Swallowing makes the brain happy — revealing surprising trigger for overeating

BONN, Germany — Have you ever wondered why it’s so hard to stop eating after just one slice of pizza or one potato chip? Scientists may have found the answer, and it lies in a surprising place: your throat.

A new study from researchers at the University of Bonn in Germany and the University of Cambridge in the United Kingdom has uncovered a fascinating control circuit in our bodies that plays a crucial role in why many people love to eat. While the enticing aroma and delicious taste of food might kickstart our meal, it turns out that the pleasurable sensation of swallowing is what keeps us coming back for more.

The key player in this dietary drama is serotonin, often dubbed the “feel-good hormone.” When we eat something tasty, our brain releases serotonin, creating a sense of pleasure and reward that encourages us to keep eating. But how does our brain know when to release this chemical cheerleader?

That’s where the new discovery published in the journal Current Biology comes in. Researchers found special sensors in the esophagus – the tube that carries food from your mouth to your stomach – that act like tiny food critics. These sensors are triggered as soon as we swallow, sending a message to the brain about what we’ve just eaten.

Now, you might be wondering how scientists figured this out without peering down the throats of people. The answer lies in an unlikely lab assistant: fruit fly larvae. These tiny creatures, with their relatively simple nervous systems of just 10,000 to 15,000 nerve cells (compared to our 100 billion), provided the perfect model for studying this complex process.

“They can detect whether it is food or not and also evaluate its quality,” explains Dr. Andreas Schoofs, the lead author of the study, in a media release. “They only produce serotonin if good quality food is detected, which in turn ensures that the larva continues to eat.”

The research team, led by Professor Michael Pankratz from the University of Bonn, embarked on a painstaking journey to map out the entire nervous system of these larvae. They sliced a single larva into thousands of ultra-thin sections, photographed each one under an electron microscope, and used a supercomputer to create a 3D model of its nervous system.

“We wanted to gain a detailed understanding of how the digestive system communicates with the brain when consuming food,” says Pankratz. “In order to do this, we had to understand which neurons are involved in this flow of information and how they are triggered.”

This meticulous work allowed the team to identify a “stretch receptor” in the esophagus connected to a group of six neurons in the larva’s brain capable of producing serotonin. When the larva swallows food, these neurons spring into action, releasing serotonin and encouraging continued eating.

While the study focused on fruit fly larvae, the researchers believe this mechanism is so fundamental that it likely exists in humans as well. This discovery could have far-reaching implications for our understanding of eating disorders such as anorexia or binge eating.

“We don’t know enough at this stage about how the control circuit in humans actually works,” Pankratz cautions. “There is still years of research required in this area.”

Nevertheless, this research opens up exciting new avenues for exploring the complex relationship between our digestive system and our brain. It suggests that the act of swallowing itself plays a crucial role in eating, beyond just getting food into our stomachs.

So, the next time you find yourself reaching for that extra slice of pizza, remember: it might not just be your taste buds talking. It may be that the act of swallowing is what’s actually making you feel good.