A hormone produced in the gut spurs people to eat more by making food seem more appealing, new research reveals, proving the wisdom behind the oft-repeated advice that people should never go food shopping when they are hungry.

"It's something that people knew but this explains it," said senior author Dr. Alain Dagher from Montreal, where he is a neurologist with McGill University's Montreal Neurological Institute.

Dagher and his co-authors showed that the hormone, ghrelin, activates parts of the brain involved in sensations of pleasure or reward -- the same parts of the brain affected when addicts indulge in their drug of choice.

Ghrelin, which the gut generates to tell us we are hungry is also produced when we are under stress, Dagher said, underscoring the aptness of the phrase "comfort food." Eating drives down levels of ghrelin.

"Ghrelin is a gut signal -- it's the way the gut communicates with the brain to make you hungry," explained Dagher, who specializes in the workings of the brain in drug addiction.

"And how it does that is by increasing the rewarding nature of food cues, by making food pictures or food thoughts or food objects more attractive to you. Therefore increasing the probability you will eat."

The work, which was funded by a grant from food and household cleaning products giant Unilever PLC, was published yesterday in the journal Cell Metabolism.

The study was hailed as important by experts who had no involvement in the work, including a University of Miami researcher who has done a similar study looking at the activity stimulated in the brain by the hormone leptin, which tells our brains when we've had enough to eat.

"I think that's where research in this field needs to go, to show how these signals are impacting on brain function," said Dr. Julio Licinio.