Eating, Pleasure, and a Chemical Called Dopamine
Eating is pleasurable and we connect all the conditions surrounding a meal with that pleasure. So colors and sounds and of course, smells, can make you remember how happy eating made you feel. A TV commercial can suddenly make you think, “Mmmm, burgers….” when you’re not even hungry.
This happiness comes from a surge of dopamine, a brain-signaling chemical associated with feelings of reward and pleasure. Interestingly, obese individuals and drug addicts often have fewer dopamine D2 receptors than most and it’s speculated that this may make both types of individuals engage in compulsive reward-seeking behaviors.
Imaging the Brain for Dopamine Receptors
To investigate neurological symptoms associated with obesity, researchers at Brookhaven National Laboratory in New York used an imaging technique (positron emission tomography or “PET”) to look at the brains of obese and non-obese subjects.
The PET scans revealed significantly lower D2 levels in the striatum of the brain in the obese subjects. The levels of D2 receptors correlated with body mass index. The higher a subject’s body mass index, the fewer D2 receptors he or she tended to have. The levels of D2 receptors did not correlate with gender or brain metabolism.
Obesity Treatments Targeting Dopamine
Consistent with this finding, drugs inhibiting dopamine receptors can lead to weight gain while those that increase dopamine concentrations (e.g., Rimonobant) decrease appetite. It’s possible that low D2 receptor levels cause obese individuals to increase their food intake to make up for the lack of stimulation of their reward centers. But it’s an open question whether the low D2 receptor levels are the cause of overeating or a result of addictive behavior. It’s also an open question whether increasing dopamine release can compensate for lower levels of dopamine receptors over the long term.
Because reward circuits are altered in some obese individuals, overeating may become an involuntary act. So there may be an extra hurdle to overcome in dieting. For example, some individuals struggling to control their food intake may also be dealing with symptoms similar to withdrawal. Unlike a drug addict who can survive without drugs, an obese person still needs to eat, so it may be particularly difficult for a “food addict” to modify his or her behavior. Drugs that reduce withdrawal symptoms may be worth studying as an option for people struggling with diets.