For all the many amazing benefits of running, there are quite a few unfortunate side effects.

For one: Running can give you, y'know, the runs.

A five-miler can grind your gears—that is to say, your gastrointestinal system—which often means that runners have to plan their running routes around restrooms, or keep the first couple miles close to home, lest you risk defiling some poor stranger's lawn like Arnold Schwarzenegger in the middle of Predator filming.

The culprit behind these shitty situations? For one, you've got less blood flowing to your gut, since it's surging to your legs and heart, which can limit your body's ability to digest. But an even more nefarious villain: "FODMAPs," a category of carbohydrates that your budy can struggle to digest.

FODMAP stands for "fermentable oligosaccharides, disaccharides, monosaccharides, and polyols". These carbs heighten your risk for runner's diarrhea, according to a study published in the journal Medicine & Science in Sports & Exercise. These are short-chain (not complex) carbs that can lead to gastrointestinal distress, because they're not easily or completely digested in the upper portion of your gut, researchers say. When they get to your large intestine, they're fermented by gut bacteria, forming gas.

To be more specific:

  • Oligosaccharides include at least .3g of fructans
  • Disaccharides include at least 4g of lactose
  • Monosaccharides include at least .2g more fructose than glucose
  • Polyols include at least .3g of sorbitol, xylitol, and mannitol

Most of the time, unless you have irritable bowel syndrome, FODMAP foods are pretty harmless. But they can be troubling for endurance athletes. In the study, researchers asked 11 competitive runners with self-reported exercise-related GI symptoms (e.g. bloating and diarrhea) to eat either a high-FODMAP diet or low-FODMAP diet for six days. During the week, they followed a prescribed training plan. Once completed, the runners took one day off, then repeated the procedure with the other diet.

For the most part, athletes experienced less GI discomfort during workouts on the low-FODMAP diet. Not to get too graphic, but they noted reduced flatulence, a lessened urge to run into the nearest bathroom stall, and fewer instances of diarrhea during exercise.

So: What are better options? The most common low-FODMAP foods, according to The IBS Elimination Diet and Cookbook, include:

  • Nut milks and aged cheese
  • Small amounts of berries, grapes, melon, bananas, and citrus fruit
  • Fruits and vegetables like leafy greens, tomatoes, cucumbers, carrots, peppers, and small amounts of sweet potatoes, squash, and zucchini
  • Small amounts of sweets made with real sugar: 100% pure maple syrup, stevia, dark chocolate
  • Tofu, tempeh, chickpeas, lentils, and edamame
  • Small amounts of nuts and nut butters
  • Leafy herbs, lemon, lime, mustard, oil, and vinegar
  • Beer, wine, clear liquor, and whiskey
  • Espresso, green and ginger tea

"For athletes who are at their wits' end trying to deal with exercise-associated GI distress, this could be a novel tool for possible symptom reduction" around races and long runs, says lead study author Dana Lis. But sticking to "a full low-FODMAP diet for an extended period is rarely advised and could lead to unnecessary diet restriction."

We recommend meeting with a sports nutritionist to create a safe meal plan, but avoiding high-FODMAP foods before your run can certainly be a good start. Not sure what that means? Click through the gallery for a primer on what to avoid when you're about to head out for a run.