100-Mile Ultramarathon Nutrition Plan: What to Eat, How Much, and When

At mile 70, your nutrition plan has to make sense to somebody who has been awake since before sunrise, is tired of chewing, and thinks half a cup of broth qualifies as dinner.

And that person is still you. Technically.

But a 100-mile ultramarathon nutrition plan has to survive much more than hunger. It needs to handle a full day of movement, darkness, temperature swings, nausea, sweet fatigue, missed aid stations, a pace that changes by several minutes per mile, and the very real possibility that your brain departments stop keeping accurate records.

For a 50-miler, you can often use one steady hourly plan from start to finish. The 50-mile ultra nutrition guide covers that approach. A hundred miler needs another layer: what you eat after normal dinner time, when caffeine becomes useful, how the crew keeps you from losing an hour at aid stations, and what happens when the food that worked for 12 hours suddenly becomes impossible to swallow.

So my boring answer is to start with measurable carbs, introduce familiar real food before you hate everything sweet, and make the overnight plan simpler than the daytime plan. You don't need a 30-hour tasting menu. You need enough options to solve predictable problems without turning every aid station into a hostage negotiation.

Start with an hourly target you can repeat

You will burn far more energy than your gut can replace during a 100-mile race.

But a 2025 case study measured two runners who each expended roughly 15,700-15,900 Kcal during a 161 km mountain ultramarathon. Both ate about half of what they burned, even though they finished in nearly 33 hours (Creer et al.). Two runners are not enough to establish a universal rule, but the size of that deficit explains the job: slow the drain and keep moving. Trying to eat back every calorie would bury most stomachs long before sunset.

The International Society of Sports Nutrition gives a broad ultramarathon range of 150-400 Kcal/h, with about 30-50 g/h of carbohydrate and 5-10 g/h of protein from tolerated foods (Tiller et al.). That guidance covers many race distances and athlete types, so I would treat it as guardrails rather than a perfect 100-mile formula.

And one small Western States study gives us a more specific clue. The six finishers averaged 0.98 g/kg/h of carbohydrate, compared with 0.56 g/kg/h among ten non-finishers. Finishers also consumed more total energy, fat, fluid, and sodium, especially early in the race (Stuempfle et al.). The sample was tiny and the result shows an association, not proof that eating more caused the finishes. Still, falling behind early probably doesn't make mile 80 more pleasant.

So for most runners, these are reasonable starting ranges to test:

Runner and experience	Carb target	Approximate energy from carbs
Smaller runner, sensitive stomach, first 100	40-55 g/h	160-220 Kcal/h
Most trained first-time 100-mile runners	50-70 g/h	200-280 Kcal/h
Experienced and well gut-trained	70-85 g/h	280-340 Kcal/h
Advanced athlete using mixed carbohydrate sources	85-90+ g/h	340-360+ Kcal/h, only if practiced

But that is a starting table, not a dare. A 52 kg runner and a 90 kg runner may settle on different numbers, and body size is only one part of it. Pace, heat, sex, menstrual symptoms, history of GI trouble, food preferences, and time on course all matter. Women should not automatically cut the carb target just because a chart was built from male-heavy research. Start with a tolerable absolute intake, practice it, and adjust from actual training evidence.

The best target is the one you can still hit after midnight.

Use numbers early, then let real food help

And gels and drink mix are boring in exactly the right way. A GU packet gives you a known amount of carbohydrate. A marked bottle of Tailwind or Maurten gives you another known amount. You can count both without asking a volunteer how much potato is hiding under the salt.

For the opening hours, I would keep most of the plan measurable: gels, chews, drink mix, applesauce pouches, or another low-fiber option you have used in training. Real food can join early, but it should support the carb total rather than replace it with vague snack math.

But then appetite starts changing.

So by late afternoon, salty and soft foods often become more appealing. Boiled potatoes, white rice balls, pretzels, broth, a small piece of quesadilla, white bread with honey, noodles, or a few bites of an Uncrustable can break up the sweetness. The ISSN position stand notes that preference for savory food tends to increase as ultramarathons get longer, which fits what most aid-station tables are already telling us (Tiller et al.).

But real food comes with tradeoffs. Fat, fiber, and protein slow digestion, and large servings take more gut work while blood flow is being pulled toward working muscles and skin. You do not need to ban them. Keep portions small, use foods you have tested, and remember that a cheese quesadilla may be comfort food without being a particularly efficient carbohydrate delivery system.

Here is a practical rotation:

Race period	Measurable base	Useful supporting foods
Hours 0-6	Gels, chews, drink mix	Banana, applesauce, small rice ball
Hours 6-12	Keep at least half the carbs measurable	Potatoes, pretzels, white bread, small wrap
Hours 12-18	Liquid or soft carbs become more useful	Broth, noodles, rice, mashed potato, cola
Hours 18-finish	Whatever remains countable and tolerable	Gel, drink mix, broth, applesauce, small familiar bites

Do you have to switch to real food? No. Plenty of athletes use gels and liquid carbs for most of a hundred. If that is what your stomach accepts, good. The mistake is assuming that because ultras offer pancakes and bacon, your gut will suddenly want brunch while climbing at 2 a.m.

Need exact race-day numbers? Build your personalized carb, fluid, and sodium plan in about 60 seconds: Use the free EnduranceOS planner.

What the day and night can look like

A schedule should reduce decisions, not create 30 different alarms.

For a runner aiming near 24 hours, one workable plan might start around 60-70 g/h, use a mix of sweet and savory foods after six hours, and move toward softer options overnight. A 30-hour runner may use a slightly lower hourly target if that is what training supports, but the longer time on course makes consistency even more important. Ten missed grams each hour becomes 300 g across 30 hours.

Example for a roughly 24-hour finish

Race time	Target	Example execution
Hours 0-4	60-70 g/h	Two gels with water, or one gel plus measured sports drink
Hours 4-8	60-70 g/h	Drink mix and gel, with banana or potato for variety
Hours 8-12	55-70 g/h	Measurable base plus rice, pretzels, or a small wrap
Hours 12-18	50-65 g/h	Broth or noodles, applesauce, gel, drink mix, planned caffeine
Hours 18-24	45-65 g/h	Soft or liquid carbs, cola if counted, small salty bites

Example for a roughly 30-hour finish

Race time	Target	Example execution
Hours 0-6	50-65 g/h	Gels, drink mix, chews, small familiar food
Hours 6-12	50-65 g/h	Same base with potato, rice, pretzels, or white bread
Hours 12-18	45-60 g/h	Smaller servings, broth, noodles, applesauce, drink mix
Hours 18-24	45-60 g/h	Overnight caffeine window, soft carbs, counted cola
Hours 24-30	40-60 g/h	Simplest tolerated options, taken on a written schedule

These examples deliberately allow the target to soften late. Some trained runners can hold 70-90 g/h for the entire race, and that is a useful advantage if they have earned it. Others protect total intake better by dropping from 65 to 50 g/h instead of forcing one more dense bottle, becoming nauseated, and taking in nothing for two hours.

The schedule is also allowed to flex with terrain. Eat the chewy food on a long hike, not before a hard descent. Take a gel before the exposed climb rather than halfway up it. Refill and reset at crew access, then leave. Your average over the hour matters more than taking every bite at an exact minute.

The overnight problem is mostly logistics

Darkness changes the race even if your calorie target stays the same.

Temperatures fall, pace slows, hot food sounds better, and sleepiness can make a normal task feel oddly complicated. In a study of 1,154 mountain ultramarathon finishers, sleep-deprivation symptoms were common, including reported falls and hallucinations. Many of those races lasted longer than a typical 100-mile event, but the point still applies: an overnight runner needs a plan for alertness, not just calories (Kishi et al.).

Put the easiest foods in the easiest pockets. Label the nighttime drop bag in giant letters. Carry a backup headlamp where somebody can reach it without unloading the whole vest. And make the food list shorter after dark: perhaps one liquid carb, one gel, broth at selected aid stations, and one savory backup.

Warm food is useful because it can solve temperature, texture, and morale at once. But "I will eat soup at night" is not enough. Find out what the race serves, estimate the carbs in a cup, and decide what measured fuel goes beside it. Broth may supply fluid and sodium while barely touching the carbohydrate target.

The night can turn into survival of the fitness surprisingly fast, so the plan should get simpler as your thinking gets worse.

Save caffeine until it has a job

Caffeine can improve endurance and alertness, including under sleep-deprived conditions, but more is not automatically better. The ISSN position stand finds the most consistent performance benefit around 3-6 mg/kg, notes that effects differ substantially between athletes, and warns that very high doses add side effects without being necessary (Guest et al.).

In a small randomized study, repeated 2 mg/kg doses improved running and cognitive performance during a night of total sleep deprivation (Khcharem et al.). That was a controlled experiment with 12 recreational runners, not a 100-mile race, so I would not copy its dosing schedule blindly. It does support the basic idea that caffeine can be saved and used during the overnight window instead of spending the whole budget before breakfast.

For most runners, I would plan caffeine by job:

• normal coffee before the start only if it is already routine
• little or no added caffeine through the early hours
• a measured dose near dusk or the first real drop in alertness
• smaller follow-up doses overnight if practiced and still within the planned total
• no random stacking of caffeinated gels, gum, cola, coffee, and energy drink

Count everything. A caffeinated GU, Clif Bloks, Coke, coffee, and caffeine gum all land in the same total even when the wrappers pretend they have never met.

Body size matters here. 3 mg/kg is 165 mg for a 55 kg runner and 270 mg for a 90 kg runner. Sensitivity, habitual intake, anxiety, heart rhythm concerns, medications, and the need to drive after the race matter too. The caffeine timing guide covers the dose math in more detail.

Your crew should run the checklist

A good crew does not need to invent solutions at every checkpoint. They need a short list and permission to keep you moving.

Give them a one-page sheet with expected arrival windows, the fuel target, bottle concentration, sodium plan, caffeine timing, clothing changes, and medical red flags. Put the race's aid-station rules on it too. Some events restrict crew access, outside assistance, or where pacers can join, and the current athlete guide gets the final word.

At each crew stop, the questions can stay basic:

1. What did you eat in the last hour?
2. Are you drinking normally, unusually thirsty, or feeling bloated?
3. Any nausea, vomiting, confusion, dizziness, or trouble coordinating?
4. What are you carrying to the next stop?
5. Which one problem are we fixing before you leave?

That last question matters. Changing shoes, adding a jacket, eating six foods, drinking a full bottle, taking caffeine, and sitting for ten minutes is not a reset. It is an entire board meeting.

Pack drop bags by purpose instead of by hope:

Bag	What belongs in it
Day refill	Counted gels, drink mix packets, familiar solid food, spare flask
Dusk	Headlamp and backup battery, warm layer, measurable fuel, first planned caffeine
Overnight	Broth or soft-food option if allowed, dry gloves, simple carbs, stomach backup
Final section	Easiest tolerated fuel, spare light, weather layer, small caffeine option if planned

Use clear bags inside the main bag, label every drink packet by bottle size, and write the carbohydrate amount on homemade food. Tired you should not have to remember whether the rice ball has 15 g or 35 g.

Hydration and sodium still follow your sweat

The race may last a full day, but your body does not suddenly need a universal gallon schedule.

The ISSN ultramarathon guidance suggests roughly 450-750 mL/h of fluid as a broad starting range (Tiller et al.). Cool nighttime hours may require less. Hot exposed sections may require more, especially for a runner with a measured high sweat rate. Use repeated training measurements, drink according to thirst and conditions, and avoid gaining body weight from overdrinking.

Sodium should be tied to fluid intake, sweat rate, sweat sodium, weather, and sodium already coming from food. Broth, sports drink, SaltStick capsules, gels, and pretzels all count. The sodium-per-hour guide explains why mg/L and mg/h are different numbers, while the sweat-rate guide helps set the fluid side.

And sodium does not cancel excessive water. Exercise-associated hyponatremia is mainly associated with drinking beyond losses, and a sports drink can still contribute when total fluid intake is too high. Smaller runners and slower finishers deserve extra caution because they have more hours to accumulate an error. Read the hyponatremia guide before building an aggressive fluid schedule.

Confusion, severe headache, repeated vomiting, unusual swelling, loss of coordination, chest pain, or worsening dizziness need race medical help. Do not diagnose the problem from a folding chair and answer every symptom with more water, salt, or caffeine.

When your stomach starts making decisions

GI trouble is common enough in a hundred that it deserves a written backup plan.

At the 161 km Western States Endurance Run, 96% of surveyed runners reported at least one GI symptom. Among finishers, 43.9% said GI symptoms affected performance, and among non-finishers, 35.6% listed them as a reason for dropping. Nausea was the most common serious complaint (Stuempfle and Hoffman).

That does not mean vomiting is inevitable. It means "I'll just eat whatever sounds good" is a weak Plan B.

If nausea starts, slow the effort, get cool if heat is part of the problem, and stop stacking dense carbs on top of a sloshy stomach. Small sips and a short pause from concentrated fuel may help while you reassess. Once things settle, restart with a small familiar carb dose rather than trying to repay the entire deficit in one aid station.

Use the symptoms as information:

What you notice	What to check first
Sloshing and bloating	Fluid rate, drink concentration, pace, overdrinking
Sweet foods suddenly feel impossible	Switch texture and flavor, keep carbs measurable
Reflux or heavy stomach	Portion size, fat, fiber, protein, running intensity
Nausea in heat	Pace, cooling, fluid balance, and medical warning signs
No appetite but clear thinking	Use smaller liquid or soft-carb doses on schedule

The goal is to resume intake, not punish your gut. The race stomach-problems guide goes deeper into pacing, heat, concentration, and gut training.

Practice the boring parts before race week

One six-hour long run cannot test a 24-hour plan, but a training block can test every component.

Practice the daytime base on ordinary long runs. Test real food while hiking uphill. Use an evening run to learn whether broth, cola, or a caffeinated gel feels different after dinner. Run with the headlamp, open the same zipper with cold hands, mix the drink packet without kitchen scissors, and eat after several hours when you are no longer excited about training nutrition.

Shorter runs count too. A 45-minute easy run can test a gel flavor, bottle concentration, or whether a chew turns into dental work in cold weather. The gut-training guide explains how repeated carbohydrate practice can improve tolerance.

Do at least one race-simulation block that includes dusk or darkness. It does not need to become an unsafe sleep-deprivation stunt. Start late enough to practice lighting, clothing, caffeine timing, crew instructions, and the foods assigned to the overnight bag. Then recover properly.

Your final plan should fit on one page:

• hourly carbohydrate range
• fluid range for cool, normal, and hot conditions
• sodium already supplied by food and drink
• caffeine products, doses, and earliest planned time
• crew and drop-bag locations
• the foods that solve sweet fatigue
• the backup when nausea starts
• symptoms that mean stop and seek medical help

If the plan takes ten minutes to explain while sitting at the kitchen table, mile-80 you is not going to run it.

Keep the numbers countable, the food familiar, and the nighttime choices short. A hundred miles will create enough surprises without letting the aid-station buffet write the strategy.

The EnduranceOS planner builds a personalized, hour-by-hour carb, fluid, and sodium plan from your body, expected finish time, and race conditions. It takes about 60 seconds, and it's free.

This article is educational and is not medical advice. Athletes with diabetes, kidney or heart conditions, GI disease, a history of hyponatremia, or medications that affect fluid balance should discuss ultramarathon fueling with a qualified clinician.