As Ms. Edwards and her colleagues demonstrated in a separate small study published last year, intestinal damage can be correlated with the intensity of exercise and isn’t specific to running. When compared with runners, cyclists showed similar levels of damage when exercising at similar intensity levels, although they reported fewer overall symptoms of gut discomfort. This damage mostly occurs during high-intensity efforts, Ms. Edwards said, when exercisers were working out at 80 percent of their bodies’ VO2 max (a measurement of the ability to absorb and use oxygen, loosely tied to effort), compared with when they were working at 60 percent.
“Anything below a moderate intensity, it’s unlikely you are going to get much damage,” Ms Edwards said.
How to avoid it
Thankfully, there are ways to avoid runner’s gut, Dr. Borowski said. When running long distances, such as when training for a marathon, you need to eat enough to fuel your body, but not so much that it causes gut issues, which is tricky. “What to eat and when to eat is really difficult when it comes to marathon training,” she said.
Two to three hours before a run, eat foods that contain simple carbohydrates, like bananas, rather than foods with lots of fiber or complex carbohydrates, such as berries or whole wheat bread.
Training the gut for a long run can be every bit as important as training your legs. Practice what to eat and drink while training, and remember that a race will be more intense than most training runs. Pay special attention to how you feel during training runs done at race pace, rather than just during long, slow runs. On race day, anxiety can also contribute to stomach issues, which is why Dr. Borowski advised not putting any extra strain on your gut and to stick with the usual foods you eat before runs, rather than trying something different. It’s also important to stay hydrated.
A recent study of 46 people concluded that compression socks may help, too. In the study, published in September in the Journal of Strength and Conditioning Research, researchers from Australia looked at the associations between wearing compression socks and intestinal damage during a marathon. Compression socks, which apply pressure to the outermost muscles of the legs, are known to improve circulation.
In the study, those who wore compression socks while running a marathon showed lower levels of a blood marker for intestinal damage than those who did not. Wearing compression socks may not thwart runner’s gut, Dr. Wu said, but it is a relatively simple action that may help minimize the effects.
“If we can improve the blood flow and increase circulation to the deeper parts of the body, then we should be able to promote blood flow back into our digestive system,” said Dr. Wu, who was one of the study authors. “That can help to decrease or reduce the amount of damage that’s done to our gut during high-intensity exercise.”
Rachel Fairbank is a freelance science writer based in Texas.