Small Study Suggests Gut Hormone Heightens Response to Food

The sights and smells of food can be hard to resist. A new, small study posits that one factor in this hunger response is a hormone found in the stomach that makes us more vulnerable to tasty food smells, encouraging overeating and obesity.

New research on the hormone ghrelin, led by Alain Dagher, MD’s lab at the Montreal Neurological Institute and Hospital of McGill University, is published in Cell Reports.

Previous research by Dagher’s group and others demonstrated that ghrelin encourages eating and the production of dopamine, a neurotransmitter that’s 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 nonfood based, while showing them neutral images of random objects, so that over time subjects associated the images with the odors.

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.

Subjects also rated the pleasantness of the images associated with food odor, and the results showed 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 nonfood odors.

People struggling 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.

“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,” Dagher says.

— Source: McGill University