Hormone in Gut Increases Response to Food, Researchers Find

The holiday season is a hard one for anyone watching their weight. The sights and smells of food are hard to resist.

One factor in this hunger response is a hormone called ghrelin, which is found in the stomach that makes us more vulnerable to tasty food smells, encouraging overeating and obesity.

Now, researchers in Canada are doing studies to better understand the response of the hormone to food.

Previous research has shown that ghrelin encourages eating and the production of dopamine, a neurotransmitter that is important for reward response in the brain.

“Obesity is becoming more common around the world and it’s well known to cause health problems such as heart disease and diabetes,” says Dr. Alain Dagher of the Montreal Neurological Institute and Hospital of McGill University.

“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, he explains.”

What did they Study?

In the McGill University study, researchers injected 38 subjects with ghrelin, and exposed them to a variety of smells, both food and non-food based, while showing them neutral images of random objects, so that over time, the subjects associated the images with the smells.

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.

According to researchers, this means that ghrelin is controlling the extent to which the brain associates reward with food smells.

Subjects also rated the “pleasantness” of the images associated with food smell, 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 non-food odors.

What do the Findings Mean?

The research shows 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 suggests 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,” the researchers state.

Scientists hope that better understanding the hormone responsible for hunger cues will one day help them develop therapies to counteract this effect, which will have a large impact on the obesity epidemic.

This study was published open access in Cell Reports.