Contact: Kitta MacPherson
Sugar can be addictive, Princeton scientist says
Animal studies show sugar dependence
Princeton University scientist will present new evidence today
demonstrating that sugar can be an addictive substance, wielding its
power over the brains of lab animals in a manner similar to many drugs
Professor Bart Hoebel and his team in the Department
of Psychology and the Princeton Neuroscience Institute have been
studying signs of sugar addiction in rats for years. Until now, the
rats under study have met two of the three elements of addiction. They
have demonstrated a behavioral pattern of increased intake and then
showed signs of withdrawal. His current experiments captured craving
and relapse to complete the picture.
"If bingeing on sugar is
really a form of addiction, there should be long-lasting effects in the
brains of sugar addicts," Hoebel said. "Craving and relapse are
critical components of addiction, and we have been able to demonstrate
these behaviors in sugar-bingeing rats in a number of ways."
the annual meeting of the American College of Neuropsychopharmacology
in Scottsdale, Ariz., Hoebel will report on profound behavioral changes
in rats that, through experimental conditions, have been trained to
become dependent on high doses of sugar.
"We have the first
set of comprehensive studies showing the strong suggestion of sugar
addiction in rats and a mechanism that might underlie it," Hoebel said.
The findings eventually could have implications for the treatment of
humans with eating disorders, he said.
Lab animals, in
Hoebel's experiments, that were denied sugar for a prolonged period
after learning to binge worked harder to get it when it was
reintroduced to them. They consumed more sugar than they ever had
before, suggesting craving and relapse behavior. Their motivation for
sugar had grown. "In this case, abstinence makes the heart grow
fonder," Hoebel said.
The rats drank more alcohol than normal
after their sugar supply was cut off, showing that the bingeing
behavior had forged changes in brain function. These functions served
as "gateways" to other paths of destructive behavior, such as increased
alcohol intake. And, after receiving a dose of amphetamine normally so
minimal it has no effect, they became significantly hyperactive. The
increased sensitivity to the psychostimulant is a long-lasting brain
effect that can be a component of addiction, Hoebel said.
The data to be presented by Hoebel is contained in a research paper that has been submitted to
The Journal of Nutrition.
Visiting researchers Nicole Avena, who earned her Ph.D. from Princeton
in 2006, and Pedro Rada from the University of Los Andes in Venezuela
wrote the paper with Hoebel.
Hoebel has been interested in the
brain mechanisms that control appetite and body weight since he was an
undergraduate at Harvard University studying with the renowned
behaviorist B.F. Skinner. On the Princeton faculty since 1963, he has
pioneered studies into the mental rewards of eating. Over the past
decade, Hoebel has led work that has now completed an animal model of
Hoebel has shown that rats eating large
amounts of sugar when hungry, a phenomenon he describes as
sugar-bingeing, undergo neurochemical changes in the brain that appear
to mimic those produced by substances of abuse, including cocaine,
morphine and nicotine. Sugar induces behavioral changes, too. "In
certain models, sugar-bingeing causes long-lasting effects in the brain
and increases the inclination to take other drugs of abuse, such as
alcohol," Hoebel said.
Hoebel and his team also have found
that a chemical known as dopamine is released in a region of the brain
known as the nucleus accumbens when hungry rats drink a sugar solution.
This chemical signal is thought to trigger motivation and, eventually
with repetition, addiction.
The researchers conducted the
studies by restricting rats of their food while the rats slept and for
four hours after waking. "It's a little bit like missing breakfast,"
Hoebel said. "As a result, they quickly eat some chow and drink a lot
of sugar water." And, he added, "That's what is called binge eating --
when you eat a lot all at once -- in this case they are bingeing on a
10 percent sucrose solution, which is like a soft drink."
rats that binge on sugar provoke a surge of dopamine in their brains.
After a month, the structure of the brains of these rats adapts to
increased dopamine levels, showing fewer of a certain type of dopamine
receptor than they used to have and more opioid receptors. These
dopamine and opioid systems are involved in motivation and reward,
systems that control wanting and liking something. Similar changes also
are seen in the brains of rats on cocaine and heroin.
experiments, the researchers have been able to induce signs of
withdrawal in the lab animals by taking away their sugar supply. The
rats' brain levels of dopamine dropped and, as a result, they exhibited
anxiety as a sign of withdrawal. The rats' teeth chattered, and the
creatures were unwilling to venture forth into the open arm of their
maze, preferring to stay in a tunnel area. Normally rats like to
explore their environment, but the rats in sugar withdrawal were too
anxious to explore.
The findings are exciting, Hoebel said,
but more research is needed to understand the implications for people.
The most obvious application for humans would be in the field of eating
"It seems possible that the brain adaptations and
behavioral signs seen in rats may occur in some individuals with
binge-eating disorder or bulimia," Hoebel said. "Our work provides
links between the traditionally defined substance-use disorders, such
as drug addiction, and the development of abnormal desires for natural
substances. This knowledge might help us to devise new ways of
diagnosing and treating addictions in people."