Eating When Already Full? Study Finds That Brain Circuits Involving Sense of Smell, Behavior Motivation Could Explain Why

Researchers have discovered that eating even when full could be linked to behavior motivation and sense of smell.

The researchers reported that food ends up becoming less attractive when a person is already full.

Why Some People Still Eat Even When Full

Scientists may have been able to discover one reason why some people find it easier to stop eating when full compared to others. They think that this is due to the sense of smell and the neural reward systems against negative feelings.

The brain connection of such areas could also control such feelings.

The "Structural connectivity between olfactory tubercle and ventrolateral periaqueductal gray implicated in human feeding behavior" study says that the theory is grounded on a newly found structural link between two areas of the brain that are apparently involved in feeding behavior regulation.

As part of the study, the researchers made use of neural imaging from a project of the National Institutes of Health. The project, known as the Human Connectome Project, was meant for mapping the human brain.

The study authors discovered that weaker links between the two sensory brain regions affected the body mass index of a person (BMI), making it higher.

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Brain Circuits and Eating Habits

The study mainly links the olfactory tubercle, which is an area of the reward system that is linked to smell, and the periaqueductal gray (PAG) midbrain region, which plays a role in behavior motivation responses to negative feelings and possibly eating suppression.

Research has revealed that when a person is hungry, the smell of food is appetizing and appealing. However, this smell becomes less attractive when a person eats until feeling full.

This recent study showed that odors play a crucial role in guiding certain motivated behaviors, like eating. In turn, it appears that hunger may modulate olfactory perception.

Guangyu Zhou, a research assistant neurology professor from the Northwestern University Feinberg School of Medicine and a corresponding author of the study, says that wanting to eat is linked to the appeal of the smell of food. Food may smell better when a person is hungry compared to when a person is full.

However, if there are disruptions in the brain circuits that aid in guiding this behavior, the signals could end up getting confused. This could make food feel rewarding even when a person is already full.

Such a reward sensation linked to food could potentially increase the BMI of a person.

Zhou said that they found that when the two brain regions share a weaker structural connection, the person has a higher BMI.

The study authors think that healthy brain connections that link reward areas with behavioral areas may regulate feeding behavior. It may do so by relaying messages that indicate that eating no longer feels good when a person is full.

The researchers note that individuals who had weak or disrupted connection circuits may end up not receiving the signals to stop, prompting them to eat more even when they are not hungry.

Christina Zelana, an associate neurology professor from Feinberg and a senior study author, says that understanding such basic brain processes is crucial for further work to lead to overeating treatments.

Zhou explained that they were able to find correlations with BMI within the circuit between the PAG and the olfactory tubercle.

Zelano said that further study is necessary to delve into the brain mechanisms that regulate feeding behavior.

Different Reasons For Overeating

Emily Spurlock, a registered dietitian from the Institute of Digestive Wellbeing, who specializes in weight management and gut health, says that the study shows that some people eat for reasons besides hunger.

Spurlock also explains that when a person overeats for the first time to the point of feeling uncomfortable, they may acknowledge. However, if it keeps on happening, they may end up getting desensitized.

Eventually, overeating may no longer feel as uncomfortable as it initially was. Spurlock also explains that the brain connection ends up getting "broken" due to frequent ignoring or overwriting with overeating.

Spurlock, who was not involved in the study, shares questions of whether the connection could be rebuilt or if it could be possible to build a stronger connection.