.
The second difference is time. A 50km road race takes most amateurs four to five hours. A 50km mountain race with 2,000m of climbing can take eight, and that changes everything about how you plan food. Glycogen isn't running out at kilometre 30, it's running out at hour four, and the only sensible unit of planning is the hour.
The third is intensity. Trail and ultra pacing sits lower than road racing pace, which means fat contributes more of the energy and the stomach has more blood flow available to actually digest what you give it. That's the one thing trail running makes easier, and most runners waste it by under-eating anyway.
How many carbs per hour should you eat on a trail run?
Aim for 60 to 90g of carbohydrate per hour on anything over two and a half hours, and 30 to 60g per hour on shorter, easier outings. Those are the numbers in the joint position statement from the Academy of Nutrition and Dietetics, Dietitians of Canada and the American College of Sports Medicine, which caps intake at around 90g per hour once exercise runs beyond two and a half to three hours (Thomas et al., J Acad Nutr Diet, 2016).
Reaching the top of that range needs glucose and fructose together rather than a single sugar, which is why every gel and drink label now advertises a ratio.
Higher intakes are possible for trained guts. Elite mountain marathoners taking 120g per hour showed lower markers of muscle damage after the race than those taking 60 or 90g (Viribay et al., Nutrients, 2020), which is a useful finding but a poor starting point. Most trail runners I assess are eating closer to 35g per hour, and the gap between 35 and 70 is where their race is being lost, not the gap between 90 and 120.
Start eating in the first hour. On a six-hour day, a runner who begins fuelling at hour three is already 150g of carbohydrate behind and will spend the rest of the race trying to catch up on a stomach that no longer wants to cooperate.
The marathon fuelling numbers work differently, because a road marathon is short enough that you can partly ride out a deficit. Over eight hours you can't.
Real food or gels for long trail runs?
Both, and the longer you're out, the more the balance should shift towards real food. Ultramarathon runners consistently report that sweet liquid and gel-only strategies become intolerable after several hours, and mixed feeding with savoury and solid options improves total intake (Costa et al., IJSNEM, 2019). Palate fatigue is a real limiter on intake, and intake is the whole game.
What works, in rough order of how well it travels: boiled salted potatoes, rice balls, bananas, dates, jam or honey sandwiches, salted crackers, poha or upma in a small container for a crewed aid station, plain instant noodles at a night aid station, and gels for the climbs where chewing is impossible. Western States runners live on watermelon and broth. UTMB aid stations run on soup, cheese and bread. Hong Kong 100 runners take noodles. The pattern across every region is the same: something salty and warm keeps people eating when sweet things stop working.
Practise every single item in training. Race day is not where you discover that a particular gel gives you cramps at hour five.
How much fluid and sodium do trail runners need?
Drink to thirst, and treat sodium as a much smaller lever than the marketing suggests. Sweat sodium losses do vary enormously between people, from roughly 500 to over 2,000mg per litre, but there's remarkably little research testing whether replacing those losses during exercise changes any outcome that matters. Most of what athletes believe about salt comes from other athletes, coaches and electrolyte-brand marketing rather than from evidence (McCubbin, Performance Nutrition, 2025).
Where sodium does earn its place on a long trail day is in making drinks palatable enough that you keep drinking them, and in helping you hold onto the fluid you take in. Around 300 to 1,000mg of sodium per litre of fluid covers that job. Push much past 1,000mg per litre and palatability drops, and very concentrated doses draw water into the gut and produce exactly the nausea most runners blame on their gels (McCubbin, Performance Nutrition, 2025).
Salt tablets to prevent cramp are the weakest claim in the category. Studies of ultramarathon and Ironman fields have repeatedly failed to find that sodium intake, sweat sodium concentration or plasma sodium separates the runners who cramp from those who don't (McCubbin, Performance Nutrition, 2025). Cramp during long trail races is more often about pace and accumulated fatigue than about anything in your bottle.
Heat still changes the fluid side of the equation more than most runners expect. A 25km run in the Nilgiris in May and the same run in Scotland in October are different physiological events, and the plan should not be copied from one to the other. Weigh yourself before and after a few long runs in your typical conditions and you'll have a sweat rate to work from, which is worth more than any tablet. Our electrolytes explainer covers when the products are worth carrying and when they aren't.
Why does your stomach quit on long trail runs?
Because blood flow shifts away from the gut during prolonged exercise, and gastrointestinal symptoms affect 60 to 96% of ultra-endurance runners, making them one of the leading reasons people drop out of races (Costa et al., Aliment Pharmacol Ther, 2017). The two things that make it worse are dehydration and a sudden jump in carbohydrate intake the gut hasn't seen before.
The fix is training the gut like any other system. Take your race fuel on your long runs, at race intake rates, for eight to twelve weeks beforehand. Tolerance improves with repeated exposure, and the runners who arrive at a hundred-kilometre start line able to eat 80g an hour are the ones who spent a training block doing exactly that. Keep fibre low in the 24 hours before a long race, and keep caffeine moderate rather than stacking gels, tablets and coffee on top of each other.
What to eat before and after a long day on the trails
Eat a carbohydrate-based meal two to three hours before the start, low in fibre and fat, made of something you've eaten before a hundred times: oats, toast with jam, rice porridge, poha, a bagel, plain pasta. Then top up with 30g of carbohydrate in the 30 minutes before you start moving.
Afterwards, get food in once you're off your feet and your appetite returns, which on long mountain days is often an hour or more. Carbohydrate and protein together, in whatever form you'll actually eat: rice and eggs, dal and rice, pasta and chicken, a sandwich and milk. The urgency people attach to the first thirty minutes isn't supported by the evidence, and forcing food on a shut-down stomach usually backfires. What matters is total intake across the rest of that day and the next.
The Fueletics Perspective
Trail running punishes under-fuelling more slowly and more completely than any road event. The 10K runner who under-eats has a bad last mile. The trail runner who under-eats at hour two has six hours left to live with it, and it usually ends in a DNF or a walk.
The three variables that decide your day are carbohydrate per hour, fluid per hour, and sodium per litre. All three are individual, and all three are the sort of thing runners guess at for years without ever testing. If you'd rather have yours worked out from your sweat rate, training load and race profile than borrow someone else's plan, start with a Fueletics assessment.
Start with one change: eat something in the first hour of your next long run. Most people find the second half of the run is a different experience entirely.
FAQ
What should you eat during a trail ultra?
A mix of gels, drink mix and real food, totalling 60 to 90g of carbohydrate per hour once you're past two and a half hours. Savoury and solid options such as salted potatoes, rice, noodles and broth become more useful as the hours add up, because sweet flavours stop being tolerable.
How many calories per hour do trail runners need?
Most runners can absorb 240 to 360 kcal per hour from carbohydrate, which is the fraction that matters during the run. You will not replace what you burn on a long mountain day, and trying to do so causes more stomach problems than it solves.
Should you run fasted on trails to burn fat?
No, not for long runs. Fat already supplies a large share of energy at easy trail pace, and running long sessions fasted mostly reduces training quality and increases the risk of chronic under-fuelling.
How much water should you carry on a trail run?
Enough to drink roughly 400 to 800ml per hour in moderate conditions, more in heat, adjusted to the gap between water points on your route. Weigh yourself before and after a long run to get your own sweat rate rather than copying someone else's numbers.
Research References
Minetti AE, Moia C, Roi GS, Susta D, Ferretti G. Energy cost of walking and running at extreme uphill and downhill slopes. J Appl Physiol. 2002;93(3):1039-46. doi:10.1152/japplphysiol.01177.2001
Thomas DT, Erdman KA, Burke LM. Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. J Acad Nutr Diet. 2016;116(3):501-528. doi:10.1016/j.jand.2015.12.006
Viribay A, Arribalzaga S, Mielgo-Ayuso J, et al. Effects of 120 g/h of carbohydrates intake during a mountain marathon on exercise-induced muscle damage in elite runners. Nutrients. 2020;12(5):1367. doi:10.3390/nu12051367
Costa RJS, Knechtle B, Tarnopolsky M, Hoffman MD. Nutrition for ultramarathon running: trail, track, and road. Int J Sport Nutr Exerc Metab. 2019;29(2):130-140. doi:10.1123/ijsnem.2018-0255
Costa RJS, Snipe RMJ, Kitic CM, Gibson PR. Systematic review: exercise-induced gastrointestinal syndrome. Aliment Pharmacol Ther. 2017;46(3):246-265. doi:10.1111/apt.14157
McCubbin AJ. Sodium intake for athletes before, during and after exercise: review and recommendations. Performance Nutrition. 2025;1(1):11. doi:10.1186/s44410-025-00011-9
