The hormone ghrelin makes us more susceptible to appealing food smells, a phenomenon that encourages overeating and obesity, according to new research.
Earlier work by Alain Dagher’s lab at the Montreal Neurological Institute and Hospital of McGill University and colleagues demonstrated that ghrelin encourages eating and the production of dopamine, a neurotransmitter that is important for reward response.
In the current study, researchers injected 38 subjects with ghrelin, and exposed them to a variety of odors, both food and non-food based, while showing them neutral images of random objects, so that over time subjects associated the images with the odors.
Reward Prediction Activity
Using functional magnetic resonance imaging (fMRI), the researchers recorded activity in brain regions known to be involved in reward response from dopamine.
They found that activity in these regions was higher in subjects injected with ghrelin, but only when responding to the images associated with food smells. This means that ghrelin is controlling the extent to which the brain associates reward with food odors.
[caption id="attachment_98160” align="aligncenter” width="680”] Ghrelin Increases RPE-Associated Activity during Food Odor Conditioning.
Credit: Jung Eun Han, et al. CC-BY[/caption]
Subjects also rated the pleasantness of the images associated with food odor, and the results show that ghrelin both reduced the response time and increased the perceived pleasantness of food-associated images, but had no effect on their reaction to images associated with non-food odors.
People with obesity often have abnormal reactivity to the food-related cues that are abundant in our environment, for example fast food advertising. This study shows that ghrelin may be a major factor in their heightened response to food cues.
The brain regions identified have been linked to a neural endophenotype that confers vulnerability to obesity, suggesting a genetically-based hypersensitivity to food-associated images and smells.
“Obesity is becoming more common around the world and it’s well known to cause health problems such as heart disease and diabetes. This study describes the mechanism through which ghrelin makes people more vulnerable to hunger-causing stimuli, and the more we know about this, the easier it will be to develop therapies that counteract this effect,”
The research was funded by a grant from the Canadian Institutes of Health Research.
Jung Eun Han, Johannes Frasnelli, Yashar Zeighami, Kevin Larcher, Julie Boyle, Ted McConnell, Saima Malik, Marilyn Jones-Gotman, Alain Dagher Ghrelin Enhances Food Odor Conditioning in Healthy Humans: An fMRI Study Cell Reports December 4, 2018 DOI:https://doi.org/10.1016/j.celrep.2018.11.026
Top Image: Ghrelin Strengthens Hippocampus-Ventral Striatum Coupling. Credit: Jung Eun Han, et al. CC-BY