A study found that fly larvae have special sensors, or receptors, in their esophagus that trigger as soon as they swallow something, prompting the brain to release serotonin and making the larvae continue eating. Researchers believe humans have a very similar control circuit too

>This process enabled the researchers to identify a sort of “stretch receptor” in the esophagus. It is wired to a group of six neurons in the larva’s brain that are able to produce serotonin. This neuromodulator is also sometimes called the “feel-good hormone.” It ensures, for example, that we feel rewarded for certain actions and are encouraged to continue doing them.
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>The serotonin neurons receive additional information about what the animal has just swallowed. “They can detect whether it is food or not and also evaluate its quality,” explains the lead author of the study Dr. Andreas Schoofs. **“They only produce serotonin if good quality food is detected, which in turn ensures that the larva continues to eat.”**
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>**This mechanism is of such fundamental importance that it probably also exists in humans. If it is defective, it could potentially cause eating disorders such as anorexia or binge eating**. It may therefore be possible that the results of this basic research could also have implications for the treatment of such disorders. “But we don’t know enough at this stage about how the control circuit in humans actually works,” says Pankratz to dampen any overly high expectations. “There is still years of research required in this area.” 

Paper: [Serotonergic modulation of swallowing in a complete fly vagus nerve connectome – ScienceDirect](https://www.sciencedirect.com/science/article/pii/S0960982224011370?via%3Dihub)