Gastrointestinal Issues and Exercise
Endurance athletes both running and cycling experience symptoms of gut discomfort as the intensity of their training increases and with competitive events. These symptoms can sometimes make competing a literal pain in the butt. However, there are ways that endurance athletes can support their bodies that prevent or reduce some of these symptoms.
High-intensity exercise causes damage to the gut in a few different ways: altered GI blood flow, mechanical trauma, heat, and NSAID use. As exercise intensity increases the body shunts blood away (causing gut ischemia) from the digestive tract to the cardiac and skeletal muscles. This causes any foods in the GI tract to be insufficiently digested resulting in lower nutrient absorption and the stool moving more quickly through the GI tract. When exercise is finished, the blood then returns to the GI tract tissues often causing damage to the endothelium which can cause cells to rupture and blood to be in the stool. GI bleeding can also be caused by mechanical injury from posture (cyclists), or acceleration and deceleration forces (cecal slap syndrome). NSAID use increases the chances of having a serious adverse GI event 3-fold. These medications aggravate any pre-existing exercise-induced small intestinal injury as well as inducing gut barrier dysfunction. Increased core temperature can also damage the gut endothelium.
These damages often result in “Runner’s Gut” or gastrointestinal bleeding (GIB). Nausea, vomiting, diarrhea, and bloody stool are poor performance enhancers. So, let’s look at some tips for staving off these symptoms.
Stay Hydrated! Starting training or events sufficiently hydrated will help keep your blood pressure regulated and help with core temperature regulation. Feel free to use hydrating powders or drinks that contain magnesium glycinate. Be careful, some forms of magnesium can cause loosening of the stools and you don’t want those (magnesium citrate). AVOID highly concentrated carbohydrate solutions!!! These will aggravate dehydration and often cause diarrhea.
Increased nitric oxide availability improves gut blood flow, you can increase this by eating nuts, seeds, legumes, whole grains, yogurt, raw spinach, cottage cheese, papaya, zucchini, watermelon, cantaloupe, cucumbers, beets, poultry, and beef. These foods contain arginine, glutamine, or citrulline which boosts nitric oxide. (*note: raw spinach does not allow for the absorption of calcium and iron and regularly ingesting large amounts of raw spinach predisposes you to kidney stones. So balance your intake of raw and cooked spinach).
There is beginning to be some research that foods with galactooligosaccharides, fructooligosaccharides, ALA, resveratrol, and/or DHA could be protective of intestinal endothelial cells from heat damage. These foods are good for you anyways, so including legumes, cashews, pistachios, hummus, soy milk (from whole soybeans), oat milk, onion, garlic, asparagus, banana, artichoke, flaxseed, pumpkin seed, tofu, walnuts, peanuts, berries, grapes, chia seed, and salmon could serve multiple purposes.
Probiotics have been found to reduce the gut ischemia and the related leaky gut, so incorporate pickles, olives, sauerkraut, chia seeds, hemp hearts, pickled red onions, cottage cheese, nutritional yeast, sourdough bread, kefir, kimchi, yogurt and other probiotic FOODS into your daily routine. This benefit has only been found with long-term use, so making this a regular habit is a must. (*note: probiotic supplements have the opposite effect by disrupting your natural microbiome. Probiotics are best ingested in food form).
A liquid meal prior to running has been found to reduce the blood shunted away from the GI tract. Consider testing out a smoothie or protein shake prior to training.
DON’T use NSAIDs pre-race.
Compression socks have been found to reduce gut ischemia. In a study conducted on runners, the ones that wore compression socks during their race had less GI distress.
The Point:
Good nutritional habits can help reduce the gastrointestinal distress you experience with high-intensity endurance training. Regular intake of probiotic-containing foods, prioritizing hydration and nuts, seeds, and legumes (among a few other ergogenic foods) will give your body a chance at dodging the runner’s gut and bleeding.