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Taste the Difference (video)
December 10, 2002

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Interviewees: Jill Henninger, Patient; Nora Volkow, Brookhaven National Laboratory; Allan Geliebter, St. Luke’s Roosevelt Hospital’s Obesity Research Center.

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Produced by Sanjanthi Velu

Copyright © ScienCentral, Inc., with additional footage from NBC News.

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Is it possible that overweight people get more pleasure from eating?

As this ScienCentral News video reports, studies indicate this may be why some people overeat.

Brain imaging reveals clues on overeating

New brain imaging studies at the U.S. Department of Energy’s Brookhaven National Laboratory have revealed that parts of the brain responsible for sensation in the mouth, lips and tongue are more active in obese people than in the normal-weight control subjects. Could this be the reason why obese people eat more?

In earlier studies the Brookhaven scientists looked at the link between obesity and dopamine receptors in the brain. Gene-Jack Wang, a physician at Brookhaven Labs, Nora Volkow, a senior scientist there, and their co-researchers found that obese people have fewer brain receptors for dopamine, a neurotransmitter that helps produce feelings of satisfaction and pleasure. The study inferred that obese people tend to eat more because it makes them feel happy and this may be satisfying their under-served reward circuits.

In the new study Wang and his team looked at the overall brain metabolism. Wang, lead author in the study that appeared in the journal NeuroReport, recruited 10 severely obese volunteers and 20 normal weight control volunteers, and made them fast for 16 hours. The researchers then used positron emission tomography (PET) to scan the brains of the volunteers, to see if there was any difference in their regional brain metabolism when they were hungry.

But they first injected the volunteers with a radioactively-labeled form of glucose, the brain’s metabolic fuel. Volkow explains, “When your brain is very active it consumes a lot of sugar and when a particular area of the brain is more active than the other, then it consumes more.” So this radioactive tracer acts like glucose in the brain, concentrating in regions where there is high metabolic activity. The PET scan picks up the radioactive signal to reveal where the tracer is located. Then they averaged the PET data of subjects within each group (obese and normal-weight) and compared the results to see if there was a difference between them.

“And to our surprise there were significant differences, but in the area of the brain that is actually responsible for the sensation of food,” says Volkow. They generated 3-dimensional images to look at these areas of higher metabolic activity and superimposed them onto a magnetic resonance image (MRI) of the whole brain, as well as onto a diagram of the brain’s somatosensory cortex, the area of the brain that receives sensory input from various organs.

They found that obese people, in the fasting state, had higher metabolic activity than lean people in areas of the brain where sensory input from the mouth, tongue and lips is received. Wang says this is also an area involved with taste perception.

"One of the reasons that people who are obese are particularly vulnerable to taking food as a re-enforcer, as something pleasurable, is because their brains are particularly sensitive to the sensation, to the pleasurable sensation associated with taking food,” says Volkow.

However, Wang acknowledges that obesity is a complex phenomenon. “Its not one or two mechanisms that will make people eat,” he says, adding that this requires further study. But, “taken together with the earlier results of dopamine deficiency, this increased sensitivity to food palatability is likely to increase the rewarding properties of food, thus making obese people eat even more,” he says.

The study was funded by the U.S. Department of Energy, and the National Institute on Drug Abuse.

by Sanjanthi Velu

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