Researchers at the University of Bonn have identified fat cells in the head as a key player in how fruit flies learn to avoid spoiled food after a single lousy experience.
The study, published in Neuron, shows that when bacteria from spoiled food enter the fly’s body, the immune system detects them and sends signals to nerve cells near the throat.
These nerve cells relay the information to a fat depot in the head, where they trigger the release of octopamine — a neurotransmitter similar to adrenaline — which then prompts the fat cells to produce dopamine.
This dopamine travels to the brain, where it helps form a lasting memory that links the smell of the food to illness, causing the fly to avoid it in the future.
Fat tissue acts as a direct messenger between immunity and behavior
The findings challenge the idea that learned food avoidance depends only on the brain or immune system, showing instead that fat tissue actively processes and transmits danger signals.
In experiments, flies initially chose food laced with harmful bacteria because it smelled appealing, but within minutes of eating it, they switched to avoiding it — even when taste played no role.
The shift happened fast, suggesting a rapid communication pathway from gut to brain via head fat cells, which the researchers say mirrors mechanisms likely present in other animals.
This mechanism may explain long-lasting food aversions in humans
Because similar neural-fat-immune pathways exist in mammals, the study offers a plausible biological basis for why humans often develop permanent dislikes to foods that once made them sick — sometimes triggered by smell alone.
It also suggests that metabolic tissues like fat are not just passive storage sites but active participants in learning and behavior, potentially influencing dietary choices long after an illness.
Why did the flies avoid the food even if it tasted the same?
The source states that both food options were initially identical in taste and smell, but after consuming the bacteria-laced food, the flies avoided it based on learned association — not taste — because the immune-fat-brain pathway created a memory linked to the smell.
Could this apply to how humans develop food aversions?
The researchers note that since this type of learned avoidance is found across animal species, and the mechanisms involve conserved systems like immunity, nervous tissue, and fat signaling, it is likely that similar processes operate in humans — though the study was conducted in fruit flies.
