The only thing worse than stomach trouble while running a race is the fact that a heavily trafficked porta potty is your only option for dealing with it.

Hence why you're looking for advice to avoid runner's stomach — the gastrointestinal (GI) distress some runners experience that can manifest as:

• A strong, immediate urge to use the bathroom
• Diarrhea
• Nausea
• Stomach cramps
  
  

"On race day, the last thing you want to deal with is a meal that sits in your stomach like a brick or causes inconveniently timed bowel movements," says Kim Lowry, sports dietitian at Houston Methodist. "Fortunately, there are steps you can take to help avoid runner's stomach and its particularly inconvenient symptoms."

What causes GI distress during long-distance running?

According to Lowry, the three primary contributors to runner's stomach are:

• The "jostling" nature of running
• The slowing of your gut motility
• Any race-day nerves you might have
  
  

"Just the simple mechanics of running are where the problems begin. Your body is moving up and down, sometimes rapidly — as is any food that's in your stomach. It's a lot of sloshing, shaking and jostling, which can lead to cramps, nausea or an urge to go," says Lowry.

Then there's the physiology of running. The reality being that, during a long run, proper digestion just isn't top priority.

"During exercise, your blood supply is redirected away from certain organs, such as your gut, to your muscles. On the one hand, this is a good thing. It means more oxygen and nutrients can be delivered to your hardworking muscles. On the other hand, reduced blood flow to your gut can affect how food moves through your digestive tract," explains Lowry.

Lastly, plain old nerves can affect your gut function, too. And, on race day, nerves are anything but uncommon.

"All of these factors can lead to your gut becoming distressed — especially if your body isn't used to it or if you've fueled with the wrong foods. There can also be some variability in how one body handles this stress compared to another," says Lowry.

For instance, your stomach might decide to...release its contents. Meanwhile, the person running next to you might be dealing with a stomach that's locked up instead, feeling the cramps and nausea that can arise as food continues to slosh inside the stomach.

The good news, however, is that — from how you prepare for a race to what you eat beforehand — there are several things you can do to help limit your chances of experiencing GI distress while running a race.

5 tips for avoiding runner's stomach on race day

Here are Lowry's tips for avoiding GI distress on race day:

1. Train your gut ahead of time

"Everyone's stomach reacts differently to a long run, and even simple carbs can give some people grief at first. Well before race day, be sure to give your body the time it needs to adjust to digesting food during exercise, as well as plenty of time to try out different foods in case your gut is more sensitive," says Lowry.

As a rule of thumb, avoid trying anything new on race day. In fact, Lowry recommends only eating foods you've tested and practiced with at least three or four times previously.

2. Carefully consider your meal plan

"You'll want to start being careful about your food choices at least three to four hours before your race. But, to play it safe, I actually recommend considering your dinner plans the night before, too," says Lowry.

Here's what Lowry recommends:

The night before the race: Try to pack in plenty of carbs and protein, while avoiding fibrous veggies. For instance, your meal could be:

• A burrito bowl with rice, chicken, bell peppers and mild salsa
• Chicken pasta
• Pizza topped with plenty of veggies
  
  

About three to four hours prior to the race: Choose a meal that's moderate in protein and high in simple carbs, such as:

• Peanut butter toast with a banana
• A fruit smoothie with Greek yogurt, honey and frozen fruit
  
  

An hour before the race: Top off your energy stores with some simple carbs. For instance:

• A banana
• Energy gel
• Energy waffle
• Pretzels
  
  

During your run, you'll need to refuel with 30 to 90 grams of simple carbs every hour, but you'll want to be careful about what exactly you're putting in your stomach — it needs to be simple carbs.

"I recommend energy gel or energy chews for refueling. They're not only easy to carry on the go, but they're typically designed to deliver simple carbs in a way that can help limit the chance of GI distress," says Lowry.

3. Avoid slow-digesting foods and common gut irritants

As mentioned, running a race can be stressful on your gut — so it's important to avoid anything that might potentially make your situation worse.

"Foods that are high in fiber, such as broccoli and cauliflower, and/or high in fat are harder for your body to break down — making them more likely to just sit and slosh in your stomach during a long run," explains Lowry. "You'll also want to avoid foods and medications that can potentially irritate your gut."

Common gut irritants to avoid before a long run include:

• Alcohol
• Caffeine
• Spicy foods
• NSAIDs, including aspirin, ibuprofen and naproxen
  
  

4. Hydrate!

There are plenty of reasons to avoid making hydration mistakes before and during a marathon — proper gut function included.

"Having less water in your body means having less water to help move food through your gut. Plus, as you become dehydrated, your body pulls water from your stomach to help maintain blood volume levels — further stressing your gut. This is why preventing runner's stomach is about more than just making good food choices, it's also about starting a race well-hydrated and maintaining your hydration status as you run," explains Lowry.

For several days leading up to the race, be sure you're drinking plenty of water and monitoring your hydration status. During the race, aim to drink between 16 to 20 ounces of fluid per hour. And be prepared to be flexible. If it's hot outside or you sweat a lot, you'll likely need more fluid than this.

"In addition, it's really important to take in fluid as you re-fuel, since fluid helps achieve both absorption and digestion of food," adds Lowry.

5. Take steps to minimize pre-race anxiety

Sometimes, you literally feel your stress in your gut. (Think: stomach butterflies). So it probably comes as no surprise that race-day anxiety can contribute to the symptoms that manifest with runner's stomach.

"The more you can minimize your stress, the better your chances of avoiding GI distress as your run. It's easier said than done, of course, but your aim should be to go into your race feeling relaxed," says Lowry. "To help calm your nerves, I recommend practicing meditation or trying to envision yourself crossing the finish line when you start feeling anxious."

Look, running a marathon is no easy feat — for your body, your mind or your stomach. But hopefully, Lowry's tips above can help you go with your gut on race day instead of work against it.