Exercise-Induced Nausea: Why It Happens and How to Stop It

Why Do Athletes Get Nauseous During Exercise? The Science Behind Exercise-Induced Nausea

If you've ever felt your stomach turn halfway through a hard run, wanted to throw up after a brutal interval workout, or struggled to eat during an ultramarathon, you're not alone.

Exercise-induced nausea is surprisingly common. In fact, studies report that anywhere from 30–90% of endurance athletes experience gastrointestinal (GI) symptoms during training or competition, with nausea ranking among the most common complaints. It's especially prevalent in marathon runners, ultrarunners, triathletes, cyclists, and CrossFit athletes. Research also suggests that nausea becomes more common as exercise duration and intensity increase.

The good news?

Exercise-induced nausea is usually preventable.

Understanding why it happens is the first step toward keeping your stomach happy so you can focus on performing your best.

Let's dive into the science.

What Causes Exercise-Induced Nausea?

There's rarely one single cause.

Instead, nausea usually results from several factors working together.

The review identified multiple contributors, including:

• Reduced blood flow to the digestive system

• High exercise intensity

• Heat stress

• Dehydration

• Overhydration

• Improper nutrition

• Certain medications

• Anxiety

• Underlying medical conditions

Let's look at each one.

1. Reduced Blood Flow to Your Gut (The Biggest Culprit)

When you exercise, your body has to prioritize where blood goes.

Instead of sending blood to your stomach and intestines, it redirects much of it toward your working muscles, heart, lungs, and skin.

Research has shown that blood flow to the gastrointestinal tract can decrease by up to 80% during intense exercise.

While this helps support exercise performance, it comes at a cost.

Reduced blood flow means:

• Slower digestion

• Delayed stomach emptying

• Reduced nutrient absorption

• Irritation of the intestinal lining

The longer and harder you exercise, the more pronounced these effects become.

This is one reason nausea is so common during marathons and ultramarathons.

2. High Exercise Intensity

Intensity matters.

The harder you exercise, the greater the physiological stress placed on your digestive system.

High-intensity efforts produce:

• Greater sympathetic ("fight or flight") activation

• More redistribution of blood away from the gut

• Increased stress hormone release

• Greater accumulation of metabolites

Research consistently shows GI symptoms become more common as exercise intensity increases.

This explains why many athletes feel fine during easy Zone 2 runs but become nauseous during:

• VO₂ max intervals

• Hill repeats

• Sprint finishes

• CrossFit workouts

• Hard cycling efforts

3. Heat Stress

Hot weather dramatically increases nausea risk.

When exercising in the heat, your body diverts even more blood toward the skin to help cool itself.

That means even less blood is available for digestion.

Heat stress can also increase:

• Dehydration

• Core body temperature

• Gut permeability

• Overall physiological stress

These changes make nausea far more likely during summer races and long workouts in hot environments.

4. Dehydration

Even mild dehydration can make nausea worse.

As fluid losses increase:

• Blood volume decreases

• Heart rate rises

• Blood flow to the gut falls even further

• Stomach emptying slows

The combination creates the perfect environment for stomach discomfort.

This is why athletes who fall behind on fluids often report nausea late in races.

5. Drinking Too Much Water

Believe it or not...

You can also drink too much.

Excessive water intake may contribute to exercise-associated hyponatremia—a dangerous condition where blood sodium levels become abnormally low.

Early symptoms often include:

• Nausea

• Vomiting

• Headache

• Confusion

• Swelling

While relatively uncommon, hyponatremia is most often seen during long endurance events where athletes consume large amounts of plain water without replacing sodium.

The goal isn't simply to drink more.

It's to drink appropriately.

6. Eating the Wrong Foods Before Exercise

Nutrition mistakes are among the easiest causes of nausea to fix.

Foods that commonly trigger GI distress include:

• High-fat meals

• High-fiber foods

• Large meals

• Spicy foods

• Excess protein immediately before exercise

These foods empty from the stomach more slowly, increasing the likelihood they'll still be sitting there once exercise begins.

For most athletes, finishing a large cheeseburger an hour before a long run isn't the best strategy.

7. Carbohydrates Can Help…or Hurt

Carbohydrates are essential for endurance performance.

But consuming the wrong type, or the wrong concentration, can backfire.

Highly concentrated carbohydrate drinks slow gastric emptying and may increase GI distress.

Research generally supports sports drinks containing approximately 6–8% carbohydrate concentration, which balance energy delivery with stomach comfort.

Athletes should also practice their race nutrition during training rather than experimenting on race day.

8. NSAID Use

Many athletes routinely take anti-inflammatory medications such as ibuprofen before races.

Unfortunately, this can increase GI problems.

NSAIDs may:

• Reduce blood flow to the gut

• Increase intestinal permeability

• Increase the risk of GI bleeding

• Worsen nausea

The review recommends avoiding unnecessary NSAID use before endurance events whenever possible.

9. Anxiety and Pre-Race Nerves

Have you ever felt nauseous before the starting gun?

You're not imagining it.

Stress and anxiety activate the sympathetic nervous system, which slows digestion and alters communication between the brain and gastrointestinal tract.

Research has linked higher anxiety levels with greater gastrointestinal symptoms in endurance athletes.

This is one reason experienced racers often have fewer stomach problems; they've learned how to manage pre-race stress.

10. Motion Sickness

Certain sports naturally increase motion-related nausea.

Examples include:

• Open-water swimming

• Trail running

• Mountain biking

• Rowing

• Sailing

Constant changes in body position can create sensory conflicts that trigger nausea in susceptible athletes.

When Nausea May Be a Medical Emergency

While most exercise-induced nausea is harmless, sometimes it can signal something more serious.

Seek immediate medical attention if nausea occurs alongside:

• Chest pain

• Severe abdominal pain

• Confusion

• Loss of consciousness

• Persistent vomiting

• Bloody vomit

• Bloody stool

• Severe headache

• Signs of heat stroke

These symptoms require prompt evaluation.

How to Prevent Exercise-Induced Nausea

Fortunately, most athletes can dramatically reduce nausea by making a few simple changes.

Practice Your Race Nutrition

Never try new foods or sports drinks on race day.

Train your gut just like you train your legs.

Stay Hydrated—But Don't Overdo It

Drink according to your sweat rate.

Replace sodium during longer events.

Avoid excessive plain water intake.

Avoid Large Meals Before Exercise

Most athletes tolerate meals best when eaten 2–4 hours before exercise.

Smaller carbohydrate-rich snacks often work well within an hour.

Build Heat Tolerance

Gradually acclimating to hot environments can reduce heat stress and improve GI comfort.

Pace Yourself

Starting too fast dramatically increases nausea risk.

Conservative pacing early often leads to better performance later.

Reduce Pre-Race Stress

Deep breathing, visualization, and sticking to a familiar pre-race routine can reduce anxiety-related nausea.

The Bottom Line

Exercise-induced nausea is common but it isn't something athletes simply have to accept.

The scientific evidence suggests it's usually caused by a combination of reduced blood flow to the digestive system, exercise intensity, dehydration, heat stress, nutrition choices, anxiety, and environmental factors.

Fortunately, many of these risk factors are controllable.

By practicing race nutrition, staying appropriately hydrated, pacing intelligently, avoiding unnecessary NSAID use, and preparing for environmental conditions, most athletes can dramatically reduce the chances of nausea interfering with their performance.

If nausea occurs repeatedly despite good preparation, or is accompanied by concerning symptoms, it's worth discussing with a healthcare professional to rule out an underlying medical condition.

Your stomach doesn't have to be the weakest link in your next race.

References

1. Costa RJS, et al. Exercise-Induced Gastrointestinal Syndrome: Implications for Health and Performance. Sports Medicine. 2017.

2. de Oliveira EP, Burini RC. The impact of physical exercise on the gastrointestinal tract. Current Opinion in Clinical Nutrition & Metabolic Care. 2009.

3. ter Steege RWF, Kolkman JJ. Review article: the pathophysiology and management of gastrointestinal symptoms during physical exercise. Alimentary Pharmacology & Therapeutics. 2012.

4. Wilson PB. Gastrointestinal symptoms in runners: prevalence, risk factors and management. Sports. 2019.

5. Hoffman MD, et al. Medical services at ultra-endurance foot races in remote environments: medical issues and consensus guidelines. Sports Medicine. 2014.