The rumbling or gurgling sounds that come from the abdomen are medically known as borborygmi, which is the sound of the digestive system actively working. Most people associate this noise with an empty stomach demanding food, yet the sounds often occur even when a meal was recently consumed. Borborygmi is a result of several different biological mechanisms that involve the movement of gas and fluids within the gastrointestinal tract. Understanding these mechanisms reveals why the stomach can be noisy regardless of whether a person is hungry or not.
The Sound’s Origin
The digestive system is essentially a long, muscular tube, and the noise we hear is purely a result of movement within this hollow space. The walls of the stomach and intestines are lined with smooth muscle that contracts and relaxes in a wave-like motion called peristalsis. This process is necessary to propel food, digestive juices, and waste along the tract.
The characteristic rumbling sound is generated when pockets of gas and liquid are squeezed through the narrow pathways of the intestines by these muscular contractions. When the digestive tract is full of food, the contents act as a natural muffler, which dampens the sound. However, when the tract is mostly empty, the same movements cause the sound to echo and become loud enough to be heard clearly outside the body.
When Hunger is the Cause
The most familiar cause of borborygmi is the body’s hormonal response to a need for energy. When the stomach has been empty for a few hours, specialized cells in the gut begin to release a hormone called ghrelin. Ghrelin, often termed the “hunger hormone,” signals to the brain that it is time to eat, and it also has a direct effect on the digestive muscles.
The hormone stimulates the muscles of the stomach and small intestine to contract forcefully. These contractions prepare the digestive environment for the incoming meal by clearing out any remaining contents. This active, hunger-driven peristalsis moves the air and fluids in the empty stomach, creating the loud, recognizable growl interpreted as a request for food.
The Migrating Motor Complex
The primary reason for growling when a person is not hungry is an entirely different process known as the Migrating Motor Complex (MMC). This is the digestive system’s self-cleaning cycle, which routinely sweeps the small intestine free of debris. The MMC begins about 90 minutes after the last meal has been processed, functioning purely in a fasting state.
The purpose of the MMC is to ensure the small intestine remains clean, preventing the buildup of residual food particles, mucus, and bacteria. If the small intestine is not regularly cleaned, bacteria can migrate upward from the large intestine. The cycle involves intense, rapid contractions that travel the entire length of the small bowel.
These strong, sweeping contractions are responsible for the loud noises heard hours after eating because they occur in an empty environment. The movement of the powerful wave through a tract filled only with air and digestive fluids amplifies the sound considerably. Any new food intake immediately interrupts the MMC, pausing the cleaning cycle until the fasting period has been re-established.
Other Common Triggers and Minimizing the Noise
Borborygmi can also be triggered by factors unrelated to either hunger or the cleaning cycle, primarily involving the introduction of excess gas into the system. Swallowing too much air, a phenomenon called aerophagia, is a common culprit. This can occur when drinking carbonated beverages, chewing gum, or eating and drinking too quickly.
Certain foods can also cause pronounced gut noise due to the gas produced during their breakdown by gut bacteria. Foods high in fermentable carbohydrates, such as beans, lentils, and cruciferous vegetables, lead to increased gas production in the intestines. Additionally, sugar alcohols and artificial sweeteners like sorbitol and fructose can be poorly absorbed, leading to excess fluid and gas in the digestive tract.
Minimizing the Noise
To minimize loud abdominal noises, people can take simple steps based on these triggers. Eating slowly and chewing food thoroughly reduces the amount of air swallowed with each bite. Avoiding carbonated drinks and chewing gum can decrease the volume of gas entering the system. Drinking a small amount of water when a growl begins can help quiet the noise by providing a fluid to mix with the gas, which muffles the sound.