Not only are fat people cursed with less physical attractiveness, greater health risks, and greater difficulty in getting around. Obese people get less pleasure out of eating food.
AUSTIN, Texas—Obese individuals may overeat because they experience less satisfaction from eating food due to a reduced response in their brains' reward circuitry, according to a new study by Eric Stice, psychology researcher at The University of Texas at Austin.
While eating, the body releases dopamine, a neurotransmitter in the reward centers of the brain, but 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 signaling in the brain's reward circuitry.
Stice and a team of researchers have published their findings in the Science article, "Relation Between Obesity and Blunted Striatal Response to Food is Moderated by TaqIA A1 Allele."
A genetic variation that lowers the number of dopamine neurotransmitter receptors reduces one's ability to enjoy a chocolate milkshake. Nature is cruel. Some people have a handicapped ability to excite their brain's dorsal striatum.
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.
So if you are skinny you probably can better enjoy food than fat people can.
So the overweight aren't overweight because they've enjoyed food more. They are overweight because they need more stimulation to feel pleasure from food.
The results, drawn from two studies using functional magnetic resonance imaging (fMRI) at the University of Oregon's Lewis Center for Neuroimaging, appear in the Oct. 17 issue of the journal Science. The first-of-its-kind approach unveiled blunted activation in the brain's dorsal stratium when subjects were given milkshakes, which may reflect less-than-normal dopamine output.
"Although recent findings suggested that obese individuals may experience less pleasure when eating, and therefore eat more to compensate, this is the first prospective evidence for this relationship," said Eric Stice, lead author and senior researcher at the Oregon Research Institute (ORI) in Eugene. "The evidence of temporal precedence suggests it is a true vulnerability factor that predates obesity onset. In addition, the evidence that this relation is even stronger for individuals at genetic risk for compromised signaling in these brain regions points to an important biological factor that appears to increase risk for obesity onset."
The researchers focused on a variant of the TaqlA1 gene, which is associated with increased body mass as well as a reduction of dopamine signaling in the dorsal striatum. The blunted response to tasty food was particularly pronounced in women with the variant. In addition, women with the variant were much more likely to gain weight after a year.
Prior work had shown that obese people tend to have fewer dopamine receptors in the brain and suggested that they overeat to compensate for this reward deficit. The current findings are consistent with the theory that the blunted response to food represents a vulnerability factor for obesity but it does not conclusively rule out the possibility that the finding reflects an adaptation to over-eating, Small cautioned.
How wide ranging is this genetically caused diminished capacity for pleasure? Does it reduce pleasure from most aspects of life?
Using Functional Magnetic Resonance Imaging (fMRI), Stice’s team measured the extent to which a certain area of the brain (the dorsal striatum) was activated in response to the individual’s receipt of a taste of chocolate milkshake (versus a tasteless solution). Participants in the studies were also tested for the presence of a genetic variation linked to a lower number of dopamine D2 receptors, the Taq1A1 allele. Researchers tracked participants’ changes in body mass index (BMI) over a 1-year follow up. Results showed that those participants with decreased striatal activation in response to milkshake receipt and those with the A1 allele were more likely to gain weight over time.
“These results suggest that individuals with hypofunctioning reward circuitry are at increased risk for unhealthy weight gain,” said Stice. “Thus, it is possible that behavioral or pharmacological interventions that correct this reward deficit may help prevent and treat obesity – an avenue we are currently pursuing in our research.”
This puts a whole new spin on the idea of "appetite for life". You'll be healthier if you can get more enjoyment from less experience.
Imagine a future treatment for obesity: Gene therapy or stem cell therapy that increases your concentration of dopamine D2 receptors in the dorsal striatum of the brain. Such a therapy would alter how a person experiences life.
|Share |||Randall Parker, 2008 October 16 10:39 PM Brain Appetite|