How Does our Sense of Smell Alter Our Food Intake?

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Researchers have shown how different motivational states (fasted vs sated) can affect a person’s sense of smell and ultimately their food choices.

Humans have long since relied on their sense of smell to look for food. Whether you talk about the early humans hunting for food, or a hungry child looking for hidden cookies, all make use of their noses. However, researchers argue that while our sense of smell can regulate what we eat, what we eat can in turn also regulate our sense of smell.

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. But maybe they’re still sensitive to the smell of mushrooms, so it could theoretically help facilitate diversity in food and nutrient intake.

Professor Thorsten Kahnt, study author

A team of researchers at Northwestern University recruited 30 participants aged 18 to 30 years. They presented the participants with a series of 10 smells containing a mixture of food and non-food odour. For example, cinnamon bun or pizza and cedar or pine. The participants, in their fasting state, then determined which odour was most dominant: pizza or pine, or cinnamon or cedar. Moreover, participants completed the various tasks while inside an MRI scanner. This allowed the researchers to identify neural activity in response to odours.

The participants completed the task twice; first, in a fasted state and then after eating a meal matching one of the two odours. Furthermore, the researchers varied the ratio of food to non-food odours in the 10 samples. This allowed the researchers to determine how much food odour was required for the participant to perceive it as dominant.

Ate Pizza? Less Likely to Smell Pizza

According to the results, the participants more easily perceived the food odour as dominant while hungy. Even when it was present in a lower percentage. Whereas when the same sample was presented to them after they had had their meal, they required a much higher ratio of food odour to perceive it as dominant.

For example, people who had eaten a meal of pizza, had a difficult time identify the pizza scent from the pine. However, in their hungry state, they had no trouble making out the pizza smell as the dominant odour. Moreover, they needed 80% of the sample to smell like pizza for them to perceive it as dominant.

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.

Professor Thorsten Kahnt, study author

The researchers noted a similar pattern when they examined the results from the MRI scans. They observed the activation of different olfactory pathways before and after a meal. Moreover, the brain’s response was less ‘food-like’ after the participant had eaten cinnamon buns or pizza. Thus, further proving the researchers’ hypothesis.

Reference:

Shanahan LK, Bhutani S, Kahnt T (2021) Olfactory perceptual decision-making is biased by motivational state. PLoS Biol 19(8): e3001374. https://doi.org/10.1371/journal.pbio.3001374

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