When you haven't eaten in a while, your body has ways of reminding you that it needs fuel. Often, the stomach nudges you toward your next meal by making loud gurgling noises. But why, exactly, do our stomachs growl?
"Stomach growling is due to peristalsis," Tiffany Weir, professor of food science and human nutrition at Colorado State University, told Live Science.
Peristalsis is a series of wavelike muscular contractions that propel gas, food and liquids along the hollow tube of the digestive tract. The human digestive tract, which includes the mouth, esophagus, stomach, intestines and rectum, is essentially a long, muscular pipe. To get food from one end to the other, the muscles built into the lining of this tube contract in a sequence, one set of muscles after another, which pushes digestive contents along.
Stomach growling, or borborygmi, is the sound caused by these muscle contractions, and they don't just happen when you are hungry.
"Your stomach can growl when it's hungry or when it's full because we have hormones that regulate our appetite and trigger peristalsis," Weir said. Immediately after a meal, there is a lot of peristalsis going on. There are an average of three waves per minute in the stomach and 12 along the small intestine. As food is pushed through the digestive tract, it is mixed and churned for easier digestion, and the mixing of solids and liquids during digestion is not a silent process.
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This peristaltic action often goes unnoticed because the contents of the stomach and intestines muffle any sound the digestive tract may make. But an empty digestive tract is much noisier, which may explain why stomach growling is noticeable when someone is hungry, making it commonly associated with hunger..
According to the National Institutes of Health, when the stomach has been empty for a few hours, it begins to secrete a hormone called ghrelin. When this hormone reaches the brain, it triggers feelings of hunger and stimulates peristalsis in the digestive tract.
The reason the stomach and intestines might contract in the absence of food may be to clear out any excess liquid, solid or microbial debris that may be lingering in the stomach or intestines, Mark A. W. Andrews, a professor of physiology and associate director of the Independent Study program at the Lake Erie College of Osteopathic Medicine in Pennsylvania, said in an article for Scientific American.
This peristalsis is much slower than when the digestive tract is full, as it only occurs about once every 20 minutes. However, because there is more air than solid material in the tract, loud rumblings can often be heard when the digestive tract is empty.
Sometimes, stomach growling and gurgling is caused by digestive problems. Incomplete digestion of certain foods, like plant material, such as beans, and dairy products, can produce excess gas that amplifies the sounds of peristalsis. Digestive illnesses like gastroenteritis can cause diarrhea, which involves increased peristaltic action in an attempt to clear the intestines, which can also be quite noisy.
Illnesses aside, stomach rumbling is a common and harmless side effect of the way the human digestive system operates.
This article is for informational purposes only, and is not meant to offer medical advice.
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Cameron Duke is a contributing writer for Live Science who mainly covers life sciences. He also writes for New Scientist as well as MinuteEarth and Discovery's Curiosity Daily Podcast. He holds a master's degree in animal behavior from Western Carolina University and is an adjunct instructor at the University of Northern Colorado, teaching biology.