Most hikers under-fuel by a dramatic margin. You can burn 400–600 calories an hour on a loaded ascent, yet many people eat like they are sitting at a desk. By late afternoon the wall hits: shaky legs, blurred focus, a sudden hatred of the trail. This guide explains what your body actually burns, how much water and salt you lose, and how to build a fueling rhythm that prevents the bonk before it starts.
1. How your body burns energy on the trail
Exercise physiologists measure effort in METs (Metabolic Equivalents). One MET is the energy you use sitting quietly — roughly 1 kcal per kilogram of body weight per hour. Multiply your weight in kg by the MET value of the activity, then by hours, and you get a rough hourly burn.
| Activity | MET | Hourly burn (70 kg person) |
|---|---|---|
| Easy stroll / flat trail | 4.3 | ~300 kcal/h |
| Moderate hiking | 5.5 | ~385 kcal/h |
| Brisk hiking | 6.0 | ~420 kcal/h |
| Backpacking (loaded) | 7.0 | ~490 kcal/h |
| Heavy pack / steep ground | 8.5 | ~595 kcal/h |
| Scrambling / snowshoeing | 9.0 | ~630 kcal/h |
Over an 8-hour day with a heavy pack, that is 3,500–4,500 kcal just from movement, on top of your ~1,500 kcal basal metabolism. Total daily needs on a big trip often reach 4,000–5,000 kcal.
2. How much to eat: per hour and per day
The golden rule of endurance fueling is do not wait until you are hungry. By the time hunger signals arrive, you are already behind. Aim to take on roughly 200–300 kcal every hour while moving, starting within the first hour on the trail. That works out to a small snack every 30–45 minutes rather than one big lunch.
Across the full day, plan for 2,500 kcal as a minimum on an easy day and 3,500–4,500 kcal on a hard, cold or high-altitude day. Cold weather raises your burn further because your body spends energy staying warm.
3. What to eat: the macronutrient mix
On the move, your body runs fastest on carbohydrate, which digests quickly and feeds working muscles directly. A working ratio for trail food is roughly 45–55% carbs, 30–35% fat, and 15–20% protein. Carbs keep you moving; fat provides dense, slow energy; protein protects muscle over multi-day trips.
- Breakfast: oats, dried fruit, nuts — slow carbs plus fat to start steady.
- On-trail snacks: energy bars, gels, dried fruit, candy, nut butter packets. Fast carbs.
- Dinner: a hearty dehydrated meal or rice/pasta with protein, plus a hot drink.
4. The hydration rhythm
Thirst lags behind dehydration. By the time you feel thirsty, you have already lost 1–2% of your body weight in fluid, and performance drops. Drink on a schedule rather than by feeling: about 0.5–0.75 litres every hour in cool weather, rising to 1 litre or more in heat or steep climbing.
Urine color is your free dashboard. Pale lemonade means you are hydrated; dark apple juice means drink now. Weigh yourself before and after a long training hike: for every kg lost, drink 1–1.5 litres to recover.
5. Electrolytes and salt
Water alone is not enough. Sweat carries sodium, potassium and magnesium. If you drink large volumes of plain water without replacing salt, you risk hyponatremia — low blood sodium, which feels alarmingly like exhaustion and can be dangerous.
| Condition | Sodium to replace | Practical action |
|---|---|---|
| Cool day, light sweat | ~200–400 mg/h | Normal trail food is enough |
| Warm day, steady pace | ~500–800 mg/h | Salty snacks or one electrolyte tab |
| Hot, heavy sweat, long day | ~800–1,200 mg/h | Electrolyte drink + salty meals |
6. Fiber, gut tolerance and what to avoid
Long days on the trail are not the time to experiment with new foods. Your gut already has to digest heavy, sweet snacks while blood flow is diverted to your working muscles, so avoid high-fiber, greasy or gas-producing foods that you rarely eat at home. Beans, raw cruciferous vegetables and heavy dairy are the classic culprits. Most hikers find that familiar, slightly sweeter and lower-fiber foods digest best when they are working hard.
Pre-hydrate the evening before and the morning of. Drink roughly half a litre at breakfast, and eat a real meal — not just coffee. Starting already dehydrated or fasted puts you behind before the first climb, and you can never fully catch up on the move.
7. Preventing low blood sugar
Low blood sugar (hypoglycemia on the trail) happens when you burn through stored carbs faster than you eat. Three habits prevent it: start eating within the first hour, never skip the mid-morning and mid-afternoon snacks, and keep fast sugar (gels, candy) accessible in a hip-belt pocket, not buried at the bottom of the pack. Practice your fueling plan on training hikes, not on day one of a remote trip. If you feel the warning signs described above, do not wait for the group to agree — stop, sit, and fuel now.
Calculate your exact fuel needs
The Calories & Hydration tool estimates your burn, water and electrolyte needs from weight, weather and pack load — and the Food Planner turns that into a day-by-day shopping list.