GI issues while running
Nutrition and Diet, Sport Nutrition

How to Stop GI Issues From Hurting Your Running

GI issues while running- more common than you might think!

Did you know an estimated 70% of runners have experienced GI issues or ‘tummy troubles’ while training or competing?

70-f******* percent!

While ‘runner’s diarrhea’ is generally thought to be the “worst” symptom to experience, GI symptoms during exercise can include nausea, vomiting, cramps, bloating, or burping. For some of us symptoms are relatively minor, or only occur if we know we messed up (like if I were to say, eat a cheeseburger and fries before heading out for a run!). For other runners, GI symptoms can be mysterious, frustrating, and debilitating. They can also affect runners at all levels, from newbies to elites. So, if you struggle with GI issues during running, you’re not alone!

In this article I’m breaking down the various causes of GI distress while running, from top right to er, bottom. I’ll also be sharing my tips and strategies on how to train your gut to avoid these annoying and performance killing symptoms!

Wait, You can train your gut?

Yes, you can! We all understand the importance of training our muscles and cardiovascular system to become better runners. But, you can also train your gut! Training your gut can help you tolerate pre-workout food and fluids better, which in turn can have a dramatic impact on your running performance. If you’ve ever experienced gastrointestinal problems like nausea, bloating, cramps, or diarrhea during a training session or competition you might be relieved to find out there is a solution!

Most athletes can recall a situation where “tummy trouble” interfered with a workout or competition. This is no surprise since research shows that the vast majority of athletes in many different sports have encountered GI symptoms at some point in their career. GI distress can impact a runner at any stage of training, from an easy long run to some high-intensity speed work. But, high-stress events can dramatically increase your chance of developing a sensitive stomach- like during a big race!

I can personally think of a few situations where I’ve found myself in a bit of a…situation while out on a run. Don’t worry, I won’t share the details here! But because ‘bathroom’ talk can be embarrassing and a bit taboo, many people suffer in silence. And I’m here to help fix that!

What are the causes of GI Issues during exercise?

The GI tract is a 30-foot (NINE meter!) long tube that is working 24/7. It’s in constant motion- digesting and absorbing nutrients from the food we eat. Even in between meals the GI tract has a ‘flow’ of movement that keeps things heading in the… right direction. Fluid, electrolytes, vitamins, minerals, fats, amino acids, carbs are all finding their way to the right spot where they can leave the GI tract and enter our body. There’s a lot going on, and it’s pretty amazing. When it works well that is!

Does anyone remember the Magic School Bus episode on digestion? Check it out for a quick refresher!

GI issues can be frustrating and challenging, because we can’t just LOOK inside someone to see what’s going on. But, here are some common things that might be your problem!

It could be your pre-workout meal

You can probably guess that food and beverage choices before and during exercise can play a major role in how our gut functions once we start moving. But, other physiological factors can contribute too!

After eating and while we’re at rest, a significant amount of our body’s blood flow is concentrated around the GI tract. This is to help our body digest our food and carry the nutrients we absorb from our meal to the rest of our body’s cells. We call this phase “rest and digest”

When we begin exercising (running for example) blood flow around the GI tract is reduced because it’s needed to help bring oxygen to our working muscles. This redirection of blood flow can slow down our digestive processes, leaving food sitting in the GI tract for longer than we’d prefer. From an evolutionary perspective we typically call this phase “fight or flight”. The difference is our ancestors didn’t just run for fun. They were usually running after their next meal, or from something to not become it’s next meal!

This issue of impaired digestion can contribute to a range of symptoms including diarrhea, nausea/vomiting, cramps, bloating, and abdominal pain. Read on to find out what you can do about it!

Better pre-training food choices to prevent GI issues

So, how might we adapt our pre-training nutrition strategy to promote faster digestion? What can we eat so there isn’t still food in our gut when we head out the door? Unfortunately, many runners will opt to simply skip their pre-training nutrition in order to avoid GI symptoms. But, without adequate fuel we’re more likely to wind up hitting the wall than crushing our PRs. We’ll struggle with the power we need to actually run faster and complete more intense workouts.

What we want pre-training then is to focus on high carb foods that are lower in fat and protein. We also want them to be not too high in fibre. This is because fat, protein, and fibre (wonderful as they are) take longer to leave our stomach and be digested and absorbed. These nutrients are great for keeping us full for longer after a meal, but can mean debilitating symptoms for athletes.

Higher carbohydrate food choices might mean:

  • breakfast cereal
  • toast with a small amount of peanut butter and jam
  • oatmeal
  • fruit or fruit juice
  • sports drinks

Follow me on Instagram for more pre-workout meal ideas!

Does the type of carbohydrate matter?

For some runners, yes it can! Some runners have difficulty digesting certain types of sugars, which can cause them significant GI distress while running. Similar to the protein and fat problem, these sugars can remain in the GI tract undigested and unabsorbed after eating. These sugars then actually draw water INTO the gut. Typically, water should be leaving the gut during this phase of digestion. This increase in water causes everything to start moving much more quickly through our digestive tract, causing us to run to the bathroom!

Lactose and fructose are the two primary sugars that can be the source of many runner’s woes.

  • Lactose is the sugar found in milk (you might be familiar with this one, as it’s common for people to be lactose intolerant)
  • Fructose on the other hand is an issue primarily when it is found in high amounts in a food. These can range to some fruits (very ripe bananas, apples, cherries, mango, peaches, raisins, or watermelon) to natural sweeteners like honey. You may need to examine the fruits you consume pre-training, or swap out the honey-containing energy gels.

It could be dehydration

Our hydration status can also play a key role in how our gut functions during exercise. The volume of blood we have in our body is related to how hydrated we are. When we’re running we’re sweating (probably), and losing water via our sweat.

When our blood volume drops a few body systems can start to struggle. For example we’ll have a harder time regulating our body temperature and can start to overheat. We may also have an increase in heart rate, because there is less blood to pump around our body. Finally, this drop in blood volume can also limit the blood flow around the GI tract, triggering symptoms. Nausea or cramps tend to be the most common symptoms triggered by dehydration.

Staying hydrated is the key to prevent these issues, but that can be tough. Especially during long running events or on hot/humid days. We also want to choose the best beverage for our needs, which may not always be plain water!

The problem with plain water

As you’ve probably gathered by now, the name of the game in preventing GI issues is to avoid things hanging around in our stomach for longer than they need to. Interestingly, plain water actually leaves the stomach more slowly than fluids that contain a small amount of salt and/or sugar. Carbohydrate and electrolyte-containing fluids also do a better job of keeping us hydrated during prolonged exercise. They keep more fluid in the body where it’s needed, vs being removed by our kidneys and peed out. To make things even more complicated, beverages that have too much salt and sugar can also lead to delayed stomach emptying and GI distress. Getting the right balance is the key!

How much salt or sugar is needed to optimize the rate of stomach emptying? About the same concentration as our blood actually! It’s easier for us to absorb fluids that are similar in concentration to our bloodstream. We would refer to these as being ‘isotonic’.

Sports drinks for example, are formulated to have the right amount of sugar and electrolytes to maximize absorption.

Drink isotonic fluids during exercise.

Fluids with a small amount of carbohydrate and sodium (like a sports drink) are more readily absorbed during exercise. These do a better job of keeping us hydrated during prolonged exercise than plain water. You also want to plan your hydration strategy! Drink small amounts every 10-15 minutes rather than chugging a large amount all at once. This will also help to reduce potential GI issues like cramps, nausea, or diarrhea.

Read more about whether sports drinks or water are the best choice for you here!


It could be stress or anxiety

Ever had the pre-race jitters? That little bit of nerves we feel as we stand at the start line can have a big impact on our gut. But, this isn’t just an issue on race day for many runners.

Stress or anxiety at any point in time can alter our gut motility by way of the gut-brain-axis. You might experience diarrhea, constipation, bloating, gas, or abdominal pain. While taking steps to reduce stress and anxiety can reduce the frequency or severity of these symptoms, unfortunately living a stress-free life isn’t possible for most of us! Awareness of these factors though is a step in the right direction. Practice some mindfulness techniques, incorporate deep breathing, and create a calming pre-race routine to keep the jitters at bay.


One final tip: be careful with caffeine

Caffeine is a stimulant and it can increases the speed at which food moves through the GI tract, which increases the speed at which we need a toilet. Even if you follow all of the above strategies, too much caffeine before a workout can trigger anxiety, nausea, cramping, and diarrhea. This is especially true with higher doses of caffeine. For athletes, most research studies recommend a pre-workout dose between 3 and 6 mg per kilogram of your body weight. More than that can mean trouble, and won’t enhance your performance.

Check the labels on any pre-workout supplements you take for their caffeine content. Don’t forget to include any pre-workout coffee or tea. The exact amount of caffeine in your favorite hot beverage can vary, but is somewhere between 60-120mg per cup.

For more on which pre-workout supplements are worthwhile, click here!

Curious if caffeine will actually help your athletic performance? It isn’t right for everyone. Read more here!


When to see a Doctor

In some cases, these GI symptoms I mentioned above are signs of a larger medical issue. If your issues don’t resolve with any of my suggestions in this post, or if you’re worried about the symptoms that you’re having, please book an appointment with your family doctor for some further testing.


The bottom line

GI issues are a common problem amongst runners, but it doesn’t have to be that way! A little nutrition strategy, and learning to choose the right foods and beverages before training can dramatically reduce the frequency and severity of common GI problems. Additionally, over time our gut becomes much better at handling our pre-training meal. So, just like you need to practice running to get better at it, you can practice training your gut too!


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About the Author: Stephanie Hnatiuk is a Registered Dietitian, Personal Trainer, and Diabetes Educator. She specializes in sport nutrition strategies for runners of all levels, and loves helping fellow runners cross the finish line faster!

Are you looking for a little more one on one help with your nutrition and training as a runner? Click here for more information about my one on one coaching program!

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