Dopamine Linked to Junk Food Addiction
Junk food is truly addictive in the clinical sense — it changes the way the brain processes the neurotransmitter dopamine. This makes junk food addiction similar to cocaine and heroin addictions, according to recent research conducted at the Scripps Institute in Florida.
In a recent study by Professor Paul J. Kenny, rats were fed either a healthy diet or a junk food diet consisting of sausage, bacon, pound cake, cheesecake, chocolate and frosting. Mice in the junk food group were divided into two groups – one group had access to junk food all day every day, while the other group was allowed to binge on junk food, but only for one hour per day, according to the paper in Nature Neuroscience.
Rats in the group with unlimited access to junk food became compulsive overeaters, gaining about twice as much weight as rats in the other two groups. Even worse, these rats continued to compulsively gorge on junk food, even when they were punished for doing so. For these rats, the positive effects of satisfying their addiction to junk food outweighed the negative consequences, even the threat of electric shock.
Kenny and his associate Paul M. Johnson compare the rat’s behavior to that of overweight humans, who continue to overeat junk food even when faced with negative consequences such as ridicule, low self-esteem and the physical limitations of obesity.
The rats consistently chose the worst available food. When they were put on healthy food – the researchers called it the “salad bar option” the overweight rats simply refused to eat at all, for two weeks.
The researchers found that the rats had significant reduction in the density of D2 dopamine receptors in the brain – a biochemical change similar to that encountered in rats addicted to drugs. The D2 receptor is especially important because it helps control impulsive behavior.
Dopamine is a neurotransmitter that occurs naturally in the brain. A variety of stimuli produce dopamine including food and sex. Drugs including nicotine, amphetamines and cocaine are pleasurable because they cause the release of dopamine.
When the pleasure centers of the brain are over stimulated, they become less and less sensitive. The deteriorating chemical balance in the reward centers requires greater amounts of the drug to feel good and eventually large amounts of the drug simply to feel normal. The only difference is that in this study, the drug of choice was not heroin or cocaine. It was junk food.
Many earlier studies linked dopamine receptor problems with alcoholism. Previous research linked a certain allele of the D-4 dopamine receptor gene with addictive behaviors including alcoholism, cocaine addiction, obesity and compulsive overeating.
By Joni Holderman, [email protected], contributing reporter for Mental Health News.