You’re at work, in a meeting. Or maybe you’re at school. Or hanging out with friends. It’s near midday, or early evening. Suddenly you hear this low rumbling noise…and it’s coming from you.
It’s the grumbling, growling noise that your stomach makes when you’re hungry. Called borborygmi (Bor-boh-RIG-mee, the plural of borborygmus, an ancient Greek onomatopoeia…a word that sounds like the thing it describes), it has to do with peristalsis — the rhythmic muscle contractions that help push food, fluid, and gas down your gastrointestinal (GI) tract.
Your whole gut is basically a long, hollow tube that runs from mouth to anus. All along its length its walls are lined with smooth muscle (not to be confused with skeletal or cardiac muscle). These muscles’ wave-like contractions push food all the way down your esophagus through your stomach and small intestine to your large intestine.
(Courtesy the National Library of Medicine. I apologize for the horrible into and outro music.)
It’s a contractile motion not unlike that of an earthworm crawling through the dirt:
So you can think of your gut as being your inner earthworm. (Is that a good thing?)
What does this have to do with stomach noises? Everything. A couple of hours after a meal, the walls of your stomach sense the absence of food and trigger the release of hormones that signal to the brain, “I’m empty!”
In response, the brain tells the muscles in the lower part of your stomach (the antrum) and the small intestine to start contracting as a way of priming the pump, getting everything ready to start moving food again. Those contractions radiate down the length of the small intestine (on average, 22-1/2 feet in men and 23-1/3 feet in women) to the large intestine, sweeping everything clear and releasing acids and digestive juices. They’ll run for about 10 or 20 minutes, and then subside for another couple of hours.
Along the way, those priming contractions also move gas around in the intestines — and it’s the gas moving around that makes noise.
“But I just ate!” you exclaim. “Why would I be producing peristaltic borborygmi now?”
(I dare you to say that in a crowded room.)
Your stomach growls when you’re not hungry precisely because you just ate. Now you’re full, and that food you’re digesting has to go somewhere. Peristalsis is doing it’s job — moving the slurry of digested food and fluids (called chyme) out of your stomach and down through your small intestines, where the nutrients will be absorbed. And it’s moving gases from the digestion process through your intestines too, again causing borborygmi.
The vast majority of the time borborygmi are totally normal, though rarely they can signal the presence of intestinal blockage or GI diseases like celiac disease or inflammatory bowel disorder.
And we’re not the only species to get the rumbles. Many animals do too, including cats and dogs, cows and sheep, horses, rabbits, and rodents. For veterinarians, GI noises can be an important diagnostic tool for GI concerns like colic and bloat.
If you want to learn more details about the interplay of hormones and electrical signals that cause peristalsis and, in turn, borborygmi, check out this brief explainer on Scientific American.
Now if you’ll excuse me, my borborygmi just reminded me that it’s time for breakfast.