Ultra Running Fueling Strategy: 50K, 50 Mi, and 100 Mi Nutrition

The first time I paced a friend at his 100-miler, I watched him run the first 50 miles on gels and Gatorade exactly like he'd run a marathon. At mile 62 he could not keep anything down. He DNF'd at mile 78, not because his legs were gone, but because his gut was empty and he was three thousand calories short of where he needed to be.

Ultra nutrition isn't a bigger version of marathon nutrition. It's a different problem.

What changes past hour three

1. The sugar ceiling drops

A trained gut absorbs 90 g/h of carbohydrate with a 2:1 glucose-fructose blend — for about 3 to 4 hours. Past that, gastric emptying slows, sucrose starts sitting in the stomach, and forcing more sugar causes nausea, burping, and eventually vomiting. This is not a training problem you can solve. It's physiology under prolonged stress.

Realistic ultra carb targets:

• 50K (4-7 h): 70-85 g/h for most runners
• 50 mi (8-12 h): 60-75 g/h
• 100K (11-16 h): 55-70 g/h
• 100 mi (18-30 h): 50-65 g/h, with dips in the night miles

2. Calories come from more sources

If you can only tolerate 60 g/h of carbs (240 kcal), but you need 280 kcal/h to not deplete, the gap has to come from fat and protein. Practically, that means solid food: boiled potatoes, peanut-butter tortillas, quesadillas, rice balls. A small amount of fat and protein adds calories without adding to the carb absorption load.

3. Sodium losses add up

Over 10-20 hours of sweating, cumulative sodium loss is enormous. Hyponatremia risk rises sharply past 8 hours if you're drinking a lot of plain water. Ultra sodium targets are 500-1000 mg/h — higher than marathon — and the lower end only applies in cool weather.

Distance-by-distance playbooks

50K (31 miles)

A 50K is the "just past marathon" ultra. Your gut is still mostly marathon-like; the main changes are one more feeding window and more sodium. Plan gel cadence for 70-80 g/h, then add one solid-food choice around mile 18-22 — something salty like a cheese stick, a few pretzels, or half a PB&J tortilla. This breaks up the sugar load and is your first practice run for longer ultras.

50 miles (80K)

The "first real ultra" distance. By mile 30 you're typically 4-5 hours in, and the gut will tell you when gels stop working. Common pattern: marathon-style gel cadence through ~mile 26, then a deliberate solid at every aid station (boiled potato, salted rice cake, quesadilla bite) plus continued sips of sports drink. Caffeine becomes useful around hour 6-7; 100-200 mg in a gel or a cola is standard.

100K

Longer aid-station stops and more night miles. Protein becomes a practical necessity — 5-10 g/h after hour five reduces muscle protein breakdown. Many 100K runners add a single serving of broth every 1-2 hours for warmth, sodium, and modest protein. The mental game starts mattering: fueling you resent eating now is fueling you won't take at mile 55.

100 miles

Half the problem is not bonking; the other half is not throwing up. Three principles:

1. Eat at every aid station after mile 20, even if it's just a cup of soup.
2. Warm broth + cold watermelon is the universal reset. When nothing else tastes good, that combination almost always goes down.
3. Two failure modes to watch: sugar fatigue (you can't look at another gel) and salt deficit (swollen fingers, muscle cramps, headache). Sugar fatigue is solved with real food; salt deficit is solved with capsules and salty food.

The gut training you should be doing

Treat your stomach like a muscle. Long training runs need to include real eating, not just sipped water. A few specific drills:

• Long-run fuel stacking: target 80-90 g/h on your longest training runs. Not every run — maybe one long run per week for 4 weeks during the race build.
• Solid-food simulation: take one "race food" on a long run (boiled potato, tortilla, rice ball) around the 3-hour mark. See what you tolerate.
• Heat rehearsal: if your race is hot, run at least two long runs in race-like heat with race-like fluid and sodium targets.
• Nighttime eating: for 100-milers, at least one long run in the dark with caffeine and your actual night-miles fuel plan.

Aid-station strategy

Every aid station after mile 15 needs the same three things:

1. Top off. Both bottles, every time. Running between stations underloaded is how deficits compound.
2. One warm, one cold. Broth + watermelon. Quesadilla + pickle. This keeps both options available as the weather and your mood shift across the day.
3. One salt action. Capsule, salty food, or sodium-heavy drink. Even in cool weather. Especially if you've been urinating clear every hour.

What goes wrong

Sugar fatigue

Happens around hour 4-6. You can't stand the smell of another gel. Solution: switch to savoury solids immediately — broth, potato with salt, quesadilla. Keep sports drink for fluid but pull the gel flavour.

Stomach shutdown (EIGS)

Exercise-induced GI syndrome. Blood diverts from gut to muscle, gastric emptying slows, sugar sits. Warning signs: burping gel flavour 20 minutes after taking it, nausea, feeling cold. Solution: slow down for 10-15 minutes. Drop to hike pace. Sip water only. Let the stomach clear before trying to eat again. Then restart with something mild — a cup of broth or plain rice.

Salt deficit

Muscle cramps, swollen fingers, headache, unusual irritability. Take 300-500 mg of sodium (1-2 caps plus a salty food). Feel better within 20-30 minutes — if you don't, reassess for hyponatremia (different problem, different fix).

Caffeine crash

Took 400 mg of caffeine at mile 30, now bonking at mile 45. Cycling caffeine prevents this. 50-100 mg every 2 hours during night miles, nothing during daylight unless you're mentally struggling.

Caffeine plan for 100-mile races

Race phase	Caffeine	Notes
Start to hour 6	0 mg	Normal morning coffee is fine
Hour 6 to 12	50 mg every 2 h	A caffeinated gel or 8 oz Coke
Night miles (dark)	100 mg every 2 h	Cola, a caffeinated gel, or a small 5-hour Energy split across two stations
Dawn + final quarter	100-200 mg	One-time boost for the finish push

Sample 100-mile fuel plan (16-20 hour finish, moderate weather)

Phase	Carbs/h	Sodium/h	Fluid/h	Notes
Miles 0-25 (h0-5)	70-80 g	500 mg	500 mL	Gels + sports drink. Easy pace. Front-loaded.
Miles 25-50 (h5-10)	55-65 g	700 mg	550 mL	Add solids. Broth at aid stations. First caffeine.
Miles 50-75 (h10-15)	50-60 g	800 mg	550 mL	Night miles. Caffeine every 2 h. Protein 8 g/h.
Miles 75-100 (h15-20)	45-55 g	700 mg	500 mL	Whatever goes down. Cola, chips, last caffeine.

Related

• Ultra Fueling Calculator — personalise the plan
• Gels vs Real Food — the transition in detail
• Running on Keto at Ultra Distance — alternative approach
• Post-Run Recovery Nutrition — the 24-48 hours after