HEALTH: Link found between obesity and brain receptors

February 1, 2001
Web posted at: 6:30 p.m. EST (2330 GMT)

Elizabeth Cohen
CNN Medical Correspondent

UPTON, New York (CNN) -- Brain scans show that obese people, just like drug addicts, have fewer receptors for dopamine, a neurotransmitter that helps produce feelings of satisfaction and pleasure.

The finding at the Brookhaven National Laboratory has prompted scientists to theorize that one reason people overeat is to stimulate the dopamine "pleasure" circuits in the brain, just as addicts do by taking drugs.

"This is the first scientific contribution that the addictive pathways are deficient in the obese and it may explain their cravings," said Dr. George Blackburn, an associate professor of nutrition at Harvard Medical School.

In the study, scientists measured the number of dopamine receptors in the brains of 10 severely obese individuals and in 10 people with normal weight, by giving each subject an injection containing a radiotracer -- a radioactive chemical "tag" designed to bind to dopamine receptors in the brain. Researchers then scanned the subjects' brains using a positron emission tomography (PET) camera, which picks up radioactive signals. The strength of the signal indicated the number of receptors.

The researchers found that study subjects with the highest Body Mass Index had the fewest number of dopamine receptors. Body Mass Index, or BMI, is a ratio of weight to height.

The study is being published in the journal The Lancet.

Doctors who treat overweight patients welcomed the study as yet more evidence that obesity has physiological causes. Other studies have shown that insulin levels, and levels of a hormone called leptin, also play a role in obesity.

"Obesity is not gluttony," Blackburn explained.

Dr. Richard Atkinson, professor of medicine and nutritional sciences at the University of Wisconsin, agreed.

"This study is important because it tells us more about obesity, gives more evidence that it's not just a failure of willpower. Obesity should be treated like a disease just, like any other disease," he said.

But the doctors were not completely convinced that a lack of dopamine receptors causes obesity -- it could, they said, be the other way around. "It's a little hard to know which is which -- it's like the chicken and the egg," added Atkinson.

They said if future studies show the lack of receptors causes obesity -- and not the other way around -- then scientists could try to develop new drugs that target the receptors.

Those drugs already exist, but doctors often avoid prescribing the compounds, called amphetamines, because they're highly addictive.

The study authors suggest that instead of taking dexamphetamines, obese people could exercise to increase their dopamine levels.

"In animal studies ... exercise has been found to increase dopamine levels and to raise the number of dopamine receptors," said study co-author Dr. Nora Volkow, a psychiatrist at Brookhaven.

Tuesday, August 25, 2009

Study: Obesity Damages Your Brain

A new study finds obese people have 8 percent less brain tissue than normal-weight individuals and their brains look 16 years older. "That's a big loss of tissue and it depletes your cognitive reserves, putting you at much greater risk of Alzheimer's and other diseases that attack the brain," said researcher Paul Thompson of UCLA. "But you can greatly reduce your risk for Alzheimer's, if you can eat healthily and keep your weight under control."

 

A new study finds obese people have 8 percent less brain tissue than normal-weight individuals. Their brains look 16 years older than the brains of lean individuals, researchers said today.

Those classified as overweight have 4 percent less brain tissue and their brains appear to have aged prematurely by 8 years.

The results, based on brain scans of 94 people in their 70s, represent "severe brain degeneration ," said Paul Thompson, senior author of the study and a UCLA professor of neurology .

"That's a big loss of tissue and it depletes your cognitive reserves, putting you at much greater risk of Alzheimer's and other diseases that attack the brain," said Thompson. "But you can greatly reduce your risk for Alzheimer's, if you can eat healthily and keep your weight under control."

The findings are detailed in the online edition of the journal Human Brain Mapping .

Obesity packs many negative health effects , including increased risk of heart disease, Type 2 diabetes, hypertension and some cancers. It's also been shown to reduce sexual activity .

More than 300 million worldwide are now classified as obese, according to the World Health Organization . Another billion are overweight. The main cause, experts say: bad diet , including an increased reliance on highly processed foods .

Obese people had lost brain tissue in the frontal and temporal lobes , areas of the brain critical for planning and memory, and in the anterior cingulate gyrus (attention and executive functions ), hippocampus ( long-term memory ) and basal ganglia (movement), the researchers said in a statement today. Overweight people showed brain loss in the basal ganglia, the corona radiata , white matter comprised of axons, and the parietal lobe (sensory lobe).

"The brains of obese people looked 16 years older than the brains of those who were lean, and in overweight people looked 8 years older," Thompson said.

Obesity is measured by body mass index (BMI), defined as the weight in kilograms divided by the square of the height in meters. A BMI over 25 is defined as overweight, and a BMI of over 30 as obese.

The research was funded by the National Institute on Aging , National Institute of Biomedical Imaging and Bioengineering , National Center for Research Resources , and the American Heart Association .