Unless you have ironclad guts, there’s a good chance you’ve thrown up thanks to running. Because vomiting is an unpleasant occurrence that doesn’t discriminate, knowing its possible causes is essential if you want to avoid regurgitating after (or during) a tough run.

If you’ve ever found yourself draped over a bin after picking up your race medal, here are some possible reasons for your gut’s dissatisfaction – and the ways you can try combating it.

1. A digestive system shutdown

When you’re running, oxygen-rich blood is directed away from the stomach and other nonessential organs and sent to your lungs, heart, and other working muscles that need it more during high-intensity efforts. Because your stomach doesn’t have the normal resources to digest nutrients as efficiently as usual, this might be why you vomit after a run, especially if you consume too much fuel while running or too soon after you finish.

Running while it’s hot and humid outside also produces the same result because blood flow is redirected to the skin as a means to cool down the body.

To avoid it, practise fuelling during training runs to dial in on how much fuel your stomach can handle on race day, says Carwyn Sharp, an exercise physiologist and sports nutritionist. And if you’re consuming energy gels or other sugary foods, try to ingest them with water to aid in digestion. Even when you’re not working out, simple sugar is hard to break down, so downing too much sports drink or gels all at once could spell trouble.

Dehydration also slows the digestion process even more, so sipping water early and often is important to help you digest food better. “Hydration is key to maintaining a healthy GI and avoiding nausea, but it’s a balancing act to hydrate enough to avoid nausea but not too much so as to cause it,” says Sharp.

2. Increased pressure on the stomach

“When you run at a high intensity, you increase the pressure in the intra-abdominal space, which puts pressure on your stomach,” Sharp says. This occurs because you use your core more and take heavier breaths while you’re running. When this happens, it can force contents in your stomach back up into your oesophagus – possibly all the way back up to where it started.

This scenario is more likely if you had a large quantity of food or liquid in your stomach before a run. This amount is highly individualised, however, so determining what your body can tolerate is essential, especially going into a race.

“The more food you have in your stomach during an intense race or workout, the higher your risk of vomiting,” Sharp says.

Some runners might face a disorder called gastroesophageal reflux disease (GERD) and are at an increased risk of experiencing this scenario. That’s because their lower oesophageal sphincter – the mucles between the oesophagus and the stomach – are weakened and may relax when they are not supposed to.

GERD can be treated with medications or an adjustment in diet away from foods that can irritate the oesophageal lining, such as acidic foods, tomato products, fatty foods, alcohol and coffee, Sharp says.

3. Consuming the wrong foods and beverages beforehand

Steer clear of highly acidic foods like citrus fruits (oranges, berries, grapefruits), processed cheeses, as well as liquids like soda or orange juice before your run.

“Acidic foods and beverages cause the stomach environment to be more acidic,” Sharp says, “which slows emptying of the stomach contents into the small intestine, but also increases risk of vomiting.”

High-fat, high-protein or high-fibre meals and snacks are a no-no before a workout as well because they slow down the gastric emptying process. In other words, the food stays in your stomach longer, and it might still be present during your run and give you that “brick in the belly feeling” that’s hard to keep down.

To keep food-induced vomiting at bay, try not to eat during the two-hour window before a hard workout or race. “If you do need to eat something, make it bland and small in volume,” Sharp says.

If diet adjustments don’t work, take antacids about an hour before running to reduce nausea and vomiting.

4. Stopping too quickly

Hitting the brakes hard after your last interval or once you’ve crossed the finish line can wreak havoc on your stomach because it’s not prepared for the rapid change in exertion, causing you to feel ill as you return to normal. (It’s similar to how you might feel after riding a wild roller coaster.) This can be exacerbated if you really push hard during the final stretch, Sharp says.

Rather than dropping to the curb, try to keep walking or jogging to give your body time to readjust and ward off stomach cramping. Also, resist chugging a sports drink or downing food too quickly. Sip on water, keep walking, and allow your body to return to stasis level.

5. Excessive dehydration

According to our Sports Doc, William Roberts, M.D., you might be getting nauseated if you’re an especially heavy sweater. If you lose more than four per cent of your body weight while running, some studies say your gut quits absorbing liquids correctly, which causes queasiness.

“This is especially true for those who are dehydrated before they start to replace fluids during exercise,” he says.

For those who believe spilling your guts is a sign of a race well run, it’s not. Vomiting can cause damage to the lining of your esophagus, which can affect digestion.

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