Here is a number that should bother you: the average ultra runner takes in about 37 grams of carbs per hour during a race.1 Researchers who observed runners in real time during a 120 km race found actual intake ranged from just 22 to 63 grams per hour.3 The recommended amount is 60 to 90 grams per hour. Most runners are not even close.
Researchers have measured this gap repeatedly. Most runners think they are eating enough. Most runners are wrong. And it costs them.
"Only one [runner] achieved the benchmark recommendations for carbohydrate intake during endurance exercise."Costa et al., British Journal of Nutrition, 2014 — study of ultra-endurance runners during a 24-hour event
Why This Matters
Your body can store about 90 to 120 minutes of fuel as glycogen in your muscles and liver. After that, if you are not eating, your body starts to break down muscle for energy. You slow down, your thinking gets cloudy, and your gut starts to rebel.
A study of the Western States 100-Mile Endurance Run found a clear pattern. Finishers consumed significantly more calories, carbohydrates, fat, and sodium than non-finishers at every point in the race.2 Finishers averaged roughly 70 grams of carbs per hour. Runners who dropped out averaged less than 45 grams. The difference was not fitness. It was food.
In longer races, the gap is even bigger. A 2025 study measured the energy balance of runners across multiple ultra distances and found a mean deficit of nearly 6,800 calories per race. Runners at the 100-kilometer distance consumed about one-third of the calories they burned. Even at 230 kilometers, where runners move much slower and have far more time to eat, they still consumed less than half of what they burned.8 A complete match is impossible during a race. But the runners who come closest finish more races.
A 2024 study tracked runners during a 100-mile trail race using continuous glucose monitors. Faster finishers not only ate more carbs per hour, they also had more stable blood sugar throughout the race. The slower finishers had glucose swings more than 14 mg/dL wider on average. The researchers found a direct link: the more your blood sugar fluctuates, the slower you run.5
Here is why that matters. The fatigue you feel late in a race is not just your legs giving out. Your brain monitors blood sugar at all times. When it starts to drop, your brain sends a signal to slow down. This happens long before your muscles actually run out of fuel. A 2026 review of decades of endurance research confirmed that preventing this blood sugar drop, not refilling muscle glycogen, is the primary reason eating during exercise improves performance.7
"Fatigue appears to be a brain-control mechanism designed to cause exercise termination before irreversible energy depletion."Noakes et al., Endocrine Reviews, 2026
Why Runners Under-Eat
There are a few reasons this happens, and none of them are about not caring.
Your stomach shuts down
When you run hard, blood moves away from your gut and toward your legs. This slows digestion and makes food less appealing. Many runners wait until they are hungry to eat. By then, they are already in a hole that takes 30 to 45 minutes to climb out of.
Appetite also collapses as a race goes on. A 2025 study found that only 12.5 percent of runners reported reduced appetite before the race. By the time they finished, that number had risen to 73 percent.8 Your hunger signals become least reliable exactly when fueling matters most.
Race excitement overrides your body signals
The first few hours of a race feel great. You are not tired, you are not hungry, and eating feels unnecessary. Runners who skip fueling in the first half almost always pay for it in the second half.
Nausea shuts fueling down
GI distress is the norm, not the exception. Research on the Western States 100-Mile Endurance Run found that 96 percent of runners experienced GI symptoms, and 44 percent said it directly hurt their race.4 Nausea alone is one of the most common reasons runners stop eating entirely.
But nausea during an ultra has several possible causes. Low blood sugar is one. Insufficient electrolytes are another. When sodium drops too low, nausea often follows. Too much fat or fiber during a hard effort, heat, and dehydration can all play a role too.
The mistake is assuming nausea means you ate too much. More often it means something is missing: calories, sodium, or fluids. Trying a small gel plus an electrolyte tab or some broth is usually worth attempting before you stop fueling altogether.
If you feel nauseous during a race: don't assume it's too much food. Low blood sugar and low electrolytes are both common causes. Try a gel plus an electrolyte tab or some broth, and give it 10 to 15 minutes before you stop fueling altogether.
How Much You Actually Need
Carbs should make up the bulk of your race calories. In the 2025 John et al. study, roughly 79 percent of all calories consumed during ultra events came from carbohydrates.8 Fat and protein played a supporting role, but carbs were the engine.
The target range is 60 to 90 grams of carbs per hour for most runners. If you are moving fast or climbing a lot, lean toward the higher end. If you are hiking or in the back half of a long race when your pace has slowed, 60 grams per hour is a reasonable floor.
To hit 60 grams per hour, you need to eat something roughly every 20 to 30 minutes. A standard energy gel has about 22 to 25 grams of carbs. That means two to three gels per hour, or the equivalent in other foods.
| Food | Carbs | Notes |
|---|---|---|
| Energy gel (standard) | 22–25g | Easy to carry, fast absorbing |
| Energy gel (high-carb, e.g. PF90) | 40–90g | Fewer servings needed per hour |
| Banana (medium) | 27g | Easy on the stomach, available at most aid stations |
| Boiled potato (100g) | 17g | Salt helps; great for later miles when gels feel heavy |
| Broth + crackers | 10–15g | Mostly sodium; supplement, not replace carbs |
| Target per hour | 60–90g | Start eating in the first 30 minutes, not when hungry |
The Rule That Changes Everything
Start eating before you are hungry. Set a timer on your watch for every 20 to 25 minutes. When it goes off, eat something. Do not wait for hunger. Do not wait until the next aid station if that is 45 minutes away. Eat on schedule.
This feels strange at first. In the early miles, you will eat when you do not feel like eating. That is correct. You are not fueling how you feel right now. You are fueling for mile 60.
Build up gradually
Your gut can be trained to absorb more carbs per hour. Most people start at 30 to 45 grams per hour and work up over 6 to 8 weeks of practice on long training runs. Start low, add 10 grams per hour every few weeks, and practice eating at race effort, not just on easy days.
Mix glucose and fructose
Glucose is the sugar your blood actually carries. When you eat carbs, your body breaks them down into glucose and sends it into your bloodstream. Fructose is a different sugar, found naturally in fruit and added to many gels and chews. Your body processes fructose separately, converting it in the liver before it enters the bloodstream as fuel.
Your gut uses two separate absorption pathways: one for glucose, one for fructose. Each pathway has a ceiling. If you only eat glucose (like most standard gels), you absorb about 60 grams per hour before the pathway saturates. Add fructose and you open a second lane. Mix the two and you can push toward 90 grams per hour. Most products formulated for high-carb intake use a 2:1 glucose-to-fructose ratio. Check the label before race day.
Front-load the early miles
A 2024 study that tracked 100-mile runners found the gap between faster and slower finishers was biggest in the first half of the race, not the second.5 Faster runners ate more carbs early and kept their blood sugar stable throughout. Slower runners fell behind in the first half and never recovered. The instinct to wait until you feel like eating is the exact wrong strategy.
How high can you go?
The 60 to 90 grams per hour recommendation is the current standard. But newer research suggests that gut-trained athletes may benefit from going higher. A study found that athletes consuming 120 grams per hour during a mountain marathon had significantly more leg strength and better running fitness 24 hours after the race than those taking in 60 or 90 grams per hour.6 The key: those athletes spent four weeks training their gut to handle the higher intake before race day. You cannot show up and eat 120 grams per hour cold.
A Simple Race-Day Fueling Plan
You do not need a spreadsheet. You need a rhythm.
- First 30 minutes: Eat something. Even if you feel fine. One gel, half a banana, a few chews.
- Every 20–25 minutes after that: Eat again. Set an alarm if you need to.
- At every aid station: Grab food even if you are not hungry. Banana, potato, broth. Keep moving if you can.
- After mile 50 in a 100: Real food becomes more important. Gels get harder to stomach. Rice, potatoes, and broth are easier on a tired gut.
- If you feel nauseous: Don't stop eating immediately. Low blood sugar and low electrolytes are both common causes. Try a gel and an electrolyte tab and give it 10 to 15 minutes.
The right gel matters too. See our gel reviews and carb comparisons to find one that works for your gut before race day.
Practice This in Training, Not on Race Day
Your race-day fueling plan should not be new. Every long run over 90 minutes is a chance to practice. Eat on a schedule. Test different gels and real foods. Find out what your gut tolerates at race effort.
The runners who finish 100-mile races are not tougher than the ones who drop out. They eat more. Start practicing now.
- Costa RJS, Gill SK, Hankey J, Wright A, Marczak S. "Perturbed energy balance and hydration status in ultra-endurance runners during a 24 h ultra-marathon." British Journal of Nutrition. 2014;112(3):428–437. doi:10.1017/S0007114514000907
- Stuempfle KJ, Hoffman MD, Weschler LB, Rogers IR, Hew-Butler T. "Race diet of finishers and non-finishers in a 100 mile (161 km) mountain footrace." Journal of the American College of Nutrition. 2011;30(6):529–535. doi:10.1080/07315724.2011.10719999
- Wardenaar FC, et al. "Real-Time Observations of Food and Fluid Timing During a 120 km Ultramarathon." Frontiers in Nutrition. 2018;5:32. doi:10.3389/fnut.2018.00032
- Tiller NB, Roberts JD, Beasley L, et al. "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. 2019. doi:10.1186/s12970-019-0312-9
- Inamura N, Taniguchi H, Yoshida S, Nishioka M, Ishihara K. "A comparative observational study of carbohydrate intake and continuous blood glucose levels in relation to performance in ultramarathon." Scientific Reports. 2024. doi:10.1038/s41598-023-51048-6
- Urdampilleta A, Arribalzaga S, Viribay A, et al. "Effects of 120 vs. 60 and 90 g/h Carbohydrate Intake during a Trail Marathon on Neuromuscular Function and High Intensity Run Capacity Recovery." Nutrients. 2020;12(7):2094. doi:10.3390/nu12072094
- Noakes TD, Prins PJ, Buga A, D'Agostino DP, Volek JS, Koutnik AP. "Carbohydrate Ingestion on Exercise Metabolism and Physical Performance." Endocrine Reviews. 2026;47(2):191–243. doi:10.1210/endrev/bnaf038
- John GM, Juez A, Armenteros M, et al. "Does Distance Matter? Metabolic and Muscular Challenges of a Non-Stop Ultramarathon with Sub-Analysis Depending on Running Distance." Nutrients. 2025;17(22):3801. doi:10.3390/nu17223801