How to Train Your Stomach to Eat While Running

October 18, 2025 •

4 min read

Up to 90% of distance runners experience some form of gastrointestinal (GI) distress during training or a race. The key to preventing nausea, cramping, and bloating is to learn how to train your stomach to eat while running, a process known as gut training.

Quick Summary

Gut training teaches your digestive system to handle fuel during exercise by gradually increasing carbohydrate and fluid intake. It reduces GI distress, improves nutrient absorption, and builds tolerance for high-intensity fueling, ensuring a steady energy supply without discomfort.

Key Points

Start Early and Gradually: Introduce new foods and higher carbohydrate loads slowly over several weeks during training runs to build tolerance, avoiding sudden changes on race day.
Prioritize Fluids: Integrate water and electrolyte-rich sports drinks into your intake routine, as proper hydration is essential for digesting carbs and preventing GI distress.
Choose Low-Fiber Fuel: Opt for easily digestible, low-fiber carbohydrates like gels, chews, or refined real foods (bananas, white rice) during high-intensity efforts to prevent stomach upset.
Practice Race-Day Fueling: Use your long training runs to simulate your race-day nutrition plan, including the specific products and intake timing you intend to use.
Listen to Your Body: Pay close attention to how your gut responds to different foods and volumes. Some discomfort is normal during training, but if symptoms worsen, scale back and re-evaluate your approach.
Time Your Meals: Plan your pre-run meals several hours in advance, avoiding large meals or high-fat/high-fiber foods immediately before a run.
Fuel Consistently: Aim for regular, small intakes of fuel every 30-45 minutes on longer runs to maintain steady energy levels and avoid overwhelming your digestive system.

Understanding the Science of Gut Training

When you run, your body prioritizes sending blood flow to your working muscles, lungs, and heart, diverting it away from your gastrointestinal (GI) tract. This reduced blood flow can impair digestion, leading to common issues like nausea, bloating, cramps, and diarrhea, collectively known as "runner's stomach". The good news is that your gut is a highly adaptable organ, much like your leg muscles, and can be conditioned to tolerate the stress of eating during exercise.

Gut training involves systematically exposing your digestive system to fluids and carbohydrates during workouts. This repeated exposure leads to physiological adaptations, including faster gastric emptying and improved nutrient absorption efficiency. By practicing your fueling strategy in training, your body learns to digest food more effectively even with limited blood flow, reducing the risk of a race-ruining GI meltdown. Research indicates that significant improvements can be seen in as little as two weeks, with optimal tolerance achieved over several months.

The Gradual Process of Training Your Gut

Training your gut is a progressive process that requires patience. The golden rule is simple: start small and build up gradually, never trying anything new on race day. Your training runs, especially your long efforts, are the perfect opportunity to experiment and find what works for your body.

Implement a step-by-step fueling protocol

Start with fluids: For runs over 60 minutes, begin by introducing small, regular sips of water. Once comfortable, add a low-concentration sports drink (around 4–8% carbs) to get your body used to processing sugars while moving.
Add low-carb fuel: After your gut has adapted to sports drinks, incorporate small portions of easily digestible carbs like a half gel or a few energy chews every 30–45 minutes during your runs. Always consume with water to aid absorption.
Increase intake gradually: Over several weeks, slowly increase the carbohydrate load per hour during your long runs, aiming for 30–60 grams per hour for moderate-length runs (1–2 hours) and 60–90 grams per hour for efforts lasting longer than 2 hours. Use a food journal to track intake and note any symptoms.
Simulate race conditions: As your goal event approaches (6–10 weeks out), practice your exact race-day nutrition plan during your longest training runs. Test the specific products, timing, and hydration amounts to eliminate surprises.

Choosing the Right Fuel: Gels vs. Real Food

For endurance fueling, there are two primary categories of options: engineered sports nutrition products (gels, chews, drinks) and real, whole foods. The right choice depends on personal preference, intensity, and digestion.


Feature	Engineered Sports Nutrition (Gels, Chews)	Real Foods (Dates, Bananas, Potatoes)
Absorption Speed	Designed for very rapid absorption into the bloodstream for quick energy.	Generally absorbed slower, providing steadier energy.
Convenience	Highly portable, pre-portioned, and easy to consume on the move.	Requires carrying and potentially preparing beforehand; can be more cumbersome.
Digestion	Formulated with simple carbs to minimize GI distress, especially in gels combining glucose and fructose.	Can contain fiber, fat, and protein which slow digestion and can cause issues for some.
Flavor	Often limited to very sweet, artificial flavors that can cause "flavor fatigue".	Offers a wider variety of natural, savory, and sweet flavors to prevent taste burnout.
Nutritional Value	Provides concentrated carbohydrates and electrolytes, but fewer micronutrients.	Contains beneficial fiber, vitamins, and minerals that can contribute to overall health.

For higher-intensity efforts where chewing is difficult, gels and drinks are often the most practical choice. In longer, lower-intensity events, real foods can provide a welcome change of pace and more sustained energy. Many athletes find success by incorporating a mix of both.

Avoiding Common GI Irritants

Even with proper gut training, certain foods can trigger discomfort. For 1-3 days leading up to a race or a long training run, it is wise to reduce your intake of foods that are difficult to digest.

High-Fiber Foods: Items like beans, broccoli, and whole grains slow digestion. Opt for refined grains like white pasta or rice instead.
High-Fat and High-Protein Foods: These macronutrients also take longer to digest and should be limited before and during runs.
Caffeine: While a performance booster for some, it can be a gut irritant and stimulate bowel movements in sensitive individuals.
NSAIDs: Non-steroidal anti-inflammatory drugs like ibuprofen can aggravate the GI tract and increase permeability, potentially leading to issues.
Artificial Sweeteners and Sugar Alcohols: These are known culprits for causing digestive upset.

The Crucial Role of Hydration

Proper hydration is inextricably linked to successful fueling. Without adequate fluid, concentrated carbohydrates from gels or chews can draw water into the intestines, causing cramps and diarrhea. Staying well-hydrated throughout the day and during your run is critical.

Pre-run Hydration: Drink fluids consistently throughout the day, aiming for a pale, straw-colored urine. Consume 17-20 ounces of water or a sports drink 2-3 hours before a long run.
During the Run: Aim for 4-8 ounces of fluid every 15-20 minutes. On runs over an hour, include an electrolyte-rich beverage, especially if you are a salty or heavy sweater. You can train your stomach to tolerate more fluid over time.
After the Run: Replenish fluids and electrolytes by drinking 16-24 ounces for every pound lost during your run.

Conclusion

Training your stomach to eat while running is a strategic process that is as vital as physical training for endurance athletes. By starting with a gradual progression of low-intensity food and fluid intake, you can condition your GI tract to effectively handle more carbohydrates and liquid. Experimenting with different fuel sources, avoiding known irritants, and prioritizing hydration are all fundamental components. With a little practice and patience, you can turn your stomach from a potential liability into a performance-enhancing asset, allowing you to run stronger and avoid the distress that can derail your goals. The adaptability of your gut means that with consistent practice, you will build the digestive tolerance needed to confidently fuel your next race or long run. For more evidence-based recommendations, consult research from the National Institutes of Health.

Frequently Asked Questions

Gut training is the process of teaching your digestive system to tolerate and absorb nutrients more efficiently during exercise. By consistently consuming food and fluids during training runs, you increase your body's capacity to deliver energy to your muscles without causing gastrointestinal distress.

Begin by incorporating small amounts of easy-to-digest carbohydrates and fluids on your longest training runs. Over several weeks, gradually increase the volume and concentration of your fuel, monitoring your body's response and adjusting as needed.

For fueling during runs, focus on simple carbohydrates like sports gels, chews, and certain easily digestible real foods (e.g., bananas, dates). These sources provide quick energy and are less likely to cause stomach upset compared to high-fiber or complex carbs.

A common starting point is 30–60 grams of carbohydrates per hour for runs lasting over 90 minutes. More advanced athletes may build tolerance up to 90 grams per hour or more, often using dual-source carbs (glucose and fructose) for better absorption.

Yes, many runners use real food like bananas, dates, or boiled potatoes. Real food can be just as effective and sometimes gentler on the stomach, but it may be less convenient and can vary in nutrient content. Always test real food options during training, not on race day.

Proper hydration is crucial. Consuming fluids helps your body absorb carbohydrates and move food through the digestive system efficiently. Without enough water, concentrated fuel sources like gels can draw fluid into the gut, causing cramping and dehydration.

Preventing GI distress involves proper gut training, avoiding high-fiber, high-fat, and high-protein meals right before a run, and staying consistently hydrated. It also helps to minimize race-day anxiety and practice your fueling strategy in varying conditions.