A hormone produced by the stomach makes people want to eat by making food more appealing, which could be a factor in overeating and obesity, a new Canadian study suggests.
The findings from the study, conducted by researchers from Montreal's McGill University, were published in the journal Cell Metabolism.
Researchers gave the hormone, known as ghrelin, through an intravenous drip to a group of study subjects and gave a placebo to others. Both groups viewed pictures of food before and after receiving the hormone or placebo.
By using functional magnetic resonance imaging (fMRI) to measure brain activity, the researchers found that ghrelin increased activity in parts of the brain that process food cues.
"What ghrelin does to the brain is it enhances the response of the brain to food pictures, which we use as a cue to trigger appetite," one of the study's authors, Dr. Alain Dagher of McGill, told CTV's Avis Favaro.
"So when we look at food pictures and you have high ghrelin levels in your body, the greater effect on your brain. And it has a greater effect on the areas of the brain involved in pleasure and motivation -- in other words, it makes food more appealing, more appetitive and more motivating."
Ghrelin is a hormone that the stomach produces to trigger hunger. Researchers had previously thought that it solely kick-started a need to feed. However, this new study found that ghrelin works in parts of the brain that are also triggered in drug addicts, which stimulates an almost addictive reaction to food.
As well, stress encourages the stomach to produce more ghrelin, which could explain the link between stress and obesity, Dagher said.
Judging the value of food by how it looks may have once helped humans adapt during times when food was less abundant, Dagher said.
However, in the age of supermarkets and corner convenience stores, this manner of assessing food may cause us to eat more than we need. This, of course, can lead to obesity and its related health problems.
These findings could have an impact on the current obesity epidemic by leading to treatments that curb the effects of ghrelin. However, the side effects of such treatments could include mood imbalances, because the hormone works in the brain's pleasure centres.
On the other hand, ghrelin injections could help make food more appealing to people who suffer from anorexia. Boosting ghrelin levels could also help cancer patients whose treatments have made them stop eating.
Dr. Mehran Anvari of McMaster University said that the fact that ghrelin levels increase when we are hungry may explain why diets have high failure rates.
"When people diet and lose weight, ghrelin levels go up, and it makes people feel more hungry and every food is more appealing," Anvari said.
Conversely, the stomach produces less ghrelin after surgery has been performed to reduce its size.
The findings also suggest that banning junk-food advertising aimed at children and making unhealthy foods unavailable in cafeterias could help curb obesity in children.
With a report by CTV's medical correspondent Avis Favaro and producer Elizabeth St. Philip.
Summary:
Ghrelin Modulates Brain Activity in Areas that Control Appetitive Behaviour
Saima Malik, Francis McGlone, Diane Bedrossian, and Alain Dagher
Feeding behavior is often separated into homeostatic and hedonic components. Hedonic feeding, which can be triggered by visual or olfactory food cues, involves brain regions that play a role in reward and motivation, while homeostatic feeding is thought to be under the control of circulating hormones acting primarily on the hypothalamus. Ghrelin is a peptide hormone secreted by the gut that causes hunger and food consumption. Here,we show that ghrelin administered intravenously to healthy volunteers during functional magnetic resonance imaging increased the neural response to food pictures in regions of the brain, including the amygdala, orbitofrontal cortex, anterior insula, and striatum, implicated in encoding the incentive value of food cues. The effects of ghrelin on the amygdala and OFC response were correlated with self-rated hunger ratings. This demonstrates that metabolic signals such as ghrelin may favour food consumption by enhancing the hedonic and incentive responses to food-related cues.
