Brush Border Insufficiencies in Endurance Athletes

Brush border insufficiency is a form of malabsorption that we commonly see in endurance athletes. This is primarily caused by damage to the intestinal lining and exercise-induced splanchnic hypoperfusion (EISH), which is a condition that reduces gastrointestinal blood flow. Overtime, EISH damages the brush boarder lining and decreases the absorption of nutrients. EISH is caused by exercise-induced gastrointestinal syndrome (EIGS), which is where the reduced blood flow causes oxidative stress, intestinal ischemia, and damages the intestinal villi. This causes increased permeability, enzyme dysfunction, and a decrease in nutrient absorption. Those who partake in prolonged, high-intensity exercises (runners, cyclists, ultra athletes) are more susceptible.

Signs and symptoms

• Darrhea

• Abdominal cramping

• Bloating

• Abdominal pain

• Excessive burping and gas

• Frequent urges for bowel movements

Ways to improve brush boarde insufficeiny

• Make sure to eat enough fiber

• Eat probitoics daily (miso, kimchi, sauerkraut, kombucha)

• Eat balanced meals

• Stay hydrated

• Make sure to get enough electrolytes

• Reduce stress

• Reduce irritants (like certain gel)

Additionally, training our gut shows promise. A 2025 article found that slowly increasing high glycemic index foods during training over the course of 2 weeks supports sodium-glucose cotransporter 1 (SGLT1), which is the main pathway for sugar and glucose absorption. Overall, the best way to support athletes is to make personalized plans that work for them by doing trial and error mock races to see what works and does not work.

Resources:

Costa, R. J. S., Snipe, R. M. J., Kitic, C. M., & Gibson, P. R. (2017). Systematic review: exercise-induced gastrointestinal syndrome-implications for health and intestinal disease. Alimentary pharmacology & therapeutics, 46(3), 246–265. https://doi.org/10.1111/apt.14157Links to an external site.

De Oliveira, E. P., Burini, R. C., & Jeukendrup, A. (2014). Gastrointestinal complaints during exercise: prevalence, etiology, and nutritional recommendations. Sports medicine (Auckland, N.Z.), 44 Suppl 1(Suppl 1), S79–S85. https://doi.org/10.1007/s40279-014-0153-2

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

Sumi, D., & Suzuki, Y. (2025). Gastrointestinal function and microbiota in endurance athletes. Frontiers in physiology, 16, 1551284. https://doi.org/10.3389/fphys.2025.1551284