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2026-05-24 · 4 min read

Trail running nutrition — fueling strategy for long races

80% of DNFs in trail after km 30 are nutrition, not legs. Your legs can keep going; your gut stopped processing fuel, your blood sugar crashed, your calves cramped. Here's what matters, without the boring paper-citation routine.

The three levers

Every race of 3+ hours is won or lost on three levers:

1. Carbs per hour — 60 to 90 g/h in ultras, 30-60 g/h in shorter trail races.

2. Hydration + electrolytes — 500-750 ml/h, with 500-1000 mg of sodium/h in heat.

3. Pre-load — what you ate the 24 h before and on the morning of.

If one of the three fails, the other two won't save you.

Carbs: how much, how

Your body has reserves for roughly 90 min of intense exercise. After that hour and a half, you need exogenous carbs (what you eat).

| Race duration | Carb target |

|---|---|

| < 60 min | 0 — you don't need any |

| 60-90 min | 15-30 g/h optional |

| 90 min - 3 h | 30-60 g/h |

| 3-6 h | 60-90 g/h |

| > 6 h | 80-120 g/h (if the gut tolerates it) |

Fuel sources:

Gels: 20-25 g carbs in 40-60 ml. Fast absorption. Some have caffeine (for stretches when you need focus).

Isotonic drinks: 30-60 g/L of carbs. Two jobs at once: hydration + energy.

Solid food: oat bars, dates, jam sandwiches, salted potatoes. After hour 3+, the stomach asks for "real" food.

Gummies / candy: straight glucose, easy to chew and digest.

Pro tip: mixing sugar sources (glucose + fructose at a 2:1 ratio) lets you process more carbs per hour (up to 90 g/h vs 60 g/h with glucose only). Most modern gels come with this mix built in.

Hydration: simple math

Weigh yourself before and after a 90-min long run in conditions similar to race day. The difference, in kg, is your hourly fluid loss. Replace 70-80% during the race (not 100% — overflows the stomach).

Heat + altitude + hard effort: 750-1000 ml/h.

Temperate, moderate effort: 500-700 ml/h.

Cold and dry, easy effort: 400-500 ml/h.

When to add sodium:

Plain water past 1 h: hyponatremia (low sodium). Cramps, dizziness, confusion.

Sweat dries "white and sticky": you're a salty sweater, you need more sodium (1000+ mg/h).

Salt capsules: 1 capsule every 30-45 min in heat, on top of the sodium already in your gels and isotonic drinks.

Pre-load (the 24 h before)

The simple rule: maximize muscle glycogen without overloading the gut.

48 h before: start eating more carbs (pasta, rice, bread, fruit). Don't eat more fat or protein — just bump carbs.

24 h before: 8-10 g of carbs per kg bodyweight. For 70 kg = 560-700 g carbs across the day. Sounds like a lot — spread across 5 meals.

12 h before: dinner early (7-8 pm), carbs + a bit of protein, low fiber and fat.

3-4 h before the event: breakfast with 1-2 g carbs/kg. Oatmeal with honey + banana + coffee is the classic.

30-60 min before: nothing more, or one gel.

Train the gut

The gut trains like a muscle. If on your first 50K you want to take in 80 g carbs/h and you've never practiced it, you'll vomit at km 25.

How to train it:

1. First 4-6 weeks of your plan, on every long run >2 h, take in 40 g carbs/h. Force the food even if you're not hungry.

2. The next month, bump to 60 g/h.

3. Peak month, you hit 80-90 g/h.

The adaptation is called "gut training" and it's real science (Asker Jeukendrup documented it to death).

Race day

Hard rules:

1. Nothing new. What you ate in your long runs, you eat in the race.

2. Start eating at km 5-10. Don't wait until you're hungry — by then it's too late.

3. Set a timer every 30-40 min. The race distracts you; the timer reminds you.

4. Drink at every aid station, even if you're not thirsty.

5. If you're vomiting: stop 5 min, drop intensity, sip of Coca-Cola (yes, it helps), keep going slowly. Don't quit immediately.

Common mistakes

1. Gels only. After 4 hours your mouth and stomach want something solid. Pack a bar or dates.

2. Too much protein pre-race. Heavy feeling. Zero protein 12 h before.

3. Extra coffee. Diuretic + accelerates the gut. One coffee 90 min before, that's it.

4. Eating while climbing hard. The stomach won't process at HR 170. Eat on flats or descents.

5. Not tracking sodium. Salt caps are cheap and save races.

Vetta and nutrition

The [Vetta](/signup) engine flags your long sessions (>90 min or TSS >= 100) with suggested nutrition cards: target carbs/h, sodium, post-session recovery. It doesn't replace a sports dietitian, but it gives you the framework.