In endurance sports, nutrition matters just as much as physical training. The longer and harder the effort, the more your body needs a steady supply of energy to keep going. But fueling during exercise isn’t always easy: stomach cramps, nausea, and digestive distress are some of the top reasons athletes drop out of races.

What is Gut Training?

Gut training is exactly what it sounds like: training your digestive system to handle nutrition during exercise, just like you train your muscles. The goal is to gradually teach your gut to absorb and use nutrients efficiently, even under physical stress, helping you avoid stomach issues and stay focused on your effort.

This guide breaks down the science and practical steps to help you adopt this often-overlooked method that can make all the difference on race day.

Understanding digestion during exercise and why Gut Training matters

Why is digestion harder during a race?

During physical effort, your body prioritizes your muscles and lungs by sending them more oxygen and nutrients first. To do this, it reduces blood flow to the digestive system, making it harder to absorb food.

This especially affects gastric emptying, which is the process of moving food from the stomach to the small intestine. This step is crucial because it’s in the intestine that nutrients are absorbed. If gastric emptying is too slow, it can cause heaviness and nausea. If it’s too fast, it can lead to bloating and diarrhea, since the nutrients aren't properly absorbed.

The repetitive movements of running, especially the impact of each step, make things worse by shaking up the contents of the stomach. Without proper preparation, trying to take in carbs or fluids during a race can become a real challenge for your body.

How does gut training improve performance?

By training your digestive system to handle nutrients during exercise, gut training helps reduce digestive issues linked to physical activity, such as cramps, nausea, or bloating. It also improves your ability to tolerate food while running or racing.

Gut training can also help reduce problems with carbohydrate malabsorption, which are often the cause of gastrointestinal discomfort. The result is better absorption of energy, protein, and electrolytes, more effective nutrition during exercise, and a steadier performance with less risk of digestion-related setbacks.

What nutrients should you train with?

As you’ve seen, gut training isn’t just about carbs. For a complete nutrition strategy, it’s important to gradually train your digestive system to absorb three key elements.

• Carbohydrates are your main fuel during exercise. Regular training improves how your body absorbs them and helps reduce digestive issues.

• Electrolytes like sodium, potassium, and other minerals play a key role in hydration and cramp prevention.

• Proteins are essential for recovery and help reduce muscle breakdown during long efforts.

The goal is to gradually teach your gut to tolerate all three during a race. With the right nutrition, like Näak Ultra Energy™ products that combine carbs, protein, and electrolytes in one convenient format, you can make gut training easier and improve nutrient absorption step by step.

How long does it take to adapt?

On average, it takes 6 to 8 weeks to see a noticeable adaptation, and up to 3 to 4 months to reach optimal tolerance. Just like your legs can’t handle an ultra-trail overnight, your gut needs progressive training. The more carbs you want to take in, the more structured your gut training needs to be.

Think of gut training as a long-term investment for a smoother race-day performance.

Gut Training: a Step-by-Step guide

Gut training follows a logical progression that helps your body gradually get used to absorbing nutrients during exercise. Here’s a detailed guide to help you effectively include this approach in your training plan.

Step 1: Set your nutrition strategy

Before you can start training your gut, you first need to know how many grams of carbohydrates you should aim for per hour of racing. This optimal intake depends on your physiology, as well as the duration and intensity of your effort.

To find the right target, use the Näak Nutrition Calculator to generate a personalized nutrition plan based on your profile, race specifics, and performance goals. The goal? To give you clear recommendations to help you optimize your nutrition.

Step 2: Gradually increase your intake

Like strength training, gut training is all about progression. Start with a small, manageable amount of fuel during your workouts, then slowly increase it each week until you hit your target intake.

This gives your digestive system time to adapt and helps avoid discomfort. Experiment with timing and quantity, and tune in to how your body responds.

Step 3: Test different fuel types

Finding the right nutrition strategy isn’t just about how much energy you take in. It’s also about identifying the formats that work best for you. Some prefer bars, others go for a drink mix, while some athletes swear by gels.

Training is the perfect time to try out these options and see what suits you in terms of taste, texture, and tolerance. After each session, take notes to figure out what works best and avoid mistakes on race day.

Once you’ve made your selection, practice with those products to get your digestive system used to processing them efficiently. Also think about adapting your choices to the terrain.Drink mixes and gels are easier to consume while running, while bars and waffles are ideal during lower-intensity workout.

Näak tip: On climbs, take advantage of the slower pace to eat solid foods like bars or waffles. On flatter sections, go for liquid or semi-liquid fuels that are easier to digest while in motion.

Step 4: Practice fueling while running

Eating while running isn’t something that comes naturally, but it’s a skill you can develop by adding one or two gut training sessions per week.

These sessions help you get used to taking in nutrients during exercise, especially during long runs or more intense workouts.

Näak tip: To get the most out of your training, try running right after a meal to train your gut to handle digestion while moving.

Over time, this approach helps reduce the risk of discomfort and improves your digestive tolerance.

Step 5: Test your plan in real conditions

To be fully ready, you need to simulate race conditions. Same pace, same terrain, same nutrition plan. The more your body is used to the real thing, the smoother race day will be.

Study the course

Studying the course is an important part of your preparation and allows you to anticipate key moments for fueling. Long ascents, for example, require more energy, so plan to slightly increase your carbohydrate intake during those times. On the other hand, fast descents offer few opportunities to refuel, so it might be wise to plan your nutrition intake before reaching them. Use your personalized plan from the Nutrition Calculator to organize your fueling strategy effectively.

Training in Race-Like Conditions

Try to include at least one long run with elevation and duration similar to your race. It’s the perfect opportunity to test your nutrition strategy and see how your body responds.

For longer or ultra-distance races, it’s often hard to fully replicate race conditions in a single session. In that case, spread the volume and elevation over several consecutive days, like a back-to-back training weekend, to simulate the demands of the race.

Mimic the aid station setup

If aid stations are spaced far apart, practice fueling at the same intervals in training. And always carry enough fuel to meet your needs between stops.

This approach helps fine-tune your strategy and gives you the confidence to show up ready.

Summary: Your gut is a muscle, train it like one

Gut training is a progressive approach that takes time and adaptation. Don’t get frustrated if you don’t immediately reach your nutrition goals during training. Every athlete has a unique ability to absorb nutrients, and the key is to make steady progress week by week.

Three essential points to remember: Hydration is key: a well-hydrated gut functions better and reduces the risk of digestive discomfort.

• Hydration is key: a well-hydrated gut functions better and reduces the risk of digestive discomfort.
• Stress impacts digestion: the more relaxed you are, the better your digestive system will absorb nutrients. Test your strategy under race-like conditions to build confidence.
• Consistency makes the difference: each gut training session improves your tolerance and ability to fuel during exercise. No surprises on race day: don’t try using a new product during the race. Stick with what you’ve tested in training
  

By incorporating these principles into your training, you give yourself the best chance to avoid digestive issues and optimize your performance on race day. Now it’s your turn!

FAQ

When should I start gut training and for how long?

Ideally, begin at least 3–4 weeks before your race. For best results, train for 12 weeks to build tolerance and avoid discomfort, especially if you are aiming for a high-carb nutrition strategy (above 60g/h).

How do I train my gut to handle fluids?

By gradually getting your body used to drinking during exercise, you improve the process by which your stomach moves liquids into the intestine. Over time, this helps improve digestion, reduce discomfort like bloating, and optimize nutrient absorption.

To improve your digestive tolerance to liquids, start by gradually increasing your liquid intake. Slowly increase the amount of liquid during each session, aiming for a volume that represents about 20 to 30% of your total hydration goal per hour, depending on your needs.

Why is it important to test your race nutrition in advance?

Testing your nutrition helps you:

• Confirm your carb and energy targets are well tolerated
  

• Avoid unpleasant surprises with flavor or texture
  

• Support recovery and reduce muscle damage between sessions