High anxiety. Rats "addicted" to sugary food spent less time on the open parts of this maze.

Pietro Cottone

Chocolate Cake: The New Heroin?

If you're constantly starting new diets, then breaking them, you may have more in common with a drug addict than you know. A new study suggests that yo-yo dieters experience the same stressful pangs of withdrawal when they go on a diet that addicts experience when they go cold turkey.

The idea that bad food can be addictive is not new. But previous studies have tended to focus on the positive reinforcement side of the equation--for example, the pleasurable "rush" you get from eating chocolate cake. "This is just part of the story," says Pietro Cottone, a neuroscientist at Boston University and a co-author of the new study, which was conducted at The Scripps Research Institute in La Jolla, California. The brain also has a negative reinforcement system that causes anxiety and stress during withdrawal. Rather than doing drugs for the rush, he says, addicts do drugs to relieve the stress associated with withdrawal. Dieters often follow the same pattern of abstinence and relapse as drug addicts, so Cottone and his colleagues wanted to see whether the same brain circuitry might be involved.

The researchers gave one group of rats unlimited access to regular rat food for 5 days, followed by 2 days of sugary, chocolate-flavored rat chow. ("They like it a lot," says Cottone.) The team repeated this cycle for 7 weeks and compared the rats' food intake and behavior with that of a control group of rats that had access only to standard chow.

The control rats ate roughly the same amount of food every day, but the rats in the experimental group did not: When the junk food arrived, they pigged out. By the fifth week, the experimental rats were eating roughly 20% more food when they had access to chocolate chow than rats in the control group ate. And when it was replaced with normal food, they ate less normal food, approximately 30% less by week 5. As the study progressed, the effect became stronger. What's more, the rats going through chocolate-chow withdrawal spent less time in the exposed parts of a specially designed maze, a measure of increased anxiety. When the chocolate chow was returned, the anxiety disappeared.

The researchers suspected that the anxiety was the result of corticotropin-releasing factor (CRF), a hormone involved in the brain's stress response. Previous studies have shown that this molecule plays a role in drug and alcohol withdrawal. Indeed, when the researchers gave the rats a drug to block their CRF receptors, the animals ate less chocolate chow and more normal chow. They also experienced less withdrawal-associated anxiety. Further experiments revealed that the rats expressed five times more CRF during their withdrawal periods than during their binge periods.

This is the first time the CRF system has been implicated in food addiction, offering a potential drug target, the team reports online today in the Proceedings of the National Academy of Sciences. Drugs to block CRF receptors in the brain are currently being developed.

"This is a brilliant study," says Markus Heilig, a psychiatrist at the National Institute on Alcohol Abuse and Alcoholism in Bethesda, Maryland, who has studied the role of CRF in alcohol addiction. "[Intermittent] dieting is not a good idea, this would seem to indicate." In fact, Heilig says, the study suggests that long-term serial dieting may be driving the biology of the brain into a state in which an individual will experience increased cravings for junk food. Whether you're talking about alcohol, drugs, or even junk food, he says, the more times you relapse, the more stress you feel during withdrawal, and the harder it is to stay on the wagon. "That is the vicious circle," says Heilig.