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Researchers at UT Southwestern Medical Center discovered why some people who are stuffed from lunch still eats and wants to eat.

The study suggest that the so-called appetite stimulator hormone ghrelin might work the brain to make some people keep eating “pleasurable” foods when they are already full.

Ghrelin boost the visual cues through action on the brain reward centers including: Amygdala, Insula, and Orbitofrontal Cortex. These areas are responsible for pleasure sensation. Affecting these areas causes foods to be more appealing to a person.

Dr. Jeffrey Zigman, assistant professor of internal medicine and psychiatry at UT Southwestern speculated that ghrelin might also increase specific rewarding aspects of eating.

The study was conducted by doing two standard behavioral tests on mice. They evaluated in the first test whether completely satisfied mice preferred a room where they had previously found high-fat food over one that had only regular bland food. They discovered that mice administered by ghrelin preferred the room with high-fat diet while mice without ghrelin showed no preference.

In the second test, they observed how long mice would continue to poke their noses into a hole in order to receive a shot of high-fat food. The animals that did not receive ghrelin gave up sooner than the ones that receive ghrelin.

Prior research suggested that caloric restriction or fasting, secretes ghrelin into the bloodstream suppressing its action.