Most Ultra Runners Don't Eat Enough. Here's How Much You Actually Need.

Here is a number that should bother you: in one study of 25 runners in a 24-hour race, the average was just 37 grams of carbs per hour.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 For most runners, the recommended target is 60 to 90 grams per hour. Most runners are not even close.

Other studies find the same gap. Many runners think they eat enough during a race, but they don't.

Why Fueling Strategy Makes or Breaks Your Ultra

Your body stores only a few hours of carbs in your muscles and liver. When those run low and you are not eating, your blood sugar drops. You slow down, your thinking gets cloudy, and your gut starts to rebel.

A small study at the Western States 100 followed 16 runners. The 6 who finished ate almost twice as many carbs per hour, for their body size, as the runners who dropped. The biggest gap came in the first 30 miles. The authors said food was not the only reason, but it clearly mattered.²

In longer races, the gap is even bigger. A 2025 study estimated 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 No one can fully match what they burn during a race. But you can close the gap.

A 2024 study put glucose monitors on 22 runners in a 100-mile trail race. Faster finishers ate more carbs for their body size. Their blood sugar was also steadier. Slower finishers had blood sugar swings about 14 mg/dL wider. Runners whose blood sugar swung more tended to run slower.⁵

Here is why that matters. The fatigue you feel late in a race is not just your legs giving out. One idea is that your brain watches your blood sugar. When it starts to drop, your brain tells you to slow down, even if your muscles still have fuel left. A 2026 review of more than 160 studies argues that the main reason eating helps is that it stops blood sugar from dropping. Not everyone agrees, but it fits what runners feel late in a race.⁷

Why Do So Many Ultramarathon Runners Under-Fuel?

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. A study of 272 runners at Western States found that 96 percent had stomach problems. Among finishers, 44 percent said it hurt their race. Among runners who dropped, 36 percent said it was part of why they quit.¹⁴ 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.

How Many Calories Do You Need Per Hour During an Ultra?

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 deep into a long race, your pace is slower and you need less. The ISSN suggests 30 to 50 grams per hour for ultras.⁴ Many runners still aim for about 60 if their gut allows it.

Athletes who have put in several seasons of gut training can push beyond 90 grams. The key is using a 2:1 glucose-to-fructose product. Glucose and fructose use different absorption pathways, so combining them raises the ceiling on how much your gut can process per hour. Research suggests some trained athletes can reach 90 to 120 grams per hour with this approach. That is not a starting point. Start at 60 grams, build from there, and only push past 90 grams if you have trained at 75 to 90 grams consistently without distress.

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 of 100-mile runners found faster finishers ate more carbs than slower ones, mostly in the first half of the race.⁵ Their blood sugar also stayed steadier. Waiting until you feel like eating is the wrong plan.

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 of 26 elite trail runners found that those who ate 120 grams per hour during a mountain marathon lost less leg strength and running fitness over the next 24 hours than those eating 60 or 90 grams.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.

What the research says: A 2026 review in the Journal of Nutrition says some endurance athletes, like pro cyclists, now try 120 to 200 grams of carbs per hour. The authors say no study yet shows those amounts help. They suggest the upper limit for trained athletes may rise from 90 to 120 grams per hour.¹³ A 2026 review by Plews and colleagues in Sports Medicine looked at whether more than 90 grams per hour helps. It found the proof is still thin.¹¹ A 2022 study had 11 trained cyclists ride for three hours. At 120 grams per hour, their bodies burned a bit more carb from food than at 90 grams. But they used a smaller share of what they ate: about 76 percent, down from 86 percent. Their stomachs felt about the same at both levels.¹² The ISSN position stand on ultra nutrition suggests 30 to 50 grams of carbs per hour for ultra runners. It says 90 grams per hour may not be realistic in races over six hours.⁴

What this means for you: More carbs per hour helps, up to a point. For most runners, 60 to 90 grams per hour assumes you are moving at a decent clip. On hiking sections, overnight miles, and the last quarter of a 100, we think the ISSN's 30 to 50 grams per hour is a more realistic target.⁴ Going past 90 grams per hour has not been shown to help runners. Your body burns a little more, but it uses a smaller share of what you eat, and most of the research so far is on cyclists. If you want to try it, train your gut first.

There is also a ceiling that sits above all of this. A 2025 study in Current Biology tracked 14 elite ultra athletes in races from 24 hours to 13 days. During some races, athletes burned six to seven times their resting rate, or about 7,000 to 8,000 calories a day. But over 30 to 52 weeks of training, their average fell to just under 2.5 times resting rate. Only a few athletes went over it, and not by much. The body can burn a lot for a short time, but it cannot keep that pace for months.⁹

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. Late in a race, your blood sugar can swing and spike even when you eat on schedule. One review suggests muscle damage and inflammation may make it harder for your muscles to use sugar. The proof is still limited.¹⁰ This is not a sign to stop eating.
• 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.

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.

Finishers tend to eat more than the runners who drop. Start practicing now.