Ask A Scientist

How does our stomach know when to rumble?

Asked by: Christopher Heimes
School: Maine Endwell Middle School
Grade: 6
Teacher: Kevin Wagstaff
Hobbies/Interests: I like to play sports and swim.
Career Interest: Sports announcer or basketball player in the NBA.

Answer from Lina Begdache

PhD candidate, Binghamton University

Research area:
Nutrition and obesity, cell and molecular biology, neuroscience.

Interests/hobbies:
Tae Kwon Do, basketball, jogging and visual art.

If I was to record down my very first thought, I would say: the stomach rumbles always at the wrong time! This is when we are most aware of it; when all is quiet and we are working hard on building that good impression around us! As much as stomach rumblings could be embarrassing, they are signs of healthy gut when they come pain-free. Although these growling sounds are psychologically associated with hunger, the latter is not the direct cause of the stomach rumbling or borborygmus (the medical term for rumbling). Let's explore briefly together the digestive tract and the path of the ingested food to pinpoint where in this process rumbling occurs. A healthy digestive system, which is a hollow tube from mouth to anus, is lined with muscles that cause continual contractions in order to push all foods, digestive juices and mucus down the tube towards the anus a few inches at a time. The squeezing of the muscular walls is termed peristalsis which is under the autonomic nervous system (that controls involuntary functions) and hormonal control. Mechanical distension of the stomach by swallowed food triggers the autonomic nervous system to take action. Digestive juices are secreted and food starts to propel through the intestines. This sets off a reflex to empty the intestines before the upcoming of the digested foodstuff. That explains why people visit restrooms following an ingested meal. The whole process of food digestion/propulsion is carried by the rhythmic contractions of the gastrointestinal wall. However, rumbles are inaudible as they are muffled by the presence of food. Between meals, contractions continue to clear mucus, bacteria and all remaining food particles through the intestines to prevent unnecessary accumulation in a particular spot. As the stomach and intestines empty, the contractions start to vibrate in the hollow space and produce what is called 'rumbling'. When they become particularly strong, they can fuse together to produce a sustained contraction which is usually that embarrassing sound that turns most people faces red. Those contractions are most intense in children and young adults with a higher degree of muscle tone. In addition, it is believed that the contraction of the intestinal wall increases following a slight drop in blood sugar, which basically occurs about 2-3 hours after the last ingested meal. It is worth mentioning that too much rumbling could be an indication of excessive gas produced secondary to undigested food components like lactose. An absence of bowel sounds could be due to intestinal obstruction. So, the next time your stomach rumbles, smile for the reason that you have a healthy gut!

Last Updated: 9/18/13