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Why We Eat Even When We Are Full

Why We Eat Even When We Are Full

When it comes to food why are we greedy? Why do we eat even after we’re full?

When shopping for groceries on an empty stomach, it’s quite common for our eyes to become bigger than our stomachs and our wallets. Previous research suggests that a hunger hormone called ghrelin, produced when the body needs food, may act on the brain to trigger this type of behavior.

Now, new research in mice UT Southwestern Medical Center scientists suggests that ghrelin might also work in the brain to make some people keep eating “pleasurable” foods when they’re already full.

Jeffrey Zigman, assistant professor of internal medicine and psychiatry at UT Southwestern and co-senior author of the study said:

“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,”

Scientists previously have linked increased levels of ghrelin to intensifying the rewarding or pleasurable feelings one gets from cocaine or alcohol. Dr. Zigman said his team speculated that ghrelin might also increase specific rewarding aspects of eating.

Rewards, Dr. Zigman explained, 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. They also help us reorganize our memory so that we remember how to get them.”

Dr. Mario Perello, postdoctoral researcher in internal medicine and lead author of the current study, said:

“The idea was to determine why someone who is stuffed from lunch still eats – and wants to eat – that high-calorie dessert.”

why we eat even when full Why We Eat Even When We Are Full For this study, the researchers conducted two standard behavioral tests. In the first, they 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,” Dr. Perello said. “It didn’t matter that the room was now empty; they still associated it with something pleasurable.”

Further supporting their theory, researchers also found that blocking the action of ghrelin prevented the mice from spending as much time in the room they associated with the high-fat food.

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,” Dr. Zigman said.

Humans and mice share the same type of brain-cell connections and hormones, as well as similar architectures in the so-called “pleasure centers” of the brain. In addition, the behavior of the mice in this study is consistent with pleasure- or reward-seeking behavior seen in other animal studies of addiction, Dr. Zigman said.

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

The study will be published both online and in a future edition of Biological Psychiatry.


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