GLP1R neurons sense intestinal stretch and signal to the brain to trigger or stop eating.

“The Liberly lab, the guy's name is Steven Lieberly. He runs a lab at Harvard Medical School. They discovered a category of neurons called the GLP1R neurons. And those neurons send little wires down into the intestines and deep into the stomach, but mostly into the intestines. And they sense stretch of your intestines. And then those neurons send another branch. So they have a branch in one direction, senses what's going on in your intestines, and they have another branch that goes up from your neck into your brain to either trigger the desire to eat more or to stop eating.”