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• Posted May 17, 2024

Brain's 'Food Smell' Circuitry Might Drive Overeating

The smell of food is appetizing when you're hungry. At the same time, it can be a turnoff if you're full.

That's due to the interaction between two different parts of the brain involving sense of smell and behavior motivation, a new study finds.

And it could be why some people can't easily stop eating when they're full, which contributes to obesity, researchers say.

The weaker the connection between those two brain regions, the heavier people tend to become, results show.

"The desire to eat is related to how appealing the smell of food is -- food smells better when you are hungry than when you are full,"said study co-author Guangyu Zhou, a research assistant professor of neurology at Northwestern University Feinberg School of Medicine in Chicago. "But if the brain circuits that help guide this behavior are disrupted, these signals may get confused, leading to food being rewarding even when you are full."

"If this happens, a person's BMI could increase. And that is what we found,"Zhou added in a Northwestern news release. "When the structural connection between these two brain regions is weaker, a person's BMI is higher, on average."

Odors play an important role in guiding motivation for behaviors like eating, researchers said. At the same time, how you perceive smells can be influenced by how hungry you are.

But until now researchers haven't fully understood the interplay within the brain that causes the sense of smell to contribute to how much you eat.

For the study, published May 16 in the Journal of Neuroscience, researchers analyzed MRI brain data gathered by a larger effort to create a map of the human brain.

Researchers found correlations to BMI in the circuit between two brain regions called the olfactory tubercule and the periaqueductal gray.

The olfactory tubercule is tied to the sense of smell and the brain's reward system, researchers said.

And the periaqueductal gray contributes to motivating behavior in response to negative feelings like pain and threat. This region also is potentially involved in the suppression of eating.

For the first time in humans, the research team mapped the strength of the circuit between these two regions.

Healthy brain connections like this could regulate eating behavior by sending messages telling the person that eating doesn't feel good when they're full. 

However, people with weak or disrupted circuits connecting these areas may not get these signals, and could keep eating even when they aren't hungry, researchers said. 

"Understanding how these basic processes work in the brain is an important prerequisite to future work that can lead to treatments for overeating,"said senior study author Christina Zelano, an associate professor of neurology at Northwestern.

More information

The Cleveland Clinic has more on hunger.

SOURCE: Northwestern University, news release, May 16, 2024