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Dopamine is a neurotransmitter; that is, a molecule that carries messages between neurons in your brain. It's a feel-good neurotransmitter that makes you think "I want that! I'm going to get it! And wow, that was great!"
The more dopamine you secrete in response to an activity, the more quickly you feel rewarded by that activity. If you don't secrete much dopamine in response to a rewarding activity, you have to go at the activity more vigorously in order to squeeze out enough dopamine to make you feel rewarded.
Researchers from the University of Buffalo, NY, recently studied the connection between dopamine and overeating, and they found that people who have genetically lower dopamine are more motivated to eat and that they eat more.
First the researchers tested 29 obese adults and 45 non-obese adults to see whether they had a copy of the Taq1 A1 allele, a gene that codes for fewer dopamine receptors. About half the population carries one A1 allele and one A2 allele, and nearly everyone else carries two copies of the A2 allele.
Two copies of the A2 allele give you more dopamine receptors, so it's easier for you to experience reward. If you're stuck with a copy of the A1 allele, however, you end up with fewer dopamine receptors. As a result, you need to consume more of a rewarding substance, such as food, to get the same good feeling you'd get more quickly if you had two copies of the A2 allele.
The researchers conducted two behavioral tests to assess both the reinforcing power of food and the pleasure people get from food. One test measured how much food participants ate when it was right in front of them. The second test measured how hard people would work for food, or its "reinforcing power," by testing whether they'd rather earn points to read a newspaper or to eat their favorite food.
The researchers found that both obesity and a copy of the A1 allele were associated with a significantly stronger response to food's reinforcing power; that is, how hard people would work to get the food. There were also three levels of food consumption: people who didn't find food all that rewarding regardless of their genotype ate the least; people who preferred to work for food but didn't have the A1 allele came second; people who were high in food reinforcement and also had the A1 allele ate the most. The theory is that they had to eat more in order to force their paltry number of dopamine receptors into action to produce that feeling of reward.
The same researchers have previously found that chemically manipulating dopamine levels alters eating behavior in overweight men, which leads them to believe that drugs might eventually help prevent obesity. On the other hand, they emphasize that behavior and biology interact and that the A1 gene doesn't necessarily cause obesity, but may contribute to it.
Source: EurekAlert, October 2007
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