Every sport has its own nutritional considerations. For example, the needs of a 100 meter swimmer are very different than a 10K open water swimmer - even though both are swimmers. The same is true of a marathon runner compared to a long distance triathlete - even though both run 26.2 miles. While nutrition is important for every type of athlete, the nutritional demands of training and racing are different for every athlete and depend on factors such as distances and intensities being performed, as well as on the type of terrain, temperature and altitude.
With respect to endurance and ultra endurance events, athletes experience numerous physiological stressors which can have significant health and performance consequences. Certainly, proper fueling and hydrating can minimize the risk of issues. From glycogen depletion and dehydration to muscle damage and GI issues, many athletes have a poor understanding of how to fuel appropriately during long distance activity - or intentionally underfuel for fear of gaining weight.
GI issues are very common among endurance athletes. Symptoms like bloating, cramping, nausea, diarrhea, vomiting and reflux are some of the most common reasons why athletes struggle to perform to their abilities on race day.
The GI (or gastrointestinal tract) plays a very important role in how your body performs on race day. This series of connected organs is the only way to deliver carbohydrates and fluids to the blood during long distance activity. Because the gut is very adaptable, you need to take the time to "train the gut" in order to improve stomach comfort, improve gastric emptying and absorptions and reduce symptoms of GI distress - all in an effort to improve endurance performance.
To help you train your gut, here are a few key considerations:
- It can take between 6-10 weeks to improve stomach comfort. You should be preparing for your 'race day' nutrition plan at least 10 weeks out from the event by practicing nutrition similar to race day during your longest training sessions. Start on the low end and gradually work your way up in calories/fluid. You can begin to train your gut by consuming smaller amounts of sport nutrition during shorter workouts to get comfortable drinking/eating while exercising, while also experimenting with different products/flavors.
- Dehydration makes GI issues worse. Dehydration slows down gastric emptying. Make sure to consume well-formulated sport drinks with adequate fluid. Also, be mindful to adjust your pacing and nutrition intake for hotter conditions (more dilute/electrolyte rich) when the gut will be more compromised due to the heat. Because most athlete underhydrate and underfuel while running, it's to your best interest to use a hydration belt/pack when you run.
- There are two specific protein transporters (SGLT1 and GLUT5) that allow for carbohydrate absorption. When your sport drink contains glucose, sucrose, maltodextrin or starch, exogenous carbohydrate oxidation peaks ~60g/hr (~240 calories). This is because the SGLT1 transporter becomes saturated. Because fructose uses a different transporter (GLUT5), adding fructose to a sport drink can allow for higher oxidation rates (up to 90g/hr). And research shows that up to 90g of a 2:1 glucose/fructose ratio also improves performance. To increase the capacity to absorb carbohydrates, it's critical that your sport drink has the right formulation. Simply eating/drinking whatever you want, whenever you want is not what it means to "train the gut."
- A higher carb diet (for ~2 weeks) will result in the upregulation of SGLT1 transporters. Therefore, if you consume a low carb diet and then attempt to train the gut with a high amount of carbohydrates, the higher carb intake will not be well absorbed. Additionally, a keto diet may impair the muscle's ability to use glycogen for oxidation, compromising the use of a more economical energy source when the oxygen supply becomes limiting when effort exceeds >80% maximal aerobic capacity.
- You can't blame everything on sport nutrition. Pre-workout/race fat/fiber intake, highly concentrated carb solutions (ex. putting 3-4 hours worth of nutrition in one bottle), poor pacing, poor terrain management, jostling of organs, posture, inefficient movements, stress/nervous and redistribution of blood flow away from the gut and to the skin and working muscles may cause GI issues.
If you've had negative experiences with sport nutrition, you are not alone. But don't let these experiences stop you from consuming the fuel that your body needs to stay healthy and to perform at its best. Remember - your body is very adaptable. Like training your muscles, you need to train your gut.
https://www.gssiweb.org/sports-science-exchange/article/training-the-gut-for-athletes
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5371619/
https://physoc.onlinelibrary.wiley.com/doi/10.1113/JP278928