Why Running Makes You Go

Since half marathon/marathon/spartan race season is upon us, I thought a little post on running and GI issues was in order. I think many habitual, sometimes, and “only if a bear is chasing me” runners alike probably know the feeling of having a perfectly beautiful run (or 5K test, whatever), and then BAM you gotta go. I have even heard the joke that you’re not a real runner until you’ve gone to the bathroom in public. But why does this happen?

More often than not, the source of stomach pain and bathroom breaks on a run is because of food choices, and the biggest culprit is sugar. Many runners use sugary chews, goos, or snacks to stay fueled during the run. This is smart, obviously – readily available carbohydrates at periodic times during an endurance activity will help you maintain the activity longer. So what’s the problem?

IMG_3168Osmosis is the problem. Remember from biology class that osmosis is the movement of water molecules between a semi-permeable barrier to the side with higher solute concentration so as to equalize the concentration on both sides. Your body likes to maintain a particular balance – known as homeostasis – and osmosis helps it do this. So when that high carbohydrate, low everything else fuel item of choice is digested very quickly in the stomach, it moves to the intestine. Now the intestine has a high concentration of “solute” (the sugar. Osmosis kicks in, and water is drawn into the intestine, which makes stool (that’s health professional speak for poop) looser. And I think we all know where this is going.

How Can You Fix It?

There are a few ways you can try to fix this. Of course, everyone is different, so it will likely come down to some self experimentation.

  • Avoid corn sugar. According to a blog post on constipation by Dr. Reddy, an Associate Professor of Pediatrics and Adolescent Medicine at the Western Michigan University School of Medicine, corn syrup – along with apple, pear, and prune juices – is not absorbed very well by the intestine, and have a stool loosening effect.
  • Space our your fuel – intend of eating a whole bag of chews (for some, up to 45 grams of sugar) all at once, eat 2-3 chews (or about 10-15 grams of carbs) every half hour. This will result in slower infusion of sugar to the intestine, which will avoid the large osmotic response.
  • Don’t over hydrate – it’s good to drink water, of course. But water IN the intestine is kind of the problem. So having a lot of water at once, especially with your fuel, could cause the same issue. Try to sip water throughout the run/race, aiming for about 8 -16 ounce an hour.

Image 1 c/o Vicki Wolkins

 

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