GR20 Corsica nutrition guide: how to fuel Europe's toughest thru-hike

Quick answer: On the GR20, plan to eat 4,500 to 6,000 calories a day. Refuge dinner and breakfast cover roughly 1,100 to 1,600 of that, so carry a day bag of about 300 to 500g of calorie-dense snacks, top up from refuge shops, and eat something every 45 to 60 minutes whether or not you feel hungry.

The GR20 is a 180km high-mountain traverse of Corsica with around 12,000m of elevation gain, split into 16 stages between Calenzana in the north and Conca in the south. Most hikers complete it in 14 to 16 days. Daily energy expenditure sits between 4,500 and 6,000 calories for a fit hiker carrying a 9 to 13kg pack across rocky, exposed terrain. The fuelling problem on the GR20 is not finding food. Every refuge has a small shop and a guardian-cooked dinner. The problem is calorie density, gluten and vegan availability, monotony after day three, and getting enough fuel into your body when heat and altitude blunt your appetite. This guide solves those four problems.

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

Quick facts: GR20 in numbers

The GR20 runs 180km from Calenzana to Conca with 12,000m of vertical gain, although tracked watch data from hikers including Karolina Tuszynska at Breaking the Borders shows total elevation change closer to 28,000m once descent is included. The trail is officially split into 16 stages, most around 10 to 15km, with 5 to 8 hours of effective walking per stage and ascents of up to 1,200m on the toughest day. The fastest times are now under 30 hours: François D'Haene ran it in 29 hours 46 minutes in July 2026, and Aurélien Dunand-Pallaz was reported to have lowered that to 27 hours 29 minutes in September 2026, which gives a sense of how compressed the calorie demand can become for fastpackers and trail runners. Refuges are staffed from mid-May to early October (16 May to 4 October in 2026), and most people walk between mid-June and mid-September.

Why fuelling decides whether you finish the GR20

Three things make food planning for the GR20 different from almost every other long-distance European trail.

The first is the consecutive nature of the load. The GR20 is up to sixteen hard days back to back, with no real rest, no taxi-accessible bailout for long stretches and granite underfoot that hammers your legs on every descent. Recovery happens overnight in a dormitory, eating whatever the refuge has prepared. If you under-eat on day two, you pay for it on day six. Most hikers who quit the GR20 quit somewhere between stages four and seven, and the pattern is consistent: a deepening calorie deficit combined with sleep debt and accumulated leg damage.

The second is the food environment. There are no grocery stores on the trail. Resupply is only fully possible at Asco Stagnu, Castel di Vergio, Vizzavona at the midpoint, and Bavella in the south. Refuge shops carry the basics: pasta, tinned tuna, cheese, biscuits, charcuterie, chocolate. Refuge dinners are typically Corsican soup, then pasta with sausage or lentils, then cake or cheese, paid for in cash at the refuge. They are honest, hearty meals that hit roughly 800 to 1,100 calories. They are also the same most nights, and pack weight pressure means most hikers carry only a day or two of food at a time. By stage four most people are sick of pasta. This is well documented across every major GR20 trail report, including TMBtent's guide and Tales of a Trail's resupply breakdown. The GR20 is not a place to assume you will magically want to eat. You won't, unless you have planned for it.

The third is the pack weight ceiling. Andrew McCluggage at Knife Edge Outdoor, who has covered the route extensively, recommends a maximum pack weight of 9kg for refuge-only hikers and 13kg for campers carrying their own shelter, including food and water. Every gram above that hurts you on the chains, ladders and slabs of the north. Calorie density per gram of pack weight is therefore the number to plan your food around. Bread is around 270 calories per 100g. Tuna is around 130 calories per 100g. Tinned sausage is around 250 calories per 100g. A Phoenix Bar carries up to 557 calories in a compact, 120g bar, about 4.6 calories per gram, and unlike refuge bread it does not go stale or need preparation.

For a wider primer on this kind of fuel-to-weight thinking, see our Ultra-Endurance and Expedition Nutrition Guide.

How many calories do you burn on the GR20?

A reasonable target for daily intake on the GR20 is 4,500 to 6,000 calories, depending on body mass, pack weight, pace and ambient temperature. Typical estimates put moderate hiking with a pack at 300 to 500 calories per hour, climbing toward 600 per hour on the steep, scrambling sections common in the GR20 north between Calenzana and Vizzavona. Most hikers move for 5 to 8 hours per day on the trail, with shorter active hours but higher intensity than something flat like the GR10.

Layer on basal metabolic rate (typically 1,500 to 2,000 calories for an adult), and you arrive at 4,500 calories as a floor and 6,000 as a realistic ceiling for stages with 1,000m or more of ascent. A useful internal benchmark: thru-hiker Hannah K. on the Pacific Crest Trail calculated 3,675 calories per day for 15-mile flat days at 75kg body weight. The GR20 has roughly double the vertical per kilometre, so the upper bound is higher.

Two physiological factors push your real intake below the calculated target.

Appetite suppression is the first. At altitude, levels of ghrelin (the hunger hormone) tend to fall while satiety signals rise, and several GR20 passes sit between 2,000m and 2,600m, where most walkers notice a mild effect. Heat compounds it: the GR20 in July hits 30 degrees in the valleys, and many walkers find they want less food on hot days.

The second factor is "food fatigue." When refuge dinners are 80 percent the same starch every night, intake drops even when calorie need climbs. Polar expeditions handle the same problem by rotating high-flavour, high-fat snacks in their day bags.

Our high calorie bars come in six flavours: Apple & Cinnamon, Cherry Bakewell, Chocolate, Vanilla, Salted Caramel and Ginger. Six rotations is enough to keep your palate moving for the duration of the trek. For more on flavour fatigue over multi-day efforts, our guide to calorie-dense foods for endurance and expeditions covers the science in full.

The refuge food problem solved

Every refuge serves dinner and breakfast in season. Refuge dinners average 800 to 1,100 calories and breakfast 300 to 500 calories, both paid for in cash at the refuge. That leaves a gap of around 3,000 to 4,500 calories per day that you have to provide yourself, almost all of which needs to be eaten while moving.

The conventional GR20 fuelling kit, distilled from the most-read trail reports, looks like this: bread, hard cheese (typically Corsican brebis or chevre), saucisson or charcuterie, biscuits, dark chocolate, dried fruit, energy bars, sweets. That works, with two catches. The bread is heavy and goes stale by day two, and the charcuterie sweats in heat above 25 degrees. Breakfast is thin too: many refuges offer little more than bread, jam and instant coffee.

I make Phoenix Bars, and one can stand in for a good part of that bag. Each one carries up to 557 calories in a compact, 120g bar, with gluten-free oats as the main ingredient. They are vegan and gluten-free, and they hold their shape in summer heat where chocolate melts and charcuterie sweats. The dense, gluten-free oat base also means each bar can be broken into a refuge cooking pot, mashed with water and eaten as a high-calorie porridge when heat or altitude has taken your appetite. For climbers and trekkers hiking with bars in heat, our note on how to use Phoenix Bars covers the porridge prep in detail.

For comparison shoppers, our wider analysis of high-calorie snacks for endurance benchmarks Phoenix Bars against the typical trail mix, gel and bar options you would otherwise carry.

Pack weight: the 9kg and 13kg rule

The two pack-weight ceilings widely accepted across GR20 guides are 9kg total for refuge stayers and 13kg total for campers, both inclusive of food and water. Water alone is 1 to 3kg per day on the GR20 in summer, depending on the heat and how exposed the next stage is. That leaves a tight envelope for food.

A practical day's food bag on the GR20, given a refuge dinner and breakfast, should weigh between 300 and 500 grams. At a realistic 4.5 to 5 calories per gram for a mixed bag of bars, nuts and dried fruit, that carries roughly 1,350 to 2,500 calories. Bread, fruit and tinned food fall well short of that, so the bag has to lean on nuts, chocolate and dense bars. Phoenix Bars carry about 4.6 calories per gram, more than a typical cereal bar at 3.5 to 4.0, and our guide to energy bars for hiking compares the wider field. Two Phoenix Bars a day (up to 1,114 calories in 240g) cover a good part of the gap between refuge meals; the same calories from baguette alone would weigh about 410g.

For trail runners and fastpackers attempting the GR20 in 5 to 10 days, the maths gets sharper. Our fastpacking nutrition guide covers the specific calorie-density thresholds for sub-10-day attempts, where you are eating almost entirely from your pack between refuges.

Stage by stage: where the calorie demand spikes

Stages 1 to 8 between Calenzana and Vizzavona are the hard half. Stage 2 from Ortu di u Piobbu to Carozzu involves the Spasimata footbridge and ladders. Stage 3 from Carozzu to Ascu Stagnu crosses Bocca Piccaia and a long, exposed traverse. Stage 4 from Ascu Stagnu to Tighjettu now climbs Monte Cinto's shoulder at Pointe des Éboulis (2,607m), the highest point on the trail since the Cirque de la Solitude was closed permanently after the 2015 rockfall. Stage 5, stage 6 and the Manganu to Petra Piana traverse all involve sustained scrambling. These are the days you want 5,500 to 6,000 calories and the energy density to actually carry it.

Stages 9 to 16 between Vizzavona and Conca are mostly easier on the body but longer in distance, with Monte Incudine (2,134m), the Aiguilles de Bavella, and the long final descent to Conca. The Bavella alpine variant is technical and not to be underestimated on tired legs. Calorie demand drops slightly to 4,500 to 5,000 on the average southern day, although the heat is usually worse south of Vizzavona which makes appetite the limiting factor rather than calorie need.

A simple rule that holds for both halves: eat something every 45 to 60 minutes on the trail, regardless of whether you feel hungry. By the time you feel hungry on the GR20 you are already in deficit. The 2016 joint position statement on nutrition and athletic performance from the American College of Sports Medicine suggests 30 to 60g of carbohydrate per hour for long exercise, rising to as much as 90g for the hardest, longest efforts, and walking pace sits towards the lower end. A Phoenix Bar carries up to 66g of carbohydrate, so one bar every two hours alongside other snacks keeps you in that range with little thought.

For broader hiking and trekking fuelling principles that apply across all multi-day routes, see our hiking and trekking nutrition guide.

North versus South: different fuelling strategies

The conventional north-to-south direction frontloads the technical difficulty. You arrive at the trailhead with full glycogen stores from carb-loading at home, then immediately spend three days scrambling. The risk is that you under-eat during the hardest section because your appetite has not adjusted to the workload. Pre-pack the first three days of trail snacks before you fly out. Shopping at the last minute in Calenzana tends to mean buying whatever looks comforting rather than what you planned.

Going south to north, the strategy is the opposite. You build up gradually through the southern half, your appetite catches up with your output by Vizzavona, and you hit the technical north already trail-fit and eating properly. Karolina Tuszynska at Breaking the Borders explicitly chose this direction for that reason on her 2023 thru-hike. The fuelling implication is that you can afford a lighter food bag in the first three southern days because your output is lower.

In both directions, Vizzavona is the natural resupply pivot. There is a Hôtel Monte d'Oro with a proper restaurant, a train station for bailout, and the only realistic full-restock point on the trail. Plan your bar carry around Vizzavona rather than trying to carry sixteen days from Calenzana.

What should you eat before starting the GR20?

Your muscles store roughly 1,500 to 2,000 calories of carbohydrate as glycogen, and a long first stage with 1,000m or more of climbing draws on it heavily. Starting with those stores full makes the hard northern days easier.

In the two or three days before you start, ease training right down and make easy-to-digest carbohydrate the base of every meal: oats, rice, pasta, potatoes, bananas and white bread. Avoid novel foods or anything unfamiliar to your gut. The morning of stage 1 in Calenzana, eat 800 to 1,000 calories at least 90 minutes before you start walking. For more on the carbohydrate-density side of this, see our breakdown of ultra high carb solid foods.

A practical daily fuelling template

Morning: refuge breakfast plus one Phoenix Bar broken into your pot with water, eaten as porridge before you leave the refuge. This loads roughly 800 to 1,000 calories before you walk a step.

On the trail: one Phoenix Bar plus a handful of nuts or dried fruit every two hours, with sips of an electrolyte drink between. Aim for roughly 30 to 60 grams of carbs per hour on the climbing stages.

Late afternoon arrival at the refuge: a snack within 30 minutes of stopping. Chocolate, biscuits, a third bar if you are hungry. Glycogen refills fastest in the first few hours after exercise, so eating soon after you stop helps when you have to walk again the next morning.

Evening: refuge dinner. Order it on arrival because they stop accepting orders mid-afternoon. Pair with one beer if you want, but follow with a full litre of water before bed.

A typical day on this template runs 4,800 to 5,500 calories, which is the right band for most of the GR20.

Heat, altitude, and the appetite problem

Two physiological factors specific to the GR20 will wreck your fuelling plan if you do not plan around them.

The first is heat. Daytime temperatures in the GR20 valleys hit 30 degrees from mid-July to late August. Many walkers find their appetite drops on hot days, and that is a normal response to heat, not weakness. The solution is liquid calories during the hot middle of the day. Bring electrolyte powder, mix it strong, and consider drinking your calories on the hottest stages. Honey, maple syrup or fruit purée sachets blended into water work. A Phoenix Bar broken up and mixed with water becomes a soft porridge that goes down when solid food won't.

The second is altitude. Multiple passes on the GR20 sit between 2,000m and 2,600m. Altitude blunts appetite, partly through changes in hunger hormones such as ghrelin and leptin. At 2,000 to 2,600m the effect is usually mild, but combined with heat and effort it pulls intake down. The defence is structured eating by clock, not by hunger. Every 45 to 60 minutes, something goes in.

What to pack: a calorie-dense food bag for the GR20

Calories per gram decide how heavy your day bag is. The table compares foods you can buy at refuge shops or bring from home, using typical values per 100g, so the figures are approximate.

Per day, between refuges, target a food bag of about 360g delivering around 1,700 calories. A worked example: two Phoenix Bars (240g, up to 1,114 cal), 50g of mixed nuts (50g, 290 cal), 30g of dark chocolate (30g, 170 cal), 30g of dried fruit (30g, 100 cal), one packet of electrolyte powder (10g, 50 cal), which comes to 360g and up to 1,724 calories. Plus the refuge breakfast (around 400 cal), trail-bought baguette and cheese for lunch (around 600 cal), and refuge dinner (around 900 cal) brings the day to roughly 3,600 calories, still short of a 4,500-calorie burn.

Scale up to three bars per day for the northern stages 2 to 6, and you cover the worst of the climbing without changing the structure.

For full sixteen-day carry planning, the Complete Bundle of 36 Phoenix Bars gives you just over two bars per day for the full GR20 with zero refuge dependence on bars. The Essential Bundle of 18 suits hikers who plan to use Vizzavona as a midpoint resupply. The Starter Bundle of 12 covers a single half (north or south).

Frequently asked questions

How many calories do you burn per day on the GR20? Most hikers burn between 4,500 and 6,000 calories per day on the GR20, depending on stage difficulty, pack weight and body size. The northern stages between Calenzana and Vizzavona, with around 1,000m of ascent and scrambling sections, sit at the upper end. Southern stages after Vizzavona average 4,500 to 5,000 calories.

Can you buy food on the GR20? Yes. Every refuge has a small shop selling pasta, tinned fish, cheese, charcuterie, biscuits, chocolate, bread and drinks. Larger resupply is possible at Asco Stagnu, Castel di Vergio, Vizzavona and Bavella. There are no grocery stores between refuges and no ATMs on the trail, so carry enough cash for the full traverse.

Is the GR20 suitable for vegans and gluten-free hikers? Refuge food is heavily pasta, cheese and Corsican charcuterie based, with very limited vegan or gluten-free options. Hikers on either diet need to carry their own backup food. Phoenix Bars are both vegan and gluten-free, with up to 557 calories in only 120g, which makes them well suited to filling the gap.

How heavy should my pack be on the GR20? Refuge-only hikers should aim for 9kg total including food and water. Campers carrying a tent should target 13kg maximum. Calorie density per gram of pack weight is one of the most important variables on a 16-day technical trek.

What is the best food for the GR20? The best GR20 food is calorie-dense, keeps in heat, suits your diet and is easy to eat when heat or altitude dulls your appetite. Hard cheese, saucisson, dark chocolate, nuts, dried fruit and Corsican biscuits all work and are sold at refuge shops. I make Phoenix Bars, which tick the same boxes and are vegan and gluten-free.

Do you need to book GR20 refuges? Yes. Under the 2026 rules, every night at a refuge must be booked online in advance, including bivouac pitches, and wild camping outside the refuge areas is not allowed. Refuges are staffed from 16 May to 4 October 2026, and meals and drinks are paid for on site in cash, so carry enough for the whole traverse.

Do I need to carry food for all 16 days? No. Every refuge has a shop and serves dinner. Most hikers carry one to two days of food at a time and top up at refuges or full resupply points. Carrying more than that wastes pack weight you cannot afford on the technical sections.

How do I avoid food fatigue on the GR20? Rotate flavours and textures. Refuge dinners are reliably pasta-based, so vary your day-bag snacks. Phoenix Bars come in six flavours which is enough rotation for a full sixteen-day traverse. The other lever is form: a bar eaten as porridge tastes different to the same bar eaten straight from the wrapper, which extends palate variety for free.

Should I take protein supplements on the GR20? Most hikers do not need protein supplements on the GR20 because refuge dinners deliver adequate protein from sausage, cheese and lentils. If you are vegan or gluten-free and skipping refuge meals, a small bag of plant protein powder is worth considering. Phoenix Bars carry up to 19g of plant protein each, so three a day add up to 57g.

Related guides

The GR20 sits within a broader category of multi-day mountain traverses that share similar fuelling logic. If you are planning the GR20, you may also find these useful: the Tour du Mont Blanc nutrition guide, which covers a comparable 170km Alpine traverse with similar refuge dynamics; the backpacking nutrition guide, which covers the foundational principles for any multi-day carry; and the trail running nutrition guide, which applies if you are attempting the GR20 fastpacking or going for a sub-10-day push.

For the broader fuelling philosophy underlying all of these, start with the Ultra-Endurance and Expedition Nutrition Guide.

Sources: American College of Sports Medicine, Academy of Nutrition and Dietetics and Dietitians of Canada, joint position statement on nutrition and athletic performance (2016); FFRandonnée, GR 20: ouverture des réservations pour la saison 2026; pack weights from Andrew McCluggage of Knife Edge Outdoor; elevation and direction notes from Karolina Tuszynska at Breaking the Borders; GR20 trail reports from TMBtent and Tales of a Trail; Phoenix Bar values from our own pack labels.