Ask Stacy

Leading sports nutritionist and exercise physiologist Dr. Stacy Sims answers your most pressing questions.

How can we combat GI issues in the heat?

Racing in the heat presents challenges, and as the intensity and/or duration increases, there is a significant impact on gut permeability—or how easily substances like nutrition and hydration pass through the gut into the bloodstream. Also, it’ s important to remember that racing in the heat increases stressors like ischemia and positional changes, which causes many GI issues. Not to mention dehydration (which further increases gut permeability). All well and good to know this, but what do you do when you are in the middle of a big race and your stomach starts to roil and all you can think of is not vomiting (or worse)?

First and foremost, slow down. Yes, it is a race, but the goal is to get to the finish line! By slowing down you ’ll do more than just reduce your heart rate, you will also reduce the amount of heat your body is producing (from the working muscles), which will help redistribute some of your blood to the gut. This reperfusion will increase oxygen to the intestinal cells and help reduce the permeability of your intestinal cells.

Next, try to find cool water—not the stuff that has been sitting in the sun for a while—and even chew some ice if possible. This will help reduce the heat load in the digestive tract; again, helping to reduce the ongoing injury to the intestinal barrier. On the other hand, warm fluids speed up gastric emptying—something you definitely don ’t want.

Eat something bland (crackers, pretzels), and stay away from gels, other concentrated liquid carbohydrates, salt tablets, and caffeine—all which have been shown to promote GI permeability and disrupt fluid balance of the gut, even though your instincts may tell you to reach for any or all of them. If possible, look for an amino acid-based solution that contains glutamine and L-arginine. These two amino acids have specific actions to prevent increased intestinal permeability and slow down the

“Over-the-counter medications might seem to be an answer to mid-race woes, but they ’ re not! NSAIDs (non-steroidal anti-inflammatory drugs) increase irritation to the stomach. ”

rate of heat-induced damage to the gut.

Over-the-counter medications might seem to be an answer to mid-race woes, but they ’ re not! NSAIDs (non-steroidal anti-inflammatory drugs) increase irritation to the stomach. Even more counterintuitively, Imodium is designed to slow gut motility in resting conditions, but it should not be used in high-stress, high-sweat, and/or long-duration exercise, as its primary function is to slow gut motility by altering water and electrolyte balance. There is also an increased risk of heart-rhythm disruption due to dehydration, coupled with lower blood levels of magnesium and potassium.

Like all things, prevention and preparation are your best ammunition against race-ending GI problems. Be heat adapted before your race; this can be from spa or sauna time, after workouts, leading up to your race, or small, short intensity sessions in the middle of the day in the heat—anything to invoke heat stress to allow your body to adapt and adjust. Nutritionally, supplementing with glutamine (0.9g/kg of body weight) two hours before exercise can decrease intestinal permeability and improve the integrity of the protective lining of the gut. Focus on hydration and avoid foods that are high in fiber or fat or contain known irritants (fructose, sugar alcohols, spices) in the 24 hours leading into your race.