Science Explains Why That One Bad Meal Still Haunts You

The ways in which your body works to protect you without you even noticing are astonishing — and that includes your brain’s efforts to save you from food poisoning.

In early April, researchers published findings in the peer-reviewed scientific journal Nature that explored how animal brains — specifically mice — learn to associate certain flavors with sickness, even when symptoms of illness don’t appear until several hours later.

The study investigated how animal brains perform what’s known as “credit assignment,” a process that helps them determine which food or event caused them to get sick, even when the culpable meal was eaten some time ago.

It works like this: When your gut sends out a distress signal — the study calls this postingestive feedback, but it may help to think of it as a literal “gut reaction” — the brain selectively reactivates your memories of what you recently ate. This neural replay helps the brain link the thing that made you sick (i.e., the food) to the effect (i.e., puking all night long), even if they are separated by hours.

The research, led by Christopher Zimmerman and Ilana Witten from the Princeton Neuroscience Institute, uncovered this connection by tracking how mice learned to avoid certain flavors.

In the experiments, mice were offered a sip of grape Kool-Aid, followed by an injection of lithium chloride to induce gastrointestinal malaise, a more formal way of saying digestive discomfort. After just one go-around with an upset tummy, the mice developed a strong aversion to the specific Kool-Aid flavor, and when offered it again a few days later, said “no thanks” in their own little mouse way.

Interestingly, the mice did not develop the same aversion when they fell ill after consuming a flavor that they were previously familiar with. This suggests the brain flags novel experiences — or in this case, new flavors — as potentially dangerous, a behavior the scientists said is rooted in evolutionary survival.

The memory of the novel flavor and the resulting aversion were found to be stored in the amygdala, the part of the brain responsible for processing emotions, including fear and stress. Only when a flavor was new and paired with food poisoning were neurons in the amygdala reactivated during gut distress. 

While this study was performed on mice, it offers insight into how humans learn about food dangers, too. The findings suggest that our brains don’t just passively store events, but rather can actively revisit past experiences when new information (like nausea) arises. 

The study also highlights the gut-brain pathway, which further supports a growing body of research that suggests our digestive system plays a crucial role in and can impact brain function, behavior, mood, and anxiety.

The ability to “gut check” our experiences, the researchers note, is “essential for survival — nutritious foods are valuable, whereas poisonous foods can be deadly.” Even if we’re no longer at a stage in evolutionary development where we’re tasting unfamiliar ingredients that might be toxic, these learnings provide valuable information for better understanding the relationship between the gut and mind.