What To Do When It’s Hard To Fuel

Common causes and solutions for when it’s hard to eat during a race.

Photo: Getty Images

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It is no secret the body needs calories to run efficiently. However, it is a common occurrence for long-distance runners that their stomach shuts down and can reject food, especially in races when power and strength are imperative.

While not every obstacle is controllable, when it comes to fueling, being aware of what can cause digestive issues, how to prevent them—and how to work through a particular issue when it arises—could prevent a DNF.

What Causes Issues in Fueling?


When exercising for an extended period of time—and especially when running in an ultra-distance race—the body starts to divert the blood that usually aids in digestion to the cardiovascular system. The lack of resources going to digestion causes the body to lose appetite or even reject food through vomiting or indigestion.

Pre-Race Jitters

Heightened emotions, whether they are those of excitement or anxiety, can confuse the electrical communication between the digestive tract and the brain, causing gastrointestinal distress. Confusing the body before the race begins can lead to issues in fueling as the day goes on. 

Pallet Fatigue

Pallet fatigue is caused by consuming similar tasting foods or liquids repeatedly for a long period of time, such as energy gels during an ultramarathon. “Early on in my racing career, I experienced issues with fueling, especially in using snacks that were highly processed,” says Kelly Wolf, a professional trail runner from Basalt, Colorado, who also holds a certification in Holistic Nutrition.  “Every race where I would go past 50k, I would experience pallet fatigue. I just could not bring myself to have another gel. Could not eat anymore. Not eating always ended in a bonk.” (Wolf is sponsored by Spring Energy, which is an endurance sports nutrition company that aligns itself with clean eating.)

RELATED: Trail Tested: Spring Energy Gels

Environmental Factors

Running in warmer temperatures or at higher elevations than an athlete trained at can cause the body to work harder, again diverting blood to keep the aerobic system in homeostasis. “Heat causes the body to focus on cooling down, especially through sweat, depleting electrolytes,” explains Jennifer Sommer-Dirks, a Denver-based registered dietician who specializes in endurance sports fueling. “While elevation makes it harder to function and can bring on nausea quicker. The lack of oxygen makes the body work harder.”


It is almost inevitable that a runner will end up in a calorie-deficit during a race; however, fueling with 30-40 percent of what is burned will help the body stay efficient and energized.“Be present to how much you are actually eating,” says Andrew Simmons, a running coach based in Golden, Colorado, who has coached and crewed runners in the 100- and 200-mile distances. “Most athletes under-fuel. Hydration is part of the fueling plan. Without sugar, we do not absorb as much water in the gut.” The sugars necessary for absorption are found as glucose, from broken-down carbohydrates, or fructose, found in fruit.

What You Can Do When Issues Arise

Slow down

The body starts to reject food when it is overextended. Slowing down the pace and allowing the body to take in calories will prevent total decompensation in the race. “Walk, rehydrate, until your body is starting to refind homeostasis,” says Simmons. “It might take a while to get back to normal if conditions are not ideal.”

Use terrain to time fueling

Along with slowing down the pace to increase fueling, learning to time fueling with less demanding terrain will aid in digestion when the body is not cooperating. If a runner fuels on flats or even downhills, when their body is not working as hard, the food is more likely to be digested and used efficiently. Trying to ingest fuel going up steep terrain can be logistically challenging, but there’s an added element of difficulty when your breathing and heart rate increase, too.

RELATED: Your Race Fueling Plan: Evolved

Settle the stomach

When nausea or indigestion hits, there are plenty of resources to help settle the gut before any nutrients are lost. “Sometimes bubbly stuff helps, such as soda or carbonated water,” says Sommer-Dirks. “Ginger chews, which have some carbs, are also beneficial, especially since you just suck on them rather than chew. I also encourage clients to try peppermint or Tums to decrease the rising acid.”

It is also helpful to move to sipping water and minimizing the amount of food that is consumed at one time (while increasing the frequency of taking in calories.) The least amount of stress that is put on digestion, the better. If vomiting occurs, it is important to rehydrate and take in electrolytes.

Liquid Calories

There could be a point in an event where the body is done taking in any solid calories for a while. “You can likely finish a race with liquids alone,” says Sommer-Dirks. Of course that wIll depend on the person and how the body uses fat stores. There is the danger of bonking, especially if the blood sugar gets too low. And the body runs out of glycogen stores.” She says that most people only have enough for two hours of strenuous exercise while fasted. However, since ultrarunning is usually done at a slower effort, the body can go a little longer if needed.

There are many higher-calorie and carb-based liquid options—including drink mixes from Tailwind, Skratch, Maurten and Never Second—that can replace solid food if necessary.

Training your Gut

Build stomach strength like a muscle

“Train your gut in the same way you train your muscles,” says Sommer-Dirks. “Start with the smallest and simplest foods as possible, and give a little bit of time to digest before the run. Gradually start adding new foods and moving the timing closer to the start of the run. You will want to start practicing on slower-paced days, avoiding days when you are doing a key workout.”

RELATED: 5 Gut Training Tips For People With Crappy Guts

Keep your body on a schedule

By practicing consuming meals and more significant portions of food, a runner can keep their already existing nutritional timing and avoid throwing their body into further disarray. 

“When I ran Ultra Trail Cape Town, it was a  warmer day than I was ready for. I had to stop eating, running low on food I could get down, I just did not have enough options,” Wolf says. “I noticed a lot of the other runners were eating real food, like sushi and burgers. I realized if I was going to be out for more than six hours, I was going to need a real meal option.”

Find what works for you

The base phase of training can be a great time to experiment with different foods, timing, and portion size. “Your base phase of training can be one of exploration,” Simmons says. “Take time to understand what you like to eat and what sits well with you.” The decreased time in training can also be a handy time to play around with new food preparation techniques or recipes.

Fueling to Avoid Issues

In the midst of a training cycle, it can be difficult to try something new. By adjusting already existing habits, stomach issues can be prevented.


Water is imperative in the digestion process. Not only does it break down food, but it also keeps plasma thin so that blood can circulate through the body (allowing both muscles and th stomach to get blood.) By keeping the hydration game strong, a runner will be able to remain in homeostasis longer and benefit from fueling. To prevent hyponatrimia, or an overabundance of water flushing out sodium, it is crucial to include an electrolyte mix, salt tablets, or food higher in sodium when paired with diligent hydration.

Be mindful of your fuel

There can be too much of a good thing, and any food in excesses can be tough on the stomach, explains Sommer-Dirks. She recommends spacing out sugars and water and to avoid overuse of fiber and caffeine to avoid stressing the stomach. “Simple carb sources are going to be the best fuel, especially paired with electrolytes,” she adds. “You will not get much from dense fat during a race.” 

RELATED: There’s Lots Of Fueling Options Out There. Here’s What You Should Know.

Get Real

Many trail runners have found success in switching to real foods for as much of the race as possible. “I eat primarily real food in a race, such as rice, oats, fruit, and nuts,” Wolf says. “I avoid over-processing when I can. Faster and higher-hitting gels still have their place, but the majority is real. That way, I can have variety in flavor. Real food can take you much further and is way cheaper.”

An upset stomach, or inability to eat, can throw the body off of its game and cause major issues, such as an increased heart rate, dehydration, or extreme fatigue. By finding solutions to deal with digestion distress or learning to prevent future issues, an athlete can keep their body running strong.

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