Doctors and researchers don't know exactly how many female runners suffer from exercise-induced diarrhea, but they estimate that it afflicts a third to a half of those who are training or racing at any given time.

One reason for the distress could be that our delicate digestive organs aren’t getting enough blood during exercise—a condition known as ischemia. In the body’s ongoing attempt to manage its resources optimally, the heart pumps oxygen and nutrients to the organs and systems that need them the most. During a long or intense run, the skin and large muscles the most urgent recipients; the intestines become a lower priority. In this instance, our glutes have more of a need for oxygenated blood than our stomachs. In fact, during a peak physical effort, blood flow to the internal organs can decrease by as much as 80%. The resulting lack of blood flow to the intestines compromises the functions of their mucosal lining, making it more permeable and prone to malfunction.

The frequent use of non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen may also be triggering or exacerbating the problem. While there is a place for their occasional use (for pain and inflammation), they can cause problems anywhere along the GI tract, from the esophagus to the colon.

In a healthy gut, epithelial cells in the gastrointestinal tract (similar to those found in our skin) hold tightly together to protect large molecules from passing through the intestines and into the bloodstream. NSAIDs make the mucus lining the intestines more permeable, which can contribute to the onset of gastritis (gut inflammation) and ulcers (small sores on the stomach lining), among other things. Since these drugs work partly through reducing blood flow to the digestive system, their harmful effects should be considered carefully by athletes. One study that found that damage markers in the digestive system were twice as high in runners who took anti-inflammatory medications compared to those who didn’t.

It’s likely that dietary choices, however, play the most important role in the incidence of digestive distress many otherwise healthy athletes experience during or after a run. The large—and ever-increasing—body of evidence against the reliance on ‘healthy’ whole grains is compelling. And it’s not just because they contain dietary fiber, a common and well-recognized cause of diarrhea. Nature designed the outer husks of all grains to be protective, arming them with a mild toxin known as phytic acid. Unlike berries and other plants that need to be consumed in order to reproduce and spread, grains were designed to propagate by being blown by the wind, not eaten. Beans and legumes also contain phytic acid in smaller amounts.

Could phytic acid be a problem for you? The best way to find out is to completely eliminate grains, beans from your diet for at least 2 weeks but preferably 30 days. Many women will experience significantly relief. If there’s no change in your symptoms, NSAID’s may be the culprit. Or you may be suffering from underlying food sensitivities or allergies that have gone undetected and/or a leaky gut and intestinal inflammation that needs some additional support and time to heal.

Have you ever suffered from exercise-induced diarrhea? What steps did you take to solve it? Did you find that eliminating certain foods was ultimately the answer? Please share your insights and experience in the comments section below.