Your sense of smell is stronger when you’re hungry

EVANSTON, Ill. — Does the glorious smell of fresh cinnamon buns or sizzling bacon draw you into your local café for a treat? It turns out that what your nose sniffs out has a lot to do with what your stomach is telling it. Researchers from Northwestern University say your sense of smell is actually stronger when you’re hungry than right after eating a meal.

More specifically, study authors find that a person’s nose becomes less sensitive to the odor of similar foods if they just ate that particular item. For example, people are less likely to crave a cinnamon bun after smelling one if they just ate a sweet treat. Conversely, even a slight hint of cinnamon bun smell will drive someone to go buy one if they haven’t eaten yet.

Brain scans on a group of participants smelling either cinnamon buns or pizza discovered that people are less likely to perceive “meal-matched” odors after eating. The findings reveal that smell not only plays a role in what we eat — what we eat also plays a role in what we smell.

Study authors add that this ability may even help people eat a more balanced diet because their nose will seek out a more diverse menu.

“If you think about our ancestors roaming the forest trying to find food, they find and eat berries and then aren’t as sensitive to the smell of berries anymore,” says senior study author Thorsten Kahnt in a university release. “But maybe they’re still sensitive to the smell of mushrooms, so it could theoretically help facilitate diversity in food and nutrient intake.”

Can smelling problems lead to obesity?

Kahnt adds that the human sense of smell still plays a major role today, just like it did for hunter-gatherers in the past. In fact, when this sense is not working right, the team suggests a lack of smell can even lead to eating disorders or weight issues. In their previous studies, the Northwestern researchers examined how sleep disorders and sleep deprivation affects a person’s ability to smell certain foods.

For the new study, the Kahnt lab team used brain imaging and behavioral testing to see how the brain reacts to food and non-food odors depending on how hungry a person is. Researchers paired “pizza and pine” or “cinnamon bun and cedar,” since the two scents reportedly “pair well” together and are very distinct from one another.

While inside an MRI scanner, participants smelled the pairings in two different instances; the first time when they were hungry and the second after eating that same food. Researchers also changed the amount of food odor each participant was smelling during these scans.

Results show that a hungry participant only needs 50 percent cinnamon bun smell to consider it the dominant smell over cedar. However, it takes 80 percent cinnamon bun smell for the brain to perceive it more than cedar after eating cinnamon buns.

“After the meal, the olfactory cortex didn’t represent meal-matched food odors as much as food anymore, so the adaptation seems to be happening relatively early on in processing,” Kahnt adds. “We’re following up on how that information is changed and how the altered information is used by the rest of the brain to make decisions about food intake.”

The study appears in the journal PLOS Biology.

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