Hunger harmone Responsible for over eating

Hunger hormone ghrelin might drive people to eat even when they are full, says a new study.

"What we show is that there may be situations where we are driven to seek out and eat very rewarding foods, even if we're full, for no other reason than our brain tells us to," said study co-author Jeffrey Zigman.

Scientists previously have linked increased levels of ghrelin to intensifying the rewarding or pleasurable feelings one gets from cocaine or alcohol.

Zigman, assistant professor of psychiatry at University of Texas (UT) Southwestern Medical Centre, said his team speculated that ghrelin might also increase specific rewarding aspects of eating. Rewards, he said, generally can be defined as things that make us feel better.

"They give us sensory pleasure, and they motivate us to work to obtain them," he said. "They also help us reorganise our memory so that we remember how to get them."

Mario Perello, postdoctoral researcher in internal medicine, study co-author, said the idea was to determine "why someone who is stuffed from lunch still eats - and wants to eat - that high-calorie dessert."

For this study, researchers evaluated whether mice that were fully sated preferred a room where they had previously found high-fat food over one that had only offered regular bland chow.

They found that when mice in this situation were administered ghrelin, they strongly preferred the room that had been paired with the high-fat diet. Mice without ghrelin showed no preference.

"We think the ghrelin prompted the mice to pursue the high-fat chow because they remembered how much they enjoyed it," Perello said. "It didn't matter that the room was now empty; they still associated it with something pleasurable."

For the second test, the team observed how long mice would continue to poke their noses into a hole in order to receive a pellet of high-fat food.

"The animals that didn't receive ghrelin gave up much sooner than the ones that did receive ghrelin," Zigman said, according to an UT release.

The next step, Perello said, is to determine which neural circuits in the brain regulate ghrelin's actions.

These findings appeared online in Biological Psychiatry.