A small study has found that your nose could be telling you to make better food choices.
Researchers found that 30 people were more sensitive to the smells of pizza and cinnamon buns when they ate them while still hungry.
Everybody who has ever tried to taste food with their nose knows that their senses of smell can have an impact on how it tastes. But, new research shows that our senses of smell can be influenced by how foods taste, leading us to choose certain foods over others.
Researchers believe this is the brain's way to ensure we don't overeat, which could be an adaptive strategy to maximize our food search.
Thorsten Kahnt, a neurologist at Northwestern University, says that if you think of our ancestors wandering through the forest looking for food, then they find and eat berries. After that, they are less sensitive to the scent of berries.
"But they might still be sensitive to the scent of mushrooms. It could theoretically help facilitate diversity and nutrient intake."
Previous studies showed that our subjective opinions about whether certain foods are pleasant or not depended on what we ate. However, this study sought out to find out if hunger and satiation affect our sense of smell.
This idea has been explored in only a handful of animal studies and one human study. There are many unanswered questions.
For instance, research on rodents has shown that fasting can affect the activity of the olfactory bulbs, which process smells in the brain.
In 2019, the same researchers discovered that sleep deprivation can cause high-energy foods to smell sharper in the insular cortex. This is a part the olfactory pathway which responds to food-related stimuli.
Although these results are preliminary, they suggest that our appetite may influence our sensitivity to certain smells.
Researchers had 30 participants arrive hungry at the lab after having fasted for at minimum six hours. These volunteers were placed in an MRI scanner and presented with a series 10 smells. One was pizza, the other was cinnamon buns or pine, while the third was cedar or pine.
Participants determined which of the 10 odor mixtures was dominant, and the ratio of food to nonfood was different for each sample.
The volunteers were then served a meal consisting of pizza or cinnamon buns, before returning to the MRI machine.
Laura Shanahan, a Northwestern neurologist and first author of the study, says that she was preparing the meal in another area while the first part of the experiment ran in the MRI scanner.
"We wanted everything to be fresh, ready and warm so that the participants could eat as much as possible until they felt full."
Participants could quickly recognize odors that were more pure (when only one smell was dominant). However, participants were able to identify odors with more purity when there was a mix of smells. Participants also noticed that what they ate at the lab had an effect on their perceptions.
For example, those who were served pizza were less likely than others to smell pine when the pizza was mixed with pine. Those who ate cinnamon buns more often were less likely to notice the baking goods mixed with cedar.
These same participants were still hungry at the beginning of the day but were able to pick out the predominant odor much more easily.
One participant might only have required half the smell of pizza to perceive pine as dominant. Later, however, after the same participant had consumed their pizza, they may have required 80 percent of that odor to make it smell like pizza.
Researchers noticed a similar pattern in the brain when they examined the results of the MRI machines.
These scans showed that different olfactory pathways were activated after meals than they are before. Participants responded less to the sweet scent of cinnamon buns after eating them.
Unfortunately, MRI brain scans cannot measure neural activity directly in a olfactory bulb. This means that we don't really know what causes these changes in our odor perception.
Kahnt says, "We're looking into how that information is altered and how the altered information can be used by the rest the brain to make food intake decisions."
The study was published by PLOS Biology.
