For today we have several studies linking increased intestinal permeability or leaky gut syndrome to intense exercise.
„It is concluded that
(a) ibuprofen but not aspirin ingestion during prolonged exercise may increase gastrointestinal permeability and lead to GI symptoms, and
(b) prolonged exercise alone can produce GI symptoms.”
“Running at 80% Vo2max increased (P < 0.05) small intestinal permeability compared with rest, 40, and 60%Vo2max” – rest or slow pace run is better for your intestinal barrier than fast run, the induced leaky gut syndrome did not result in gastrointestinal symptoms though.
In this study Effect of moderate exercise on Crohn's disease patients in remission the researchers let Crohn’s patients as well as helthy controls to exercise for one hour at 60% VOH max and measured changes in intestinal permeability along with other gastrointestinal parameters. Concluded that this exercise did not induce leaky gut :”Moderate aerobic exercise has no significant effect on the gastrointestinal parameters examined. “
Gastrointestinal permeability during exercise: effects of aspirin and energy-containing beverages tested the effect of aspirine and sugary/glutamine energy drink on leaky gut provoked by exercise. Concluded that A (Aspirine) ingestion gets the leaky gut worse and neither the energy drink nor the added glutamine made it any better:
„results indicate that gastroduodenal and intestinal permeability increase after A ingestion during prolonged running and that ingestion of a CHO beverage attenuates the gastroduodenal effect but not the intestinal effect. Furthermore, addition of G to the CHO beverage provided no additional benefit in reducing gastroduodenal or intestinal permeability.”
“During exercise, symptomatic subjects have a longer OCTT and a higher intestinal permeability, which is more pronounced during running than during cycling.”
“There is reason to suggest that long-distance running affects the integrity of the gastric and the intestinal mucosa.”
And none of this is any different to your best friend:
„Dogs from three racing teams were examined before (pre) and immediately after (post) completing a 1770-km sled dog race in approximately 11 days.”
“Dogs with abnormal gastric endoscopy results (61% of finishers) had higher serum cortisol concentrations than dogs with normal endoscopy results (P=0.0007). We have demonstrated concurrent hypercortisolaemia and gastrointestinal barrier dysfunction with no correlation of the two. Thus, our data do not provide support for the hypothesis that increased serum cortisol concentration causes exercise-induced gastrointestinal disease.”
Just imagine: 6 out of 10 dogs with GI problems after finishing the race. Where are the animal right fighters?
Last paper Is the GI System Built For Exercise? is a thorough review of the subject of intense exercise and gastrointestinal problems. It links leaky gut induced by strenous exercise to heat and dehydration: „Mild to moderate exercise does not alter digestive function“
Further notes: ”Although any one of these stresses (exercise, heat, dehydration, NSAIDs), if severe, can produce tissue damage, it is usually the combination of two or more that initially produce GI symptoms and gut-barrier dysfunction. Evidence that exercise can impair gut-barrier function includes studies that show GI bleeding, endoscopic observations of mucosal lesions including hemorrhagic gastritis and ischemic colitis, increased intestinal permeability, and the development of systemic endotoxemia.”
The following statement may be valid for a healthy sportsman but somebody with leaky gut syndrome should be way more careful in getting involved in half marathon run which is an equivalent of 2 hours on 80% VO2 max:
“Thus it is concluded that for the vast majority of situations requiring even heavy (70–80% VO2 max) and prolonged (1-2 h) work, the GI system is built for exercise. The capacity to perform this amount of exercise, without detrimental effects, also includes the colon. Chronic exercise is associated with clinical benefits to the colon, which may also show signs of trainability. On the other hand, when heavy exercise becomes prolonged, performed in the heat, and the overall stress is exacerbated by dehydration, GI symptoms emerge, gut barrier function can become impaired, and tissue damage, including necrosis, can occur.”
My conclusion would be that if you are trying to heal your leaky gut intense exercise might not be a good idea. Either rest or get involved in moderate (40-60% VOH max), short term (below 30 minutes) exercise, cycling is better than running, do not overheat and stay well hydrated.