The team used a scale to determine the amount of icing needed to cover each cinnamon roll. Credit: Beth MacDonald/Unsplash
You might be tempted to walk past a bakery as the sweet smell wafting out of the front door may draw you in. This is not a common occurrence: Major brands such as Panera Bread and Cinnabon have made huge sales by introducing baked goods to their restaurants.
A new study has shown that the food you eat just before you walk by the bakery can impact your chances of stopping by for a sweet treat.
Northwestern University scientists discovered that people are more sensitive to food odors depending on what they ate just before. For example, if you had a snack of baked goods from a colleague before you started walking, it may make you less likely to go into that sweet-smelling bakery.
The study "Olfactory perceptual decisions-making is biased due to motivational state" will be published in PLOS Biology on August 26th.
What we eat is regulated by our sense of smell, and vice versa
Participants who had just eaten pizza or cinnamon buns were less likely than those who had not. Brain scans showed that brain activity in the brains of those who process odors was also altered, corroboring these findings.
These results show that our sense of smell is just as important in regulating what we eat.
Thorsten Kahnt (senior and corresponding study author), an assistant professor of neurology, psychiatry, and behavioral sciences at Northwestern University Feinberg Schools of Medicine, suggested that feedback between food intake and the sense of smell may be evolutionary beneficial.
Kahnt stated that if you think of our ancestors wandering through the forest looking for food, then they are less sensitive to the scent of berries. But they might still be sensitive to the scent of mushrooms so it could theoretically facilitate diversity in food intake and nutrient intake.
Kahnt stated that while we may not see hunter-gatherer adaptation in our day-to-day decisions-making, the link between our nose and what we seek to find, as well as what we can sense with our nose, could still be vital. The feedback loop can be disrupted if the nose doesn't work properly, which could lead to disordered eating or obesity. The Kahnt lab is also looking into disrupted sleep.
The Kahnt Lab studies the effects of the senses of smell on learning and appetite, especially in relation to mental conditions such as obesity, addiction, and dementia. They use brain imaging, behavioral testing, and non-invasive brain stimulation. The team discovered that the brain's response is affected in sleep-deprived subjects. Next, they wanted to determine if and how food intake affects our ability to detect food smells.
Laura Shanahan is a postdoctoral fellow at the Kahnt laboratory and the co-corresponding author. She says that there is very little research on how perceptions of odor change due to various factors. Shanahan stated that there is some research into odor pleasantness, but our focus is on how sensitive you can be to these odors in different state.
Pizza and pine; cinnamon, and cedar
The team devised a new task to conduct the study. Participants were given a mixture of a food and non-food smell. This included "pizza and pine", "cinnamon bun, cedar" odors that "pair well" but are different from one another. Each mixture had a different ratio of food and nonfood odors, ranging from pure food to pure food. Participants were asked to choose which non-food or food odor they preferred after a mixture was shown.
Participants performed the task twice in an MRI scanner. First, they had to be hungry. Then, they had to eat a meal that matched either of the two odors.
Shanahan stated, "In parallel to the first part of experiment running in MRI scanner. I was preparing meal in another area." "We wanted everything to be fresh and warm so that the participant could eat as much as possible until they felt full.
The team calculated how much food smell was needed in each session to make the participant perceive it as dominant. Participants who were hungry needed less food odor to perceive the mixture as dominant. For example, a participant might need a cinnamon bun-to-cedar mix that contains 50 percent when they are hungry and 80 percent when they are full of cinnamon buns.
The team also provided brain imaging evidence to support their hypothesis. Brain scans using MRI showed a parallel change in the brain's ability to process odors after meals. The brain responded less to an odor that was matched to a meal than it did to an odor not matched to a meal.
Future sleep deprivation research will be informed by these findings.
The Kahnt laboratory will be able to tackle more complicated projects thanks to the findings of this study. Kahnt stated that he now has a better understanding about the feedback loop between food intake and smell. He hopes to bring the project back to sleep deprivation to determine if it may affect the loop. Kahnt said that brain imaging raises more questions about the impact of adaptation on sensory and decision-making circuits within the brain.
Kahnt stated that "after the meal, the food-matched odors were not represented by the olfactory cortex anymore. So the adaptation seems to be occurring relatively early in processing." We are examining how this information is altered and how it is used by other parts of the brain to decide about food intake.
Additional information: Laura K. Shanahan and colleagues, Olfactory perceptual decisions-making are biased by motivational states, PLOS Biology (2021). Information from PLoS Biology Laura K. Shanahan et. al., Olfactory perceptual decisions-making are biased by motivational states, (2021). DOI: 10.1371/journal.pbio.3001374
