Lifestyle

Training Your Gut: The Missing Piece of Endurance Performance

If you’ve ever stressed about what to eat before a long run because you were worried about how your stomach would feel, avoided fueling during a race because your stomach is too “sensitive,” or found yourself sprinting to the bathroom mid-run, just know that you’re not alone.

Gastrointestinal (GI) distress in endurance athletes is actually quite common, affecting 30–90% of endurance athletes,1 depending on the event and conditions.

Why is GI distress so common?

During exercise, especially runs lasting longer than an hour, your body prioritizes sending blood to your working muscles and skin to support movement and regulate temperature.

With blood being sent to working muscles, this means that blood flow to the digestive tract decreases and digestion slows. Food and fluids may sit in the stomach for longer. Additionally, the intestinal lining may become more vulnerable to irritation.1

Combine this with dehydration, heat, jostling from running, nerves before competition, or consuming unfamiliar foods, and GI symptoms become much more likely.

Common GI symptoms include:

Bloating
Side stitches
Nausea
Reflux
Cramping
Diarrhea
Urgent bowel movements

Why You Shouldn’t Avoid Fuel

Many runners respond to GI distress by eating less or not eating at all. While this may seem logical, it often backfires….

Underfueling can lead to:

Early fatigue
Reduced glycogen stores
Poor recovery
Increased perceived effort
Lower training quality
Greater risk of “hitting the wall”

Instead of avoiding food, the goal is to teach your digestive system to handle it.

The good news? Your gut is trainable.

Similar to how you train your muscles, heart, and lungs to keep up with the demands of running, you can train your digestive system to utilize fuel more efficiently and tolerate eating before and during training.

What Is “Gut Training”?

Gut training is the process of implementing and practicing your race-day fueling strategy during training so your digestive system can adapt.

These adaptations can include:2–5

Faster stomach emptying
Improved carbohydrate absorption
Better fluid absorption
Reduced feelings of fullness or bloating
Less nausea, cramping, and urgency during exercise
Greater confidence eating before and during long workouts

In essence, the gut becomes more efficient at delivering the fuel your muscles need.

How Gut Training Works

Think of gut training like progressive overload in strength training. You don’t start by picking up the absolute heaviest weight that you can, you increase the weight gradually over time.

The same applies to fueling and nutrition.

Step 1: Practice Your Pre-Run Meal

If you don’t already, start eating before key workouts rather than only on race day.

Experiment with:

Timing (1–4 hours before)
Portion size
Carbohydrate sources
Fat and fiber content

Many runners tolerate foods such as:

Toast with jam
Oatmeal
Bagel with peanut butter
Banana
Yogurt with cereal

The goal is to discover what works for your body, not what works for someone else. Carbohydrates are the body’s preferred fuel source, are more quickly digested, and thus are preferred before a run.1 Eating a snack or meal too high in fat beforehand may be more likely to cause stomach upset.

Step 2: Practice Fueling During Long Runs

For runs lasting longer than 60–90 minutes, begin practicing carbohydrate intake during training.

Current sports nutrition recommendations generally suggest:6,7

30–60 grams of carbohydrate per hour for exercise lasting 1–2.5 hours.
60–90 grams per hour for longer endurance events, especially when using multiple carbohydrate sources (such as glucose plus fructose).

This isn’t something to jump into overnight.

Instead:

Start with smaller amounts.
Increase gradually over several weeks.
Use the same products you plan to use on race day.

Your gut adapts through repeated exposure.

Step 3: Train Hydration Too

Fluids are also part of gut training.4

Practice:

Drinking while moving
Different bottle or hydration pack systems
Electrolyte beverages
Drinking at race pace

Taking in fluids only when thirsty during training may leave you unprepared for race-day demands.

Foods That May Need More Practice

Some foods are naturally slower to digest and may increase symptoms if eaten too close to exercise.

These include:

High-fat meals
Large portions
High-fiber foods
Spicy foods
Alcohol
Large amounts of dairy (for those who are lactose intolerant)

This doesn’t mean these foods are “bad.” It simply means timing matters.

The Gut-Brain Connection

Your stomach doesn’t function independently from your brain. Pre-race anxiety can amplify GI symptoms through the gut-brain axis.

Stress hormones can alter:

Gastric emptying
Intestinal movement
Sensitivity to normal digestive sensations

This is why practicing your fueling strategy during training is valuable for more than physiology, it also builds confidence. The more familiar eating during exercise becomes, the less stressful race day often feels.

Treat your nutrition plan as part of your workout, not an afterthought.

When GI Symptoms Persist

Occasional stomach discomfort is common.

However, persistent symptoms deserve further evaluation.

If you regularly experience:

Severe abdominal pain
Vomiting
Blood in the stool
Recurrent diarrhea
Significant weight loss
Inability to tolerate fueling

It is worth discussing these symptoms with a sports dietitian and your healthcare provider. Conditions such as food intolerances, irritable bowel syndrome (IBS), celiac disease, inflammatory bowel disease, or other gastrointestinal disorders require individualized management.

Key Takeaways

Training your gut is one of the most overlooked aspects of endurance performance.

Remember:

Your gut is adaptable.
Don’t try new fueling strategies on race day.
Practice eating and drinking during training.
Increase carbohydrate intake gradually.
Hydration deserves practice too.
Consistency, not perfection, is what builds tolerance.

The strongest runners aren’t just training their legs, they’re training their digestive system to support the miles ahead.

Bottom line: A well-trained gut can be the difference between simply finishing a race and performing at your best. By practicing your fueling strategy throughout your training cycle, you’re preparing your entire body to meet the demands of race day.

Connect with our team of dietitians to lock in your fueling and hydration plan.

If you are a teen athlete, check out Sports Plan Pro and all of their resources on fueling, including Gametime Fuel Calculator that covers what to eat before, during, and after games, as well as hydration timing.

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