Exercise is universally recommended to maintain a healthy lifestyle. However, there may be a point where too much exercise is harmful. A review of the science has determined that there is such a situation that causes damage to your gut.
A new term “exercise-induced gastrointestinal syndrome” is being used to describe a complex response to exercise that disturbs and compromises gastrointestinal function. Typical symptoms of this syndrome include bloating, belching, and urge to regurgitate. More seriously, it can lead to malabsorption of nutrients and systemic inflammation. Exercise-induced gastrointestinal syndrome is deemed to be the result of interactions between your gastrointestinal tract and the circulatory, immune and nervous systems.
A review of the scientific literature on this topic has yielded some insights on this syndrome.
The first observation was that exercise can result in intestinal injury of the epithelial cells from restriction in blood supply. They found that people who exercise for over one hour had significant increases in the marker, intestinal fatty-acid binding protein (I-FABP). Greater increases in I-FABP were found in people who had over 90 minutes of vigorous exercise in the heat. Heat stress accelerated the incidence of injury. This condition results in malabsorption of food nutrients.
The explanation for this is simple. When you exercise, your body sends blood to the muscles that need the oxygen load. It does that by taking it away from your gastrointestinal tract. A prolonged condition like this results in your intestinal cells getting oxygen starved and dying.
A second observation was that intestinal permeability (leaky gut) increases with the magnitude of exercise. This is an inflammatory response to exercise and heat. A leaky gut allows bacterial molecules called lipopolysaccharides to go from the intestine into the blood stream. Again, periods of exercise over one hour see a spike in leaky guts.
We've often heard the advice to not exercise with a full stomach. The paper supports this because they found that exercise bouts of low to moderate intensity, of less than one hour, promotes gastointestinal mobility. However, more prolonged exercise causes a disturbance in gastric mobility. Having food sitting in your gut will lead to bloating from the sugars being fermented.
The paper certainly provides strong evidence that exercising for over one hour or in the heat can have significant negative health effects. The authors do recommend prevention strategies for whenever you are exercising. The following are seen to reduce exercise-induced gastrointestinal syndrome:
1- Maintain good hydration – include electrolyte replacement
2- Consume 15 grams of carbohydrate before exercising – avoid protein during exercise
3- Go gluten-free
4- Avoid NSAIDs – they are gasrtointestinal irritants
5- Consume anti-oxidants, L-arginine, and L-citruline
The paper concludes that as exercise intensity and duration increases, there is considerable increases in indices of intestinal injury, permeability and impairment of gastric emptying, slowing of small intestinal transit and malabsorption. The addition of heat stress appears to exacerbate these markers of gastrointestinal disturbance.
Exercise stress of over one hour appears to be the threshold whereby significant gastrointestinal problems occur, irrespective of how fit you are. Gastrointestinal symptoms are common and can limit your ability to do exercise but they can be reduced by using nutritional supplements.
