What Is Gut Training

If you’re an endurance athlete, you’ve probably heard (or said) things like “My stomach is so sensitive” or “I couldn’t keep anything down during that session.” What many athletes don’t realise is that the gut is trainable just like your legs, lungs, or cardiovascular system.

Your gastrointestinal tract plays a critical role in delivering carbohydrates and fluids during prolonged exercise, which means it can be a major factor in your overall performance. In fact, research shows that the gut can adapt over time to tolerate and process more fuel during activity.

Gastric emptying, how quickly food and fluids leave your stomach and become usable energy, is a key process here. Believe it or not, the stomach can adapt to handling larger volumes. Just look at competitive eaters: through training, they’re able to tolerate enormous amounts of food with surprisingly little discomfort. While endurance athletes don’t need to go to such extremes, this example demonstrates the gut’s incredible capacity to adapt.

Training your gut improves two main things:

  1. Stomach expansion – allowing it to comfortably hold more fuel.

  2. Tolerance – reducing the feeling of fullness or discomfort when your stomach is working hard.

How Digestion Affects Performance

Digestion directly influences both physical output and mental focus.

When digestion is efficient:

  • Nutrients are absorbed properly

  • Blood sugar stays stable

  • You have steady energy and clearer concentration

But when digestion struggles whether due to poor fueling timing, heavy foods, or gut sensitivity your body diverts blood to the digestive system instead of the working muscles or brain. This can lead to:

  • Sluggishness

  • Cramps

  • Nausea

  • Dips in energy

  • Early fatigue

  • Brain fog

Good digestion supports consistent energy and endurance. Poor digestion can sabotage even your best-planned training session.

The Science Behind Gut Training

When we consume carbohydrates during exercise, the body relies on specific transporters to move and absorb them. Understanding these helps explain why we need to train our guts.

There are two key carbohydrate transporters:

1. SGLT-1 (Sodium-Dependent Glucose Transporter)

This transporter absorbs glucose, but it depends on sodium to work. Think of sodium as the “helper” molecule. When sodium enters the cell, glucose gets pulled in right alongside it. Without enough sodium, glucose absorption slows, which can contribute to GI discomfort and poor fueling.

2. GLUT-5

GLUT-5 absorbs fructose, and the key difference is that it does not rely on sodium. This is why many sports nutrition products use a glucose-to-fructose ratio; it takes advantage of both transporters to increase total carbohydrate absorption and reduce the risk of gut distress.

Of course, each transporter has a limit. When we exceed the maximum absorption rate of glucose alone, symptoms like bloating, cramps, or nausea appear. Combining different types of carbs allows athletes to absorb more fuel without overwhelming one system.

Why Bother Training Your Gut?

In short: to improve comfort, consistency, and performance.

Regular gut training teaches your stomach and intestines to:

  • Absorb carbohydrates and fluids more efficiently

  • Tolerate higher fueling rates without discomfort

  • Reduce risks of nausea, cramps, bloating, or diarrhoea

  • Sustain higher energy output during long or intense sessions

This ultimately delays fatigue and boosts endurance, especially in races lasting 90+ minutes.

How to Start Gut Training

Before you begin, it’s important to know your ideal carbohydrate target for training and racing. Once you have your target, here’s how to build your plan:

1. Start Early – 6 to 8 Weeks Before Race Day

This allows enough time for your stomach and intestines to adapt gradually.

2. Begin With a Comfortable Fueling Level

This may be 30 g/h for some, or 60 g/h for others.
Each week, increase your intake slightly so you can reach your race-day target before your taper. You could start by using a GEL30 and then increasing to a GEL50. 

3. Practice With Race-Day Fuel

Use the same:

  • Products

  • Timing

  • Textures

  • Drinks

This trains both your gut and your confidence. During training, sip fluids frequently rather than all at once, and try fueling before harder workouts to simulate race conditions. Keeping a fueling log can help you identify what works best.

So… What Happens Once Your Gut Is Trained?

Once your gut is adapted to absorb higher amounts of carbohydrates comfortably, you’re ready to race and train on a high-carb fueling strategy which means more energy, better endurance, and reduced risk of GI issues on race day.

Your gut becomes an asset rather than an obstacle.