How to Experiment With and Prepare For Race Day Fueling

Ashley Lauretta
by Ashley Lauretta
Share it:
How to Experiment With and Prepare For Race Day Fueling

Surveys have found that digestive distress is common in athletes — particularly in distance runners — however, basic studies are few and far between. As many runners know, often it is all about trial and error to find foods that will work with you to not only fuel your body to perform, but also to limit gastrointestinal distress before, during and after a run. This is why it is imperative to not eat anything new before or during a run.

We talked to two experts to find out how — and when — to test whether a food agrees with your stomach so you have one less thing to worry about on the run.


When we think of digestion, usually it’s just the stomach that comes to mind. However, the whole structure is made up of 12 parts: the mouth, salivary glands, esophagus, stomach, liver, gallbladder, pancreas, large and small intestines, appendix, rectum and anus. Each plays a role in moving food and liquid through your body to get you the nutrients you need and dispose of those you don’t; the small intestine is where most of those nutrients are absorbed.

The actual process from the time you chew to the time your food is actually digested takes anywhere between 24–72 hours, explains Brandice Lardner, nutrition coach and owner of Grace Filled Plate. “If you have an upset stomach, it is likely from the food you just ate,” she explains. “However, other digestive symptoms such as gas, cramps or bloating may be from something you ate within the last 72 hours.”

With that long of a timeframe, it can be difficult to nail down what exactly is causing an upset stomach or related symptoms. As previously stated, it takes a bit of trial and error, though there is a process you can follow to see how certain foods and supplements affect your stomach specifically, especially when you’re out on a run.


One of the most recommended ways to find out if a certain food is causing problems for your digestive system is through the process of elimination. Simply put, you will eliminate the suspected foods and later reintroduce them to see if there are any issues.

“The best way to test if a certain food is causing digestive issues is to eliminate it from your diet for two weeks and then reintroduce it in small quantities,” confirms Lardner. “When doing reintroductions, be sure add only one food at a time so that you can pinpoint the cause of your digestive issues.”


This can takes time, so if you are close to an event, seeking professional help can pinpoint exactly what is causing GI distress. There are also lab tests that can help identify any allergens and your digestive health so you know if there are any previously unknown conditions that you may be up against.

“Working with a board-certified specialist in sports dietetics (CSSD) can help take away the guessing,”  says Marni Sumbal, CSSD, LDN, owner of Trimarni Coaching and Nutrition. “This will speed up the fine-tuning to help dial in pre-race and race day fueling and eating.”

There are, of course, other factors that can affect your digestive system. Lardner concludes that even adding new foods can result in anxiety that may manifest as GI distress. The digestive system alone has many moving parts and your brain can even impact your stomach.

“There could be several reasons for an upset stomach: bacteria, virus, indigestion, eating too fast, eating too much, emotional stress and even dehydration,” explains Sumbal. “As a general rule, what you eat two days before an event should be just as important as what you eat the day before.”


If you are looking to try a new breakfast or fuel to add to your running routine, Lardner advises doing so on a rest day or short run day. Your symptoms should be your guide and you may find you need to adjust the meal before the next run to fine-tune your nutrition. Lardner specifically notes this may mean changing your protein, carbohydrate and fat ratios until you have the right distribution.

About the Author

Ashley Lauretta
Ashley Lauretta

Ashley is a journalist based in Austin, Texas. She is the assistant editor at LAVA and her work appears in The Atlantic, ELLE, GOOD Sports, espnW, VICE Sports, Health, Men’s Journal, Women’s Running and more. Find her on Twitter at @ashley_lauretta.


Never Miss a Post!

Turn on MapMyRun desktop notifications and stay up to date on the latest running advice.


Click the 'Allow' Button Above


You're all set.

You’re taking control of your fitness and wellness journey, so take control of your data, too. Learn more about your rights and options. Or click here to opt-out of certain cookies.