Q. Why does your stomach growl?

Medford

A. Several times a day your gastrointestinal system, triggered by the hypothalamus in the brain, turns on and off. Eating turns it on.

Even seeing something you want to eat can get things going. But at other times, even when you are sound asleep, your autonomic nervous system is turning your gastrointestinal tract on and off, so it can work on its four basic jobs: digestion (dissolving and breaking down food), secretion (squirting out enzymes to help break down the food), absorption (sending the molecules produced by digestion into your bloodstream so the body can use them), and motility (moving things through the system from one end to the other. Those processes take hours.

In the active state, the stomach muscles contract more frequently and more powerfully. That causes things in there, whether solid food, liquid, or even air taken in when you swallow, to move around. The movement produces vibrations we hear as growling, or rumbling, or gurgling.

Some people associate a growl with hunger. According to Dr. Barbara Nath, a gastroenterologist at Massachusetts General Hospital, that could be because we hear the growling sound when the digestive system is active but the stomach is empty, making us think the growl is caused by the hunger.

Or it could be because during a meal, the stomach is going through various contractions as it sorts through its contents, sending liquids and small particles on to the small intestines but larger particles back up into the stomach for further digestive breakdown by gastric acids.

But it's myth that the growl is caused by air in an empty stomach. Dr. Steven Shields, a gastroenterologist at Brigham and Women's Hospital, says, ``We couldn't tell with a stethoscope whether you're hungry or full. The noises only tell us whether the intestinal tract is awake or asleep.''