While eating, the body releases dopamine, a neurotransmitter in the reward centres of the brain, but lead researcher Eric Stice found obese people show less activation in the striatum relative to lean people. He also found individuals with a blunted response were more likely to show unhealthy weight gain, particularly if they had a gene associated with compromised dopamine signalling in the brain's reward circuitry.
Although research has revealed biological factors play a major role in causing obesity, few studies have identified factors that increase people's risk to gain weight in the future. Stice led a research team to explore how blunted responses in the brain relate to weight gain in young females.
"The research reveals obese people may have fewer dopamine receptors, so they overeat to compensate for this reward deficit," Stice, who has studied eating disorders and obesity for almost two decades, said. "People with fewer D2 receptors need to take in more of a rewarding substance - such as food or drugs - to experience the same level of pleasure as other people."
Using Functional Magnetic Resonance Imaging (fMRI), Stice's team measured how the dorsal striatum was activated in response to the taste of a chocolate milkshake (versus a tasteless solution). The researchers also tested participants for the presence of a genetic variation linked to a lower number of dopamine D2 receptors, the Taq1A1 allele.
For one year, the researchers tracked participants' changes in body mass index. The results revealed participants with decreased striatal activation in response to the milkshake who also had the A1 allele were more likely to gain weight over time.
MEDICA.de; Source: University of Texas at Austin