Sugar can be addictive, Princeton scientist says - Animal studies show sugar dependence

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Public release date: 10-Dec-2008

http://www.eurekalert.org/pub_releases/2008-12/pu-scb120908.php

Contact: Kitta MacPherson

kittamac@...

Princeton University

Sugar can be addictive, Princeton scientist says

Animal studies show sugar dependence

A 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

of abuse.

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. "

At the annual meeting of the American College of Neuropsychopharmacology

in sdale, 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

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 sugar addiction.

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. "

Hungry 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.

In 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 disorders.

" 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. "

--

ne Holden, MS, RD

" Ask the Parkinson Dietitian " http://www.parkinson.org/

" Eat well, stay well with Parkinson's disease "

" Parkinson's disease: Guidelines for Medical Nutrition Therapy "

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