NEW ORLEANS--People who consider sweets addictive will sympathize with rats fed sugary meals. The rats suffered withdrawal symptoms when researchers blocked a part of the brain that responds to drugs such as morphine or heroin, suggesting that sugar is acting on the brain in much the same way. People with eating disorders might have similar symptoms of addiction, the researchers say.
The brain's opioid system registers the intense pleasure that comes from taking morphine, but it also responds more mildly to the body's own opioids. These substances are released, for instance, when you eat delicious foods.
While preparing rats for an unrelated study, then-undergraduate Carlo Colantuoni noticed that rats given a high-sugar diet got agitated before feeding time. He and his advisor, psychologist Bartley Hoebel of Princeton University, found that if they deprived rats of food for half the day and then gave them sugar water, the rats binged on their food. Much like a drug addict craving ever-bigger doses, the animals ate more and more sugar water at the beginning of their feeding cycle.
To test whether the rats showed a major sign of addiction, withdrawal, the researchers blocked their opioid system with naloxone. The rats who had been binging on sugar water responded as if they were addicted to morphine, reported Colantuoni, now a grad student at Johns Hopkins University, here 7 November at the Society for Neuroscience's annual meeting. The rats were anxious, agitated, and they chattered their teeth. Rats fed bland lab chow, in contrast, weren't bothered by the naloxone.
Hoebel cautions that withdrawal is just one sign--and not proof--of addiction, but he and Colantuoni point out that people with bulimia nervosa also fast and then binge, possibly activating similar, potentially addictive brain responses. That's a "reasonable extension" of the research, says behavioral neuroscientist Ann Kelley of the Wisconsin Psychiatric Institute in Madison, who says that it might help explain why everyone from Epicureans to beagles love tasty foods.