Research: smell may be the key to our balanced diet

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But according to a new study, the food you eat before passing by the bakery may affect you The possibility of stopping for sweets-not just because you are full.

Scientists at Northwestern University in the United States have discovered that people’s sensitivity to food smells is reduced by the food they have just eaten. So if you eat your colleague’s baked goods before taking a walk, you may be less likely to stop and go to the fragrant bakery.

Smell controls what we eat, and vice versa

Studies have found that participants who have just eaten a meal of cinnamon buns or pizza are less likely to smell “matching food” odor. The results of a brain scan confirmed this finding, which showed that the part of the brain that processes odor has changed in a similar way.

These findings suggest that just as smell regulates what we eat, what we eat in turn regulates our sense of smell.

Thorsten Kahnt, assistant professor of neurology, psychiatry, and behavioral sciences at Northwestern University’s Feinberg School of Medicine, said that feedback between food intake and the olfactory system may be good for evolution.

“Think about our ancestors wandering in the forest looking for food. They found and ate berries, and then they are no longer so sensitive to the smell of berries,” Kahnt said, “but maybe they are still aware of the smell of mushrooms. Sensitive, so theoretically, this may help promote the diversity of food and nutrient intake.”

Kahnt pointed out that although we do not see hunting-gathering adaptation in our daily decision-making, but The connection between our nose, what we are looking for, and what we can detect with our nose may still be very important. For example, if the nose is not working properly, the feedback loop may be interrupted, which can lead to eating disorders and obesity problems. It may even be related to sleep disruption, which is another connection related to the olfactory system that Kahnt’s laboratory is studying.

The Kahnt laboratory uses brain imaging, behavioral testing, and non-invasive brain stimulation to study how the sense of smell can guide learning and appetite behavior, especially when it is associated with mental illnesses such as obesity, addiction, and dementia. In a past study, the research team found that the brains of participants who were sleep deprived changed their response to odors. Next, they wanted to know whether and how food intake changed our ability to perceive food odors.

According to Laura Shanahan, a postdoctoral researcher in the Kahnt laboratory, there are few studies on how odor perception changes due to different factors. “There are some studies on odor pleasure,” Shanahan said, “but our work focuses on people’s sensitivity to these odors in different states.”

Pizza and pine; cinnamon and cedar


To conduct this research, the research team developed a new task that asked participants to smell a mixture of food and non-food odors (“pizza and pine” or “cinnamon bun and cedar”– It matches well and smells different from each other). From pure food to non-pure food, the ratio of food to non-food odor in each mixture is different. After the mixed odors appeared, participants were asked whether food odors or non-food odors were dominant.

Participants completed two tasks in the MRI scanner: the first time when they were hungry, and then after they ate a meal that matched the two odors.

“I was cooking in another room while the MRI scanner was performing the first part of the experiment,” Shanahan said. “We want everything to be fresh, prepared and hot. Because we want participants to eat as much as possible until they are very full.”

Research: smell may be the key to our balanced diet

Then, the research team calculated how much food odors were needed in each phase of the mixture to make participants think that food odors were dominant. The research team found that when participants were hungry, they needed a lower proportion of food odors to be able to see it as the dominant odor–for example, hungry participants might need 50% of the cinnamon bun and cedar mixed odor when they were hungry. If you are full, you need 80%.

Through brain imaging, the research team provided further evidence for this hypothesis. MRI brain scans showed that similar changes occurred in the part of the brain that processes odors after meals. The brain’s response to odors that match the odor of food is more “food-like” than its response to non-food odors.

Applying the research results to future sleep deprivation research

The findings of this research will also allow Kahnt Labs to conduct more complex projects. Kahnt pointed out that with a better understanding of the feedback loop between odor and food intake, he hopes to bring the full cycle of this project back to sleep deprivation, to see if lack of sleep can damage this cycle in some way. He added that with brain imaging technology, there are more questions about how adaptation affects the brain’s sensory and decision-making circuits.

“After a meal, the olfactory cortex no longer represents the food smell that matches the food like food, so adaptation seems to happen relatively early in the processing process,” Kahnt said. “We are tracking how this information changes. And how other parts of the brain use this changed information to make decisions about food intake.”