It’s no secret that running can do a number on your digestive tract, especially when it comes to long races. While gut issues not only leave you feeling terrible, they can also decrease the amount of energy your body has to keep competing – and performing well.

While even regular long runs can send your stomach sloshing, ultra-endurance races can be especially bothersome for gastrointestinal issues.

In fact, according to a review published in Research in Sports Medicine anywhere from 60 to 96 percent of ultra-athletes experience bothersome upper and lower gastrointestinal symptoms in workouts lasting four or more hours. In particular, ultrarunners tend to be more prone to upper gastrointestinal issues, like bloating, belching, stomach pain, urge to vomit, vomiting and nausea, says Ricardo Costa, Ph.D., senior researcher in exercise physiology, metabolism, and dietetics at Monash University in Australia.

That’s because during endurance exercise, your blood flow gets redistributed to the working muscles, which results in low blood flow to the gut.

“Additionally, the natural stress response to exercise (fight or flight response) shuts-off gut function and blood flow to the gut,” Costa says. “These two mechanisms have the potential to damage the gut and impair its function.”

The urge to hurl could put a serious damper on your ultra. But thankfully, there are some ways to keep your gastrointestinal tract in check – it just requires a little pre-planning. According to a recent study, how you eat both during the race and in the weeks leading up to it is the most important factor to calm your gastrointestinal tract down during ultra-endurance activities.

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How to Eat Before Your Race

The review reported that “gut training” – or consuming substantial amounts of carbohydrates during your race training to build up your gut’s tolerance for carb consumption during your actual race – is key to prepping your gastrointestinal tract. So is finding the perfect balance of carbs and fat to consume while doing it. When runners attempted to gut train each day for two weeks before their event, consuming 90 grams of carbs (a 2:1 glucose-fructose blend) per hour while running at 60 percent of their VO2 max, they experienced a substantial decrease in gut issues.

Then, when you get closer to the big event, that’s when carb loading comes in.

“Older protocols [for carb-loading] are one week, more refined protocols say three days,” Costa says. “However, evidence for two days—provided exercise is kept to a minimal and carbohydrate intake is 10 to 12 grams per kilogram of body weight per day – has shown the best results.” That’s in accordance with the current American College of Sports Medicine (ACSM) nutrition and performance guidelines.

When it comes to fat, the review took a look at ultra athletes who went on low carbohydrate/high fat or ketogenic diets, eating less than 50 grams of carbohydrates per day for over three weeks. It found that such diets did increase total fat oxidation rates during exercise, but consistently caused a reduction in exercise economy – meaning the participants lacked the energy for their super endurance exercise, leading to worse performance than the high or average intake carb groups. So the increase in fat oxidation didn’t translate to any performance improvements.
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How to Eat During Your Ultra

As for during the race? Carbs are king for fuel, but the amount and type consumed is crucial. Too much or too little, fibre-rich carbs, and those mixed with protein and fat, for example, could actually increase gastrointestinal symptoms.

Research findings support the consumption of 1 gram per kilogram of bodyweight per hour for men, and 0.8 grams per kilogram of bodyweight per hour for women during ultra events.

If you’re just exercising for a few hours, water is sufficient. For longer exercise bouts – say, up to three hours – stick with liquid carbohydrate sources instead of solids for the best gut-soothing results. That’s because liquids have a lower gastric load and empty quicker from the stomach than semi-solids like gels or solid foods do, says Costa.

But if you’re running an actual ultra, you’ll need to add in real food, not just liquids. Getting all of your nutrition via liquids for something as prolonged as a 24-hour ultra can increase your risk of exercise-induced hyponatremia, which is a low concentration of sodium in your blood. Plus, consuming only liquids can make you nauseous, too, he says.

Still worried about some gastrointestinal issues during your race? Here are a few more stomach-soothing tips you can try.

Drink cold water.

The temperature of the water you drink could also play a role, especially if you’re running in the heat.

The review found that cold water (between O°C and 7°C) consumed pre-exercise and frequently during a two hour run in 35°C weather moderately reduce gastrointestinal symptoms compared to runners who drank water that was warmer (20°C).

Choose your pain reliever wisely.

Taking NSAIDs has also been found to cause GI issues in ultrarunners by causing erosion of the mucosal lining along the gastrointestinal tract, which can lead to gastrointestinal ulcers, bleeding and diarrhea.

You should avoid taking them the day before, immediately before, and during your race. The pain reliever acetaminophen has been found to be less hard on the GI tract.

Don’t swallow your sports drink.

The review also found that if you’re prone to gastrointestinal issues, you can try swilling your carbohydrate drink instead of actually swallowing it . The review found that it creates a placebo-type effect that fuel is coming – even if it doesn’t.

There are glucose receptors in mouth, which directly inform your brain that rapid fuel is on the way, which blunts your perception of fatigue, says Costa. This can be especially helpful later in a race when you’re about to hit the wall, but feel like your stomach is too sensitive to take in any food or beverage without rebelling.

This article originally appeared on runnersworld.com.

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