Researchers
find clues to why some continue to eat when full
Research by (from left)
Drs. Mario Perello, Michael Lutter, Jeffery Zigman and their
colleagues at UT Southwestern Medical Center in Dallas suggests
that there are situations in which our brains drive us to seek out
and eat very rewarding foods, even if we're full. Credit: UT
Southwestern
Monday, December 28, 2009
The premise that hunger makes food look more appealing is a widely
held belief – just ask those who cruise grocery store aisles on an
empty stomach, only to go home with a full basket and an empty
wallet.
Prior research studies have suggested that the so-called hunger
hormone ghrelin, which the body produces when it's hungry, might
act on the brain to trigger this behavior. New research in mice by
UT Southwestern Medical Center scientists suggest that ghrelin
might also work in the brain to make some people keep eating
"pleasurable" foods when they're already full.
"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 Dr. Jeffrey
Zigman, assistant professor of internal medicine and psychiatry at
UT Southwestern and co-senior author of the study appearing online
and in a future edition of Biological
Psychiatry.
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, 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 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."
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."
The researchers also found that blocking the action of ghrelin,
which is normally secreted into the bloodstream upon fasting or
caloric restriction, 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.
###
UT Southwestern Medical Center
Thanks to UT Southwestern Medical Center for this article.
