By Stacey Young
A hormone that stops us from eating too much could affect
other addictions as well. As this ScienCentral News video
explains, that's the conclusion of researchers studying
people born without the hormone who got replacement therapy.
Overeating in the Brain
researchers looked at brain scans to see leptin activity
in the brain before and after treatment.
If you've ever uttered the words, "I'm
so hungry I could eat a horse," you know it's not
literally possible to chow down on such a huge animal
in one sitting. But have you ever considered what stops
us from being able to do so (besides the scarcity of horsemeat
on most menus)? Scientists say a number of hormones are
at work in alerting us that we've had enough to eat.
Now there's fresh evidence that one of those
alter brain structure in areas associatedwith craving
and addiction in obese individuals born without a gene
that produces leptin.
The researchers looked at brain scans to
see leptin activity in the brain before and after treatment.
"There are very few people who have a genetic mutation,
that they are just born without it…they tend to
eat too much," explains Julio
Licinio, a biobehavioral researcher at UCLA
who, along with a team of UCLA scientists, studied the
only three such people scientists have identified as lacking
the leptin gene. Licinio gave them daily leptin replacement
while his colleague, brain researcher Edythe
London, used MRI brain scans to look at the volunteers'
brain structure before they took leptin, and then at three
and 18 months into the study.
"We found dramatic results in brain
structure," says London. "The actual composition
of the brain changed, but it wasn't all over the brain.
The composition of the brain changed only in regions known
to be related to self control behaviors."
The team reported in the Journal
of Clinical Endocrinology and Metabolism that
the volunteers not only lost 50 percent of their body
weight without the aid of dieting, but also had significant
changes in gray brain matter—the wiring that allows
brain cells to signal the body and each other—in
the inferior parietal lobule, the cerebellum on the left
side of the brain and in the anterior cingulate gyrus.
"The anterior cingulate gyrus is particularly
interesting," says London, who has published a number
of studies on addiction and the brain. "That's because
the anterior cingulate gyrus repeatedly is turned on in
brain imaging studies for craving of other substances:
drugs of abuse, cocaine, tobacco. So we believe that there's
a commonality, between craving food, hunger, craving for
drug—and that leptin may have a fundamental role
in all these types of behaviors."
For now, London admits to being stumped as to how the
brain changes she saw might be linked with cravings: "It's
very hard to know what a structural change like increase
in gray matter could mean. It could mean that the nerve
cells in that part of the brain are larger. It could mean
that the connections have changed in that area of the
And she says she's not even sure leptin
was acting in the brain to cause the changes: "Leptin
may have had an effect somewhere else in the body and
some other factor may have come into the brain to produce
Further study will most likely uncover more;
something London says is key to helping people with food
addictions. "If we understand the biology of addictive
disorders, it goes beyond dealing with anybody that has
a very unique problem with cocaine, methamphetamine or
heroin. It begins to extend to a family of disorders that
include control of food."
But before looking to leptin to help you
loosen your belt, London says to keep in mind the unique
nature of this study group: "We know that leptin
has dramatic affects to reduce weight loss in a genetically
deficient population who don't make leptin on their own,
but there is a lot of variability in the general population.
Prior studies where leptin was used by itself to treat
obesity were not very successful."
Still, she says the findings "give
us some clues, and we have to explore the interaction
between genetics and environment in modulating body weight."
So for now, if you're looking to fit into
that fabulous new wardrobe you'll have to do it the old-fashioned
way…with a good diet and a lot of self-control.
This research was published in February
15, 2005 issue of the Journal
of Clinical Endocrinology and Metabolism and
was funded by the National
Institutes of Health.
Original source: http://www.sciencentral.com