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Research - journal of The
North American Association for the Study of Obesity
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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
Brain imaging reveals clues on overeating
New brain imaging studies at the U.S. Department of Energyâ€™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?
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
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
But they first injected the volunteers with a radioactively-labeled form of
glucose, the brainâ€™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 brainâ€™s
somatosensory cortex, the area of the brain that receives sensory input from
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
"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.