It may guide you to pick something different than what you ate the last time
Northwestern University
You're not alone: The knowledge that humans make decisions based on their nose has led major brands like Cinnabon and Panera Bread to pump the scents of baked goods into their restaurants, leading to big spikes in sales.
But
according to a new study, the food you ate just before your walk past the
bakery may impact your likelihood of stopping in for a sweet treat -- and not
just because you're full.
Scientists
at Northwestern University found that people became less sensitive to food
odors based on the meal they had eaten just before. So, if you were snacking on
baked goods from a coworker before your walk, for example, you may be less
likely to stop into that sweet-smelling bakery.
The
study, "Olfactory perceptual decision-making is biased by motivational
state," will be published August 26 in the journal PLOS Biology.
Smell regulates what we eat, and vice versa
The
study found that participants who had just eaten a meal of either cinnamon buns
or pizza were less likely to perceive "meal-matched" odors, but not
non-matched odors. The findings were then corroborated with brain scans that
showed brain activity in parts of the brain that process odors was altered in a
similar way.
These
findings show that just as smell regulates what we eat, what we eat, in turn,
regulates our sense of smell.
Feedback
between food intake and the olfactory system may have an evolutionary benefit,
said senior and corresponding study author Thorsten Kahnt, an assistant
professor of neurology and psychiatry and behavioral sciences at Northwestern
University Feinberg School of Medicine.
"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," Kahnt said. "But maybe they're still sensitive to the smell
of mushrooms, so it could theoretically help facilitate diversity in food and
nutrient intake."
Kahnt
said while we don't see the hunter-gatherer adaptation come out in day-to-day
decision-making, the connection between our nose, what we seek out and what we
can detect with our nose may still be very important. If the nose isn't working
right, for example, the feedback loop may be disrupted, leading to problems
with disordered eating and obesity. There may even be links to disrupted sleep,
another tie to the olfactory system the Kahnt lab is researching.
Using
brain imaging, behavioral testing and non-invasive brain stimulation, the Kahnt
lab studies how the sense of smell guides learning and appetite behavior,
particularly as it pertains to psychiatric conditions like obesity, addiction
and dementia. In a past study, the team found the brain's response to smell is
altered in sleep-deprived participants, and next wanted to know whether and how
food intake changes our ability to perceive food smells.
According
to Laura Shanahan, a postdoctoral fellow in the Kahnt lab and the first and
co-corresponding author of the study, there's very little work on how odor
perception changes due to different factors. "There's some research on
odor pleasantness," Shanahan said, "but our work focuses in on how
sensitive you are to these odors in different states."
Pizza
and pine; cinnamon and cedar
To
conduct the study, the team developed a novel task in which participants were
presented with a smell that was a mixture between a food and a non-food odor
(either "pizza and pine" or "cinnamon bun and cedar" --
odors that "pair well" and are distinct from each other). The ratio
of food and non-food odor varied in each mixture, from pure food to pure
non-food. After a mixture was presented, participants were asked whether the
food or the non-food odor was dominant.
Participants
completed the task twice inside an MRI scanner: First, when they were hungry,
then, after they'd eaten a meal that matched one of the two odors.
"In
parallel with the first part of the experiment running in the MRI scanner, I
was preparing the meal in another room," Shanahan said. "We wanted
everything fresh and ready and warm because we wanted the participant to eat as
much as they could until they were very full."
The
team then computed how much food odor was required in the mixture in each
session for the participant to perceive the food odor as dominant. The team
found when participants were hungry, they needed a lower percentage of food
odor in a mixture to perceive it as dominant -- for example, a hungry participant
may require a 50% cinnamon bun to cedar mixture when hungry, but 80% when full
of cinnamon buns.
Through
brain imaging, the team provided further evidence for the hypothesis. Brain
scans from the MRI demonstrated a parallel change occurring in the part of the
brain that processes odors after a meal. The brain's response to a meal-matched
odor was less "food-like" than responses to a non-matched meal odor.
Applying
findings to future sleep deprivation research
Findings
from this study will allow the Kahnt lab to take on more complex projects.
Kahnt said with a better understanding of the feedback loop between smell and
food intake, he's hoping to take the project full circle back to sleep
deprivation to see if lack of sleep may impair the loop in some way. He added
that with brain imaging, there are more questions about how the adaptation may
impact sensory and decision-making circuits in the brain.
"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 said. "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."
Funding
for this research was provided by the National Heart, Lung, and Blood Institute
(grant T32HL007909), the National Institute of Diabetes and Digestive and
Kidney Diseases (grant R21DK118503) and the National Institute of Deafness and
other Communication Disorders (grant R01DC015426)