Today, let’s address training the gut and fueling during your run. This is a digestive health topic that’s pertinent to endurance athletes, particularly runners. While many athletes are wrapping up their fall season right about now, taking a little seasonal workout slow down, and/or making race plans for the new year, it’s a good time to also start thinking about nutrition and how it impacts performance for the months going forward.
Underfueling during exercise and throughout the day
Generally speaking, the general trend among runners, as compared to cyclists and triathletes, is that runners tend to under fuel during activity, despite ample science making a case for adding an energy source during long runs. It’s also very common for endurance athletes across many sports to be under fueling throughout the day(s) in their entire eating pattern, for just how much they are moving their bodies.
There are a few reasons why runners in particular might be under fueling during activity specifically:
- Blood flow changes during exercise, leading to more blood flow to the skeletal muscle and extremities and less blood flow to the GI tract, along with a shift in the GI nervous system control. These two combined can lead to more exercise-associated GI symptoms, which many hope to avoid.
- Additionally, exercise load including intensity, type of exercise, and duration, can lead to more GI symptoms. Runners especially tend to suffer more because running is an impact sport and there is a lot of jostling of the GI organs while running. The longer and harder the effort, the worse and more frequent GI discomfort will be (2).
- Heat and humidity also tend to increase GI symptoms (2).
- Another reason may be due to confusion and/or not understanding how fueling can help. A recent conversation with a runner revealed that he had initially believed that not fueling during any training runs when he was marathon training would be beneficial because he theorized that if he then added fuel only on marathon race day, the fuel would work better. This is certainly not the only belief that an individual can have.
Training the Gut
It’s quite common for athletes to say they don’t tolerate fuel so they don’t add any hydration or energy source during running or training. Additionally, many athletes also avoid eating or drinking before training because if they do so, it also causes GI distress.
Contrary to the belief that one should avoid fueling before or during training due to currently experiencing GI discomfort, nearly everyone can benefit from training the gut (1). So first, what is training the gut?
It’s the digestive system version of what you’re doing day after day and week after week with training the body to run longer distances and more intense paces. Back when I began running, there wasn’t any information available on the topic of “training the gut,” but it was a common recommendation to take carbohydrate fuel during training and races longer than about 90 minutes. That recommendation hasn’t changed, but depending on what event you’re training for, it will be helpful to train the gut to tolerate more fuel. This is a gradual process performed over several different long efforts rather than just testing out your race day fuel once or twice before an event, or not fueling at all.
Why is training the gut important?
Ever watch (or simply read about) one of those eating competitions like “how many hot dogs can you eat in a certain amount of time?” The amount of food consumed by the top competitors is fairly unbelievable, right? You can bet those individuals cannot eat like that all the time. They have to train their body to tolerate that amount of food. That is an extreme example, but when we look at endurance sports, what we see is that when you fuel consistently and correctly, and depending on the length of time you’ll be competing and at what intensity, fuel A LOT during activity, what we see is better results during the event and better recovery in the days afterwards (3).
Let’s look at an example from athletics rather than eating competitions.
If you’re watching the Tour de France or any other professional cycling these days, amongst the top athletes in the sport of road cycling, staying in the peloton (or riding in front of it!) is almost as much a fueling competition as it is an athletic competition. Riders these days are training their bodies to tolerate upwards of 120 grams of carbohydrate per hour (3). The standard gel packet of endurance fuel has about 24-30 grams of carbs, so for reference that’s about five gels an hour, to give you some perspective.
While that level of fueling is not necessary for everyone for every context (intensity and time of activity matters a lot), it is the amount of fueling –and gut training to be able to take in that amount of sugar—that is leading to top results on the world tour level.
Some Practical Why’s for You
The body can only store a certain amount of glycogen (stored glucose or carbohydrates) in the muscle and liver, and for most endurance events that are lengthy and have some intensity, carbohydrate is going to be the primary type of macronutrient that your body is burning. When we fuel correctly with adequate carbohydrates during activity, you’ll be sparing yourself from depleting all the stored muscle and liver glycogen, and utilizing it from the fuel you ingest during activity instead. This is also why we see better recovery after exercise from those that fuel more during exercise – because the body doesn’t have to go to all the work of restoring as much of the depleted glycogen stores (3).
So what are the other benefits to training the gut?
Repetitive exposure to nutrition both before and during exercise leads to better tolerance of the fuel you’re consuming. Training the gut can also improve GI function during exercise, and reduce how often you might experience the all-too-common exercise-associated GI symptoms, as well as their severity. For all those athletes that have a finicky GI, some of these GI symptoms that gut training can improve or reduce include (2):
- Gut discomfort
- Upper GI symptoms like burping, belching, nausea and indigestion
- Carbohydrate malabsorption (ever feel like you’re fueling during an event and it’s simply not being absorbed)?
- Gut microbiome dysbiosis and inflammation
- Changes in GI motility (having to go urgently, or on the flip side, being constipated)
- Changes in capacity (how much food you can tolerate)
Likewise, the adaptations to training the gut around and during exercise can also result in improved performance (2). This is because consuming a higher carbohydrate amount both during exercise and as part of a daily eating pattern lead to enhanced glucose availability.
Learn More
In the coming weeks, I’m planning to continue this topic of fueling sports performance and gut training in more detail. Stay tuned!
If you’d like to know more, I work with clients in individual nutrition consultations, and as a Licensed Dietician / Nutritionist and Certified Nutrition Specialist, use medical nutrition therapy, integrative health measures, and a root cause approach to heal imbalanced health conditions.
Conditions I specialize in include all digestive health imbalances and disorders, endurance athlete sports nutrition, vegan/vegetarian diets, intuitive eating, and autoimmune diseases.
If you’d like to learn more about how you can improve your symptoms of imbalance, I’d love to speak with you in a quick phone consultation!
References
- Jeukendrup A. E. (2017). Training the Gut for Athletes. Sports medicine (Auckland, N.Z.), 47(Suppl 1), 101–110. https://doi.org/10.1007/s40279-017-0690-6
- Martinez, I.G., Mika, A.S., et al. (2023). The effect of Gut-Training and Feeding-Challenge on Markers of Gastrointestinal Status in Response to Endurance Exercise: A Systematic Literature Review. Sports Medicine, 53, 1175-1200. doi:10.1007/s40279-023-01841-0.
- Viribay, A., Arribalzaga, S., Mielgo-Ayuso, J., Castañeda-Babarro, A., Seco-Calvo, J., & Urdampilleta, A. (2020). Effects of 120 g/h of Carbohydrates Intake during a Mountain Marathon on Exercise-Induced Muscle Damage in Elite Runners. Nutrients, 12(5), 1367. https://doi.org/10.3390/nu12051367
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