Over the long term, exercise helps maintain a healthy gut, allowing you to better absorb nutrients, says Florence-Damilola Odufalu, a gastroenterologist at the University of Southern California’s Keck School of Medicine. Physical activity increases our production of a chemical called nitric oxide, which helps relax the muscles in our intestines and prevents inflammation.
Working out also is well-known to promote mental health. Your intestines are lined with nerve cells that communicate with your brain and respond to stress via neurotransmitters. Many researchers now consider irritable bowel syndrome (IBS) a disorder of the gut-brain interaction that is frequently triggered or exacerbated by stress, anxiety, or depression.
While people with digestive disorders may not be able to exercise comfortably during flare ups, when they can get physical activity in, it’s likely to be beneficial. It can reduce symptoms of depression and anxiety that trigger digestive flares.
“It should really be emphasized that there are a lot of beneficial effects on the body, the bones, mental health,” of exercise, says Djalal, all of which can improve outcomes in digestive disorders such as IBS and inflammatory bowel disease (IBD).
High intensity exercise
While light or moderate exercise is almost always helpful for digestion, intense exercise requires some caution.
“There’s an increase of blood flow all along the GI tract to allow the digestion to happen,” explains Djalal, and “when you exercise, the demand is elsewhere. It’s in your muscles, it’s in your lungs and it’s in your heart.” Essentially, your digestive system, your muscles and respiratory system start competing for blood flow.
When you’re exercising at a lower intensity, all the systems can share your blood flow and function effectively at the same time, but as the workout becomes more intense, your muscles, lungs and heart require more and more blood, leaving little for your digestive system. This makes it difficult for your body to digest anything during your workout.
When you’re exercising at a high intensity, your body is processing the oxygen from your heavy breaths to create energy, or ATP. In doing so, it also creates metabolic byproducts such as lactate and hydrogen ions. During light exercise, your body can easily clear these byproducts before they cause any problems, but as you start pushing yourself harder, eventually your body can’t keep up. Your digestive system might try to get rid of these byproducts by making you vomit. Costa explains that’s why you might see someone throw up even after a very short, but very intense, sprint race or you might feel nauseous after a particularly challenging workout.
Heat, dehydration, and bacteria
Heat can exacerbate digestive problems brought on by exercise. As your core temperature rises, blood flows away from your internal organs and out toward your skin to help cool you down.
Plus, any hard workout will make you sweat. If you’re unable to replenish the fluid and electrolytes you’re losing quickly enough, you’ll end up under-hydrated. This thickens your blood, slowing its movement and worsening digestive symptoms, explains Costa.
