A new study suggests that people become obese because
they eat too much and they eat too much because they have weakened reward
circuitry in their brains, which forces them to eat more to get satisfied with
the foods they eat. The theory is plain and simple, but more work is needed.
The study led by Eric Stice and colleagues at the
University of Texas and the University of Oregon and Yale University found that
young females who were positive for a genetic variant and had less activation
in the dorsal striatum part of the brain were more likely to gain weight within
one year of the study.
The study involved 43 female college students ages 18 to
22 with a mean body mass index of 28.6 and adolescents ages 14 to 18 with a
mean BMI of 24.3.
Stice and colleagues
measured how the subjects' brains responded when they were ingesting a
milkshake and tested them for the presence of Taq1A A1 allele.
And then they waited for a year to see how much
weight the subjects gain.
They found subjects who were less excited for the food
they were eating gained more weight after one year. The weight gain was even
more significant in those who were less sensitive to the pleasure from eating
the food and also had the genetic variant.
The results of the study seem to suggest that those who
gained more weight ATE more foods than others because they were less sensitive
to the pleasure from eating food and they would have to eat more to compensate
A health observer suggested that those who gained more
weight did not have to eat more to gain weight.
They could be less physically active than those who gained less weight.
Additionally, the milkshake test is also very limited and
it may not be universally indicative of how people’s brains respond.
Some people were less responsive to the intake
of milkshake, but that does not necessarily mean they would equally be less
responsive to other foods.
milkshake is not the main staple people use. This means it is not convincing to
say that people who are less responsive to milkshake would tend to eat more
foods and gain more weight.
Taq1A variant carriers have been found to have a low
number of dopamine D2 receptors, meaning the gene variant has something to do
with an individual's response to the pleasure from eating food.
More of dopamine resulting from use of food,
alcohol and illicit drugs results in a better sensation of the pleasure or joy.
But the status of the gene variant by itself does not
mean the carriers would be more likely to eat more food to compensate the
"deficiency". Studies on the issue are controversial or even
confusing and no solid conclusion has been made yet although some studies have linked
the gene variant to obesity.
David C and colleagues from the York University in
Toronto, Canada suggested that the people with who are obese or have binge
eating disorder may possess another genetic variant in addition to the Taq1A A1
allele that interacts with the A1 allele to produce higher dopamine activity.
David and colleagues noted in their study report that the
sensitivity of dopamine reward pathways has been implicated in the risk of
certain disorders such as overeating and obesity, but it was not clear whether a
Reward Deficiency Syndrome or hyper-sensitivity to reward prompt people to eat
more for the pleasure.
They found from their study that binge eating disorder
and obese subjects actually "reported greater reward sensitivity than
normal-weight controls, but only among those carrying the A1 allele."
They also found that "normal-weight controls with at
least one copy of the T allele of the C957T marker (AT or TT genotypes) had
significantly lower reward sensitivity scores than any of the other groups who
did not differ from each other."
The study was published in the April 1, 2008 issue of Progress
in Neuro-Psychopharmacology & Biological Psychiatry.
Anti-obesity drug may be developed to suppress one’s appetite
and reduce his intake of calories. But for now, those who want to control their
body weight or want to avoid becoming obese may consider doing two things:
eating a whole foods plant-based diet and doing moderate amounts of physical
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