Mankind has been puzzling over the rumbling in our stomachs for so long that even the ancient Greeks came up with a name for it: borborygmi. The word attempts to put the sound of the grumble to mouth.
The real deal is strange and sometimes embarrassing, so we decided to get to the bottom of it. What is it that makes our stomachs shout out?
Hunger is certainly a factor. When you haven't chowed down in a two hours, receptors in the walls of your stomach trigger the hunger-arousing hormone ghrelin, which tattles to your brain that the pipe is empty. There are other things, like low blood sugar, that also send that message. And your brain, being the boss, steps in to solve that problem by releasing the hormone orexin, which tells your stomach it might be time to fill ‘er up again.
It's the hypothalamus, which is in charge of body maintenance functions like controlling hunger, body temperature and your sex drive, that gets the credit for "switching on" that get me a hamburger feeling. It happens in stages.
First the hormone triggers your stomach's smooth muscles to contract. Acids and other digestive fluids are deployed in the stomach and intestines to get the space ready for the next meal. The contractions move in a ring-shaped formation along your entire gut, forcing remaining mucus, food and bacteria from the area. These contractions produce vibrations, which are responsible for making the racket. The grumblings can last up to 20 minutes and repeat every hour or two until you've gotten food in your belly.
But the noises don't only occur when you need food, although they're louder in an empty cave; they happen after you've eaten, too. The contracting muscles of your stomach and small intestine are also responsible for mixing food with gas and fluid. These contractions move down the intestinal tract toward the exit just a few inches at a time. All this food/gas/liquid squishing also makes your stomach muscles vibrate, which produces a more tempered rattle.
Bad news is, there's no way to tell it to simmer down. Hungry or not hungry, you're going to have to put up with your stomach's ruckus.