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Unhealthy foods often seem addictive. In fact, new research shows that sweet or fatty foods can act a lot like a drug in the brain. NPR's Jon Hamilton has that story.

JON HAMILTON: If you've ever wondered why it's hard to stay on a diet, consider this observation from�Ralph DiLeone, a brain scientist at Yale.

Dr. RALPH DILEONE (Yale): The motivation to take cocaine, in the case of a drug addict, is probably engaging similar circuits that the motivation to eat is in a hungry person.

HAMILTON: DiLeone says that's what brain scientists have concluded after comparing studies of overeating with studies of drug addiction. He says those studies show that the wiring in our brains include special pathways that make us feel good when we eat - and really good when we eat sweet or fatty foods with lots of calories.

Dr. DILEONE: Drug addiction is really usurping or taking over - hijack is what we usually say - some of these pathways that evolved to promote food intake for survival reasons.

HAMILTON: DiLeone says that doesn't necessarily mean food is addictive the way cocaine is. But he says there's growing evidence that eating a lot of certain foods early in life can alter your brain.

Teresa Reyes, of the University of Pennsylvania, showed that in an�experiment with mice.

Ms. TERESA REYES (University of Pennsylvania): We gave mice a high-fat diet from the time that they were weaned until the time we studied them, which was at 20 weeks of age. And in that time, they gained significant amounts of weight and became obese.

HAMILTON: Then Reyes and her team looked at the brain's pleasure centers -areas known to change in drug addiction.

Ms. REYES: And what we found is that in animals that were obese, there were really dramatic changes in these areas of the brain that participate in telling us how rewarding food is.

HAMILTON: The changes made these areas less responsive to fatty foods, so an obese mouse would have to eat more fat than a typical mouse to get the same amount of pleasure. And Reyes says some of the changes didn't go away, even when the mice returned to a normal diet.

Ms. REYES: So it is similar to what happens in cases of chronic drug abuse. The reward circuitry changes in a similar way, and that promotes the seeking of that drug - or in our case, in seeking palatable food.

HAMILTON: Reyes says that could help explain why obese children tend to remain that way as adults.

More evidence of a link between food and drugs comes from a team that has been trying to understand how hunger can trigger an animal's craving for drugs.

Mr. URI SHALEV (Researcher, Concordia University): Hungry animals will take a lot of drugs.

HAMILTON: Uri Shalev is a researcher at Concordia University in Montreal. He and his colleagues�studied rats�that had learned to give themselves heroin by pressing a lever. When the scientists removed the heroin, the rats mostly stopped pressing the lever. But when the scientists also took away the rats' food, the lever pressing came back with a vengeance.

Mr. SHALEV: Even though they don't get the drug anymore, but they will go and they'll press the lever and then, this could be like hundreds of times.

HAMILTON: Shalev's team thought this behavior might involve a substance in the brain called neuropeptide Y. It makes animals feel hungry. And sure enough, when hungry rats got a substance that blocks neuropeptide Y, they stopped pressing the lever.

Plenty of other studies also have shown links between food and drugs. A Swedish team found that a stomach hormone called ghrelin could make rats seek sugar the way addicts seek drugs. And a team at the University of California-Santa Barbara found that male rats chose sugar over small amounts of cocaine, while female rats did just the opposite.

Even so, Ralph DiLeone, from Yale, says it's still not clear how far the food-drug comparison holds up, especially in people.

Dr. DILEONE: There's an ongoing argument in my field whether food's addictive or not. Something to keep in mind is whether it's addictive or not, there's probably components that are similar to addiction. And in the end, we probably have to use that information to try to deal with this problem.

HAMILTON: DiLeone says that almost certainly means focusing on eating behavior early in life. He says it also could mean taking approaches used to treat addiction, and adapting them to overeating.

Jon Hamilton, NPR News.

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