You're not alone if your long runs give you the uh, runs of the digestive kind.

Credit: Illustration: Aad Goudappel

I always have to stop at a bathroom on long runs! How can I avoid it?

You're not alone. Runner's diarrhea is a real thing. Though doctors aren't exactly sure why it happens, food does seem to move more quickly through your colon when you run, which can bring on, well, runs of the digestive kind.

Limiting your fiber intake the day before you have an extra-long sweat session can help (that means going easy on normally good-for-you foods like whole grains and beans). So can avoiding caffeine the day you hit the trail or treadmill and refraining from eating two hours prior. Also, be judicious with energy gels, bars and chews; some people find that these products give them digestive problems. Weirdly enough, dehydration can also lead to diarrhea sometimes, so it's crucial that you load up on water before and after your run.

Try these dietary tweaks before you resort to taking an over-the-counter antidiarrheal medicine—they're fine in a pinch, but I don't recommend using them regularly, since they can cause constipation.

Health's medical editor, Roshini Rajapaksa, MD, is associate professor of medicine at the NYU School of Medicine and co-founder of Tula Skincare.