Many of us have experienced GI <gastrointestinal> issues on long runs or race day. GI issues can be in the form of nausea, sloshy stomach, vomiting, cramping, or diarrhea. Let’s take a look at what can cause it & what we can do to prevent it.


Often, dehydration is the cause of GI distress during long runs or on race day. When you are dehydrated, there is less blood flow to your GI tract, and thus, your body cannot digest and absorb nutrition & fluid as efficiently.

To avoid GI distress caused by dehydration, make sure you hydrate well the entire day before a long run or during your carb load leading up to your race. Hydrate the morning of the run with electrolytes and take in enough fluid & sodium during your run. If you are a heavy/salty sweater or it is warmer outside than you prefer, consider hyperhydrating the night before a long run or race.  <To read more on hydration needs, check out our Hydration page>.


Some of us have stomachs of steel and can eat whatever we want leading up to a long run or race. But, for those of us who don’t, too much ‘roughage’ the day before leaves a little too much ‘behind’ to cause problems the next day during the run. Take a look at what we are eating the night before and the morning of your run/race. Focus on getting in simple carbs and limiting fat and fiber, which may cause GI distress. Those with sensitive stomachs may need to skip the salads and veggies the night before those long runs and races. Simple carbs include: white bread, pastas, rice, bagels and crackers, fruit juices, sports drinks, etc.

Liquid & Gel Concentration

If you dump too much sugar from gels and hydration drinks in your stomach at one time or you aren’t used to taking nutrition during your runs, it may cause GI distress. Be sure to mix your hydration drinks according to the directions so they aren’t too concentrated. And, train your gut to take gels during your long runs <use our calculator to determine your needs>. You may need to play around with different types of drinks and gels to find what works best for you.

Core Body Temperature

When your core body temperature increases, gastric emptying decreases, and so does the absorption of nutrition. Hydration is one of the keys to this – so make sure you are well-hydrated going into your run & stay on top of your hydration during the run. Try to stay as cool as you can – wear the right clothing, find some shade when possible, cool off in a sprinkler – whatever gets the job done.


As your rate of perceived exertion (RPE) increases, your ability to absorb nutrition and fluid decreases. This is a big reason why I always say ‘Fuel Early & Often’ – If we fuel early & often while we are feeling good before our RPE gets too high, we will have a little wiggle room at the end if we cannot tolerate fuel at that time. And during a race, we will have more fuel stored from our carb load to fall back on.

If you need help to figure out why you are experiencing GI issues during your runs, Meghann can help! Complete a coaching application for a Last Minute Crunch Time Session with Meghann.

Disclaimer: The content in our blog articles provides generalized nutrition guidance. The information above may not apply to everyone. For personalized recommendations, please reach out to your sports dietitian. Individuals who may chose to implement nutrition changes agree that Featherstone Nutrition is not responsible for any injury, damage or loss related to those changes or participation.