If you’ve ever craved a particular food out of nowhere, you might have your brain to thank. Hunger doesn’t just make us want to eat; it can actually change how we experience flavor and scent. A new study suggests that when the body is missing certain nutrients, the brain tunes its senses to help find what it needs.
Researchers at the Champalimaud Foundation in Portugal discovered this surprising link while studying fruit flies, whose brains are often used to model fundamental biological processes. When the flies were deprived of even one essential amino acid, one of the building blocks of protein, their brains rewired how they processed smells. That shift helped them zero in on food sources rich in the missing nutrients.
The findings, published in Current Biology, reveal just how adaptable the brain can be in maintaining nutritional balance.
“While the flies’ behavior was similar across all amino acid deprivations, showing an increased drive to feed, each deprivation had its own unique ‘fingerprint’ in terms of gene expression,” said Gili Ezra-Nevo, the study’s first author. “But despite those differences, some genes changed in the same way no matter which amino acid was missing.”
In practical terms, the flies’ sense of smell became sharper for certain aromas. When one of the smell receptors was turned off, the insects could still find yeast, their main source of protein, but didn’t eat as much.
“They could smell where it was, but it didn’t taste as good to them,” Ezra-Nevo explained.
The result suggests that smell not only helps locate food but also shapes how appealing that food seems once it’s found.
The researchers also noticed that the smell of fermented foods, like chocolate or cheese, became especially enticing.
“The flies weren’t being attracted to the chocolate itself — they were responding to the bacteria growing in those foods,” said co-first author Sílvia Henriques. “And those bacteria are also natural residents of the fly microbiome.”
By following those scents, the flies were essentially seeking out living microbes that could help them absorb nutrients and survive times of scarcity. The study builds on earlier research showing that beneficial bacteria in the gut can enhance amino acid uptake when diets fall short.
The parallels to people are intriguing. Many of the foods humans crave when hungry, from bread and cheese to yogurt and kimchi, are fermented or rich in amino acids. Scientists have long suspected that such cravings reflect more than habit or comfort. This study hints that our sensory systems, too, may shift in subtle ways when our diets lack key nutrients, nudging us toward what restores balance.
The research was funded by the Champalimaud Foundation.