Endurance Nutrition
How to Fuel a 100-Mile Ultramarathon: Carbs, Calories, Electrolytes & Hydration
Oct
By Chase Hammond, Founder of Ultraverse Supplements and Ultraverse Races
Fueling a 100-mile ultramarathon is a different animal.
Depending on the runner and the race, 100 miles can mean anything from well under a day to 30, 36, or even 40+ hours of continuous movement. During that time your pace changes, the weather changes, your appetite changes, and what sounded great at mile 20 may make you want to puke at mile 70.
You are also going to burn far more calories than you can realistically replace. That’s not necessarily a problem. At ultramarathon intensities, your body uses a mixture of carbohydrate and fat for energy. Even if you’re consuming several hundred calories per hour, you may be burning considerably more than that. Your body’s stored fat helps make up much of the difference.
The goal of race fueling isn’t to replace every calorie you burn. It’s to keep enough carbohydrate, fluid and electrolytes coming in to support performance without overwhelming your gut. There is no magic number that works for every runner, but there are very good starting ranges.
How much should you eat during a 100-miler?
For many runners, a good place to start is:
- Carbohydrates: roughly 50–90 grams per hour
- Calories: roughly 150–400 calories per hour
- Fluid: based on thirst, conditions and individual sweat rate
- Sodium: based on sweat rate, fluid intake, weather and the rest of your nutrition
- Frequency: small, steady intake instead of huge feedings every few hours
These are starting ranges, not separate quotas: 50 grams of carbohydrate already supplies 200 calories. The most important part is finding an intake you can actually sustain for the duration of the race.
Eating 90 grams of carbohydrate per hour for three hours and then spending the next six unable to take in calories isn’t a very good fueling strategy. In ultrarunning, consistency usually beats perfection.
How many carbs per hour for a 100-mile ultramarathon?
Carbohydrate is the big one. For prolonged endurance exercise, 60–90 grams of carbohydrate per hour is a commonly recommended range, with approximately 90 grams per hour frequently recommended for very long endurance events. Some athletes may tolerate more, while others will perform better toward the lower end. [2]
For a 100-miler, though, there is another important question: Can your stomach handle that intake for 20, 30 or 40 hours?
That’s why gut training matters so much. If you want to race on 90 grams of carbohydrate per hour, don’t consume 25 grams per hour during every long training run and suddenly decide race morning is the time to triple it. Train your fueling just like you train your legs.
Calories per hour during a 100-miler
Carbohydrate contains four calories per gram, so the math is pretty simple:
| Carbohydrate | Calories from carbohydrate |
|---|---|
| 50 g | 200 |
| 60 g | 240 |
| 75 g | 300 |
| 90 g | 360 |
The International Society of Sports Nutrition recommends roughly 150–400 calories per hour during ultramarathon racing, with intake individualized according to the athlete, race duration and tolerance. [1]
You will almost certainly be burning more than that. Trying to replace every calorie you burn generally isn’t realistic and can create another problem by putting more into your stomach than it can process.
Your body also isn’t relying on carbohydrate alone. At the relatively low intensities common in ultramarathons, fat contributes substantially to energy production. Humans carry an enormous amount of stored energy as body fat compared with their limited carbohydrate stores. You are supplying carbohydrate to support performance while your body’s own fuel stores help cover the rest.
Start fueling early
One of the easiest mistakes to make in an ultra is waiting until you feel like you need calories. By the time you feel depleted, you’re already behind.
We would much rather see a runner establish a fueling schedule early and stay on it. That might mean drinking or eating smaller amounts every 15–30 minutes instead of waiting until an aid station and trying to hammer 600 calories at once. Boring and consistent works really damn well in ultrarunning.
Liquid fuel vs. solid food
Solid food absolutely can work in ultramarathons. A lot of runners use it successfully. But there is one thing we really like about liquid nutrition: control.
With a properly designed liquid fuel, you know exactly what you’re taking in. You know the carbohydrate, calories, sodium and concentration, and you can practice that exact same strategy repeatedly in training.
Solid food introduces more variables, especially at aid stations. A runner feels good, sees a bunch of food that looks great, and suddenly they’re eating quesadillas, cookies, bacon, chips, potatoes or something else they may never have eaten during a long run. Maybe it works. Maybe it doesn’t.
Fat, fiber, protein, serving size and food combinations can all change how something sits in the stomach, especially after many hours of running.
We’re not saying runners should never eat solid food. Plenty of people do very well with it, and during extremely long events some runners appreciate the flavor and texture variety. But if you’re going to use solid food, we strongly prefer that it be something you’ve actually tested. Race day shouldn’t become a 100-mile gastrointestinal experiment.
Why we like liquid fueling
Personally, for races of 100 miles or less, I prefer to fuel entirely with Proxima C. It’s easier on my gut, I know exactly what I’m getting every hour, and most importantly, I can recreate the exact same strategy over and over again during training.
That repeatability is a major advantage, particularly for athletes who have struggled with GI problems in the past. Instead of juggling water, gels, food, electrolyte capsules and whatever happens to be sitting on an aid-station table, you can build the majority—or even all—of your fueling around one predictable system.
That’s exactly the type of problem we designed Proxima C Ultra to solve.
How Proxima C Ultra fits into a 100-mile fueling plan
Each serving of Proxima C Ultra provides:
- 30 g carbohydrate
- 120 calories
- 250 mg sodium
- 85 mg potassium
- 30 mg magnesium
- 30 mg calcium
- 85 mg L-ornithine HCl
The carbohydrate blend contains 15 g Cluster Dextrin® and 15 g Palatinose™. That combination is intentional.
Palatinose is a slower-digesting, lower-glycemic carbohydrate than more rapidly absorbed carbohydrate sources such as maltodextrin. That means a smaller and more gradual blood glucose and insulin response.
Why does that matter in an ultra? Higher insulin levels tend to shift fuel use toward carbohydrate and suppress fat oxidation. In a controlled study of trained cyclists, consuming isomaltulose—the carbohydrate sold under the Palatinose brand—before exercise resulted in greater fat oxidation and lower carbohydrate oxidation during prolonged cycling compared with maltodextrin. [5]
That metabolic profile is one of the reasons we chose Palatinose as half of the carbohydrate blend in Proxima C Ultra. In a 100-miler, carbohydrate and fat are working together. You want to keep carbohydrate coming in, but your body’s enormous fat stores are also doing a lot of the work.
And the hourly math with Proxima C Ultra is extremely simple:
| Proxima C Ultra per hour | Carbohydrate | Calories | Sodium |
|---|---|---|---|
| 2 servings | 60 g | 240 | 500 mg |
| 2½ servings | 75 g | 300 | 625 mg |
| 3 servings | 90 g | 360 | 750 mg |
Two servings per hour
Two servings provide 60 g carbohydrate, 240 calories and 500 mg sodium. That puts a runner in a very practical range for many ultramarathons.
Three servings per hour
Three servings provide 90 g carbohydrate, 360 calories and 750 mg sodium. Now you’re at the upper end of the commonly recommended 60–90 gram carbohydrate range without needing to add gels, chews or food simply to hit your carbohydrate target.
That’s one of the biggest advantages of Proxima C Ultra: a runner can consume 90 grams of carbohydrate per hour entirely from the drink if that is what they train for and tolerate. The arithmetic establishes how much fuel it supplies; your training establishes whether that intake works for you.
Three servings also provide 750 mg of sodium, creating a predictable base that can be adjusted according to individual needs. Some runners will need more sodium. Some will need less. Some will drink more, and others will drink less. That’s why we don’t like pretending there is one perfect sodium number for every human being.
Practice the concentration you intend to race with, follow the product’s mixing directions, and adjust fluid intake to your needs. Don’t force extra fluid simply to reach your carbohydrate target.
Can you fuel a 100-miler completely with liquid nutrition?
Absolutely. For runners who struggle with GI issues, it’s something we think is worth considering. A carbohydrate-electrolyte drink can supply the carbohydrate, calories and electrolytes needed to make liquid nutrition either the foundation of a fueling plan or the entire fueling plan.
Many runners using Proxima C fuel their ultras primarily or completely with liquid nutrition. I personally prefer an all-liquid Proxima C strategy for races of 100 miles or less because it removes variables. I can train with exactly what I’m going to race with, and I know precisely how much carbohydrate, sodium and energy I’m taking in.
I don’t suddenly need to figure out whether eating half a grilled cheese sandwich at mile 78 is going to agree with me. Solid food is an option. It isn’t a requirement.
How much sodium do you need in a 100-miler?
This is where ultrarunning nutrition gets oversimplified very quickly. You’ll hear statements like “Every runner needs 1,000 mg of sodium per hour.” No.
Not every runner sweats the same amount. Not every runner loses the same amount of sodium in their sweat. Not every runner is competing in the same temperature, and not every runner is drinking the same amount.
Your sodium strategy depends on your sweat rate, sweat sodium concentration, temperature, acclimatization, pace, fluid intake and what else you’re eating or drinking. [1]
This is another reason we like having a predictable sodium base in Proxima C. Two servings provide 500 mg. Three provide 750 mg. From there, an athlete can adjust according to individual requirements.
What we don’t recommend is blindly swallowing salt simply because somebody told you that ultrarunners need a certain number of milligrams every hour. More isn’t automatically better.
Don’t confuse sodium with hydration
Exercise-associated hyponatremia is strongly associated with consuming excessive fluid relative to the body’s ability to get rid of it. Taking more sodium doesn’t magically make overdrinking safe. [4]
You should not be drinking enormous amounts of water simply because you’re afraid of becoming dehydrated. Let thirst guide drinking, and use conditions and what you’ve learned about your own sweat rate in training to inform your plan.
A runner crossing exposed terrain at 95°F can have dramatically different needs than the same runner moving through a cool night at 45°F. Your hydration plan needs to be adjustable.
Train your gut
This may be one of the most overlooked pieces of ultramarathon training. Your digestive system is trainable. Research on gut training suggests that repeated carbohydrate feeding during exercise can improve tolerance and may reduce gastrointestinal discomfort and carbohydrate malabsorption. [3]
If your race-day goal is 60, 75 or 90 grams of carbohydrate per hour, practice it. Don’t wait until race day.
Use long runs to test your carbohydrate intake, drink concentration, fluid intake and sodium strategy. Practice in the heat, in the cold, at night and during longer sessions when you’re tired.
Pay attention to what happens after six, eight or ten hours. Pay attention to what happens when you’re running harder than expected or when conditions change. The more variables you can eliminate before race day, the better.
That’s another reason we are big believers in repeatable liquid fueling. If it works in training, you can recreate it almost exactly on race day.
What if your stomach goes bad?
GI problems happen. Nausea, bloating, vomiting and stomach discomfort are common in endurance sports, and the causes can be complicated. The answer isn’t always simply, “My stomach can’t handle fuel.”
Ask what changed. Did you eat too much at once? Start drinking too much? Increase your pace? Get overheated? Eat something at an aid station you’ve never trained with? Combine several foods and products together? Make your drink much more concentrated than usual?
For mild stomach upset, sometimes the best move is simply to slow down, cool off, back intake down temporarily and give your stomach a chance to settle. What you want to avoid is turning a temporary stomach problem into five hours without calories. Once things begin to improve, start rebuilding your intake.
Persistent vomiting, confusion, a severe headache or worsening symptoms warrant assessment by race medical staff rather than simply changing your fueling.
A simple Proxima C 100-mile fueling strategy
Here is what this can look like in practice. This is an example, not a prescription for every athlete.
Option 1: 60 grams per hour
2 servings of Proxima C Ultra per hour provide 60 g carbohydrate, 240 calories and 500 mg sodium. For many runners, that may be a comfortable starting point.
Option 2: 75 grams per hour
2½ servings of Proxima C Ultra per hour provide 75 g carbohydrate, 300 calories and 625 mg sodium. Measure and portion your mix consistently so you know what you’re consuming across the hour. You can also combine Proxima C with another tested carbohydrate source if desired.
Option 3: 90 grams per hour
3 servings of Proxima C Ultra per hour provide 90 g carbohydrate, 360 calories and 750 mg sodium. For an athlete who has trained to tolerate that intake, this creates a simple system.
You know what goes into the bottle, you know what you need to consume, and you repeat it. That simplicity becomes increasingly valuable when you’ve been awake for 25 hours and your brain isn’t exactly operating at full capacity.
What we’ve learned from actually doing this
We’re obviously a supplement company, but Ultraverse isn’t a nutrition brand sitting on the outside of ultrarunning trying to figure out what runners do. Our team has graduate-level education and professional expertise in nutrition. I’m also an ultrarunner, and we create and direct ultramarathons ourselves.
That combination matters. We understand the science behind endurance nutrition, but we also spend race weekends watching hundreds of runners actually try to execute it through 100- and 200-mile events.
We see people absolutely nail their fueling. We also see runners get into trouble because they stop eating, eat things they’ve never trained with, drink far too much fluid, or allow a relatively small stomach issue to turn into a race-ending problem.
We also see runners execute simple, repeatable fueling plans hour after hour while everyone else is trying to figure out what sounds edible at the next aid station. That real-world experience has influenced the way we formulate our products.
Our philosophy is pretty simple: Give the athlete a predictable nutritional base. Make it easy to repeat. Train with it. Then remove as many unnecessary variables as possible on race day.
The biggest 100-mile fueling mistakes
Waiting until you’re hungry
Start fueling early. By the time you feel significantly depleted, you’re already playing catch-up.
Eating too much at once
Small, steady intake is generally easier to manage than giant aid-station feedings.
Trying new foods at aid stations
If you’ve never eaten it during training, mile 70 probably isn’t the best time to find out how your stomach handles it.
Underfueling because you’re afraid of stomach problems
Avoiding carbohydrate isn’t a very good solution either. Train your gut to handle the amount of fuel you intend to use.
Drinking according to a rigid schedule regardless of conditions
Your needs at noon may not be your needs at midnight.
Treating sodium like a magic pill
Sodium matters, but more isn’t always better, and salt doesn’t protect you from excessive fluid intake.
Making your fueling plan unnecessarily complicated
At some point you’re going to be exhausted. Simple systems are easier to execute when you’re tired.
Failing to practice the actual plan
If you haven’t trained it, you don’t really have a race-day fueling strategy. You have a theory.
Frequently Asked Questions
How many calories per hour should I eat during a 100-mile ultramarathon?
Approximately 150–400 calories per hour is a published ultramarathon starting range. Individual needs and tolerance vary, and you should not expect to replace every calorie you burn. [1]
How many carbs per hour should I consume during a 100-miler?
A practical range for many athletes is approximately 50–90 grams of carbohydrate per hour, with 60–90 grams being a common target for athletes who have trained to tolerate it. Test your target over long training sessions.
Can I get 90 grams of carbohydrate per hour from Proxima C Ultra alone?
Yes. Three servings provide 90 g carbohydrate, 360 calories and 750 mg sodium. Whether you can sustain that intake depends on your individual tolerance and training.
Can you fuel a 100-mile ultramarathon entirely with liquid nutrition?
Yes. Many ultrarunners do it successfully, including athletes using Proxima C. Liquid fueling is controllable and repeatable, which can make it useful for runners who struggle with GI issues or simply don’t want to depend on unpredictable aid-station foods.
Do I have to eat solid food during a 100-miler?
No. Some runners enjoy solid food and tolerate it very well. Others prefer primarily or entirely liquid nutrition. Solid food is an option, not a requirement.
Is liquid nutrition easier on the stomach?
It can be for some athletes, particularly when they have trained with the same product, concentration and hourly intake repeatedly. One of the biggest advantages is control: fewer unknown foods, fewer combinations and fewer changes from training to race day.
Why does Proxima C Ultra contain Palatinose?
Palatinose is a slower-digesting, low-glycemic carbohydrate. A controlled study in trained cyclists found greater fat oxidation and lower carbohydrate oxidation during prolonged exercise after consuming isomaltulose compared with maltodextrin. That metabolic profile is one reason we chose it as half of the carbohydrate blend in Proxima C Ultra. [5]
How much sodium do I need during a 100-mile race?
There isn’t one correct number for every runner. Your strategy should account for sweat rate, sweat sodium concentration, fluid intake, temperature and individual tolerance. Two servings of Proxima C Ultra provide 500 mg of sodium. Three provide 750 mg, giving runners a predictable base that can be adjusted if needed.
Should I practice my fueling plan before race day?
Absolutely. Your fueling strategy should be trained just like your legs. If you plan to consume 60–90 grams of carbohydrate per hour during the race, gradually practice that intake during long training sessions until you know what your stomach can handle.
Build a plan you can repeat
A good 100-mile fueling plan does not need to be complicated. Get enough carbohydrate, stay consistent, drink according to your needs and the conditions, have a sensible sodium strategy, train your gut, and eliminate as many race-day variables as you can.
That’s a huge part of why we created Proxima C Ultra. It gives an ultrarunner the ability to build a repeatable liquid fueling strategy around one product—with 90 grams of carbohydrate, 360 calories and 750 mg of sodium per hour at three servings.
Practice it. Dial it in. Then race with the same system you trained with.
Learn More About Proxima C Ultra →
Going beyond 100 miles? Read our complete guide to fueling a 200-mile ultramarathon.
About the Author
Chase Hammond is the co-founder of Ultraverse Supplements and Ultraverse Races. He has graduate-level education and professional experience in nutrition, is an ultrarunner himself, and creates and directs ultramarathons ranging from backyard events to 100- and 200-mile races.
His approach to endurance nutrition combines formal nutrition education with first-hand experience both as an athlete and as a race director watching hundreds of runners manage fueling, hydration and GI issues during extremely long events.
References
- Tiller NB, et al. (2019). International Society of Sports Nutrition Position Stand: nutritional considerations for single-stage ultra-marathon training and racing. Journal of the International Society of Sports Nutrition.
- Jeukendrup AE. (2014). A step towards personalized sports nutrition: carbohydrate intake during exercise. Sports Medicine.
- Martinez IG, Mika AS, Biesiekierski JR, Costa RJS. (2023). The Effect of Gut-Training and Feeding-Challenge on Markers of Gastrointestinal Status in Response to Endurance Exercise: A Systematic Literature Review. Sports Medicine.
- Hew-Butler T, et al. (2015). Statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, 2015. Clinical Journal of Sport Medicine.
- König D, et al. (2016). Substrate Utilization and Cycling Performance Following Palatinose Ingestion: A Randomized, Double-Blind, Controlled Trial. Nutrients.
