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The first time stomach issues ruined a long run, I thought I had food poisoning. Then it happened again. And again.

So I did what any of us would: searched the Internet for answers. Dr. Google offered some plausible explanations, from weak pelvic muscles to the gut-jarring impact of footstrikes. Running forums offered an array of solutions, from enemas for runners’ trots to dry bagels for nausea. None of this — surprise surprise — had any research behind it. (But here’s a fun fact I did learn: One quarter to one half of elite athletes have gastrointestinal distress that really cramps their style.)

Portable toilets
Portable toilets

I rang up David Nieman, PhD, director of the Human Performance Lab at Appalachian State University in North Carolina, to get his take. He explained that the main reason for runners’ upper GI problems (acid reflux, vomiting) and lower GI distress (cramping, diarrhea) is that the gut simply shuts down after a lot of exertion. “About 88 percent of blood is shunted away from the GI tract to the working muscle groups. When you shut down the blood flow, it causes high physiologic stress,” Nieman explained. “That leads to the body’s high production of stress hormones and cytokines (inflammatory proteins). You have a GI tract that reflects the stress that your body’s going through.”

He was less scientific about the ways to cope with these problems: Keep calm; eat a pre-race meal about an hour before; go easy on the fiber. But these strategies aren’t foolproof. Nieman ran 58 marathons and never figured out how to get rid of his acid reflux during races. In fact, it’s one of the reasons he gave up racing. “I would actually vomit up acid,” he said.

Research also shows that dehydration (been there) and overloading on carbs during exercise (done that) can also contribute to GI distress. Krista Austin, PhD, owner of Performance & Nutrition Coaching in San Diego (and former physiologist for the United States Olympic Committee), advises against high-glycemic carbs found in sports drinks and energy gels. “They don’t empty from the gut very well. Instead they saturate the gut with carbohydrates, and you eventually start to get that GI distress,” she said.

She recommends that all her athletes, from the slower, heavier ones to the zippy gazelles, use an easy-to-digest, low-glycemic product from Generation UCAN called SuperStarch. The advice may be worth trying, though her consulting work for the company makes it somewhat difficult to swallow.

Nieman isn’t a big fan of most sports drinks, either. In one study, he and colleagues found that sports drinks – “essentially sugar water,” he said – were no more effective than bananas when it comes to boosting athletic performance. Bananas are obviously healthier, but the research was funded by Dole Foods, which could raise questions of impartiality despite being published in the prestigious journal PLoS One.

Both Austin and Nieman tell runners to cut back on fiber before a race or long run, but Austin is more systematic about it. About three days before the race, her athletes reduce their fiber intake to about 10 grams per day by swapping brown rice for white, crunchy peanut butter for creamy, bran flakes for corn flakes, etc.

Austin has one other trick for gut-troubled runners: magnesium supplements, which can have a laxative effect at a high enough dose. “To fully empty the colon, I have some of my runners take about 800 milligrams of magnesium two nights before the race. It will help them kind of push everything out,” Austin says. Magnesium is also effective as an antacid.

Even the best training can culminate in a lousy run (or a lousy case of the runs), unfortunately. So in the event all else fails, a final word of wisdom for the newbies out there. Always race with toilet paper! Even if you don’t need it, chances are someone at that late-race port-a-john will.

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