Overweight women may overeat because the reward centres in their brains seem to respond less to a chemical called dopamine, according to researchers from Texas, Oregon.
Dopamine is the main neurotransmitter involved in the brain's reward pathways. Eating food is associated with releasing dopamine, and the more that's released, the greater the degree of pleasure.
In this new study, functional magnetic resonance imaging (MRI) was used to measure brain responses in 53 female university students and 33 teenage girls as they drank squirts of a chocolate milkshake or a tasteless solution for comparison. Body mass index was tracked for one year after the women's brain responses to the milkshake were determined.
After one year, the young women who showed less dopamine brain activation in response to the milkshake had an increase in their BMI that was not seen in their peers who had a greater response to dopamine released after drinking the delicious shake.
These findings suggest people with fewer dopamine receptors need to eat more of a tasty food to experience the same level of pleasure as other people.
Dopamine also affects our ability to control impulses. Therefore, it's also possible that people with fewer dopamine receptors may overeat as an impulse, further increasing their risk becoming obese, says the study author.
Learning more about the linked between brain chemicals like dopamine and weight gain can lead to new treatments and new methods of promoting behavior change in those who are more suspectable to overeating.
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This study was published in the journal Science on October 17, 2008.
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