If you run, you’ve probably experienced occasional digestive discomfort. At best, this annoying little side effect can limit your performance. At worst, it can become so intolerable that it forces you to abandon your run altogether. In severe cases, it can even present health risks. “Gastrointestinal problems are common, especially in endurance athletes, and often impair performance or subsequent recovery,” notes an analysis published in Sports Med. “Generally, studies suggest that 30–50% of athletes experience such complaints.”

No fun at all. Luckily, there are certain foods that can help mitigate the effect—and optimize your performance. Read on to find out exactly what you should be eating before you hit the road for max results.

Running and digestion

Here’s what’s going on to cause the upset: When the body exerts physical effort, it redirects blood to the muscles in order to supply them with as much oxygen as possible. This redistribution reduces blood flow to the digestive system, disrupting its function. This can happen during any intense physical activity, and is the reason that most of us were told not to swim right after eating as children.

But running is also a high-impact sport, which creates a bit of a double whammy—literally. Each step against the ground results in a shockwave of vibrations that travels up the legs to the body’s digestive organs, creating discomfort and cramping.

The role of diet and timing

Nutrition is the cornerstone of fitness—and for runners, timing is everything. To give the body adequate time to digest before a run, here’s a good rule of thumb: Wait two to three hours after a meal, and 30-60 minutes after a snack. Avoid foods that are high in fat, protein, and fiber—all of which are extra difficult and time-consuming to digest.

Just as some foods can make digestion difficult before a run, other foods can optimize energy and boost performance. A good pre-run meal or snack should include easy-to-digest carbohydrates to support the body and boost performance, as well as protein to help stabilize blood sugar. “Appropriate nutritional choices can reduce the risk of gastrointestinal discomfort during exercise by ensuring rapid gastric emptying and the absorption of water and nutrients and by maintaining adequate perfusion of the splanchnic vasculature [abdominal nerves],” the aforementioned review notes.