In a newly published study, scientists from The Scripps Research Institute have shown for the first time that the same molecular（分子的） mechanisms that drive people into drug addiction are behind the compulsion（强迫，强制） to overeat, pushing people into obesity. The new study, conducted by Scripps Research Associate Professor Paul J. Kenny and graduate student Paul M. Johnson, was published March 28, 2010 in an advance online edition of the journal Nature Neuroscience.

The study's startling findings received widespread publicity after a preliminary abstract was presented at a Society for Neuroscience meeting in Chicago last October. Articles heralding（通报，宣布） the new discovery appeared in news publications around the world, focusing on the point obese patients have been making for years – that, like addiction to other substances, junk food binging is extremely difficult to stop.

The study goes significantly further than the abstract, however, demonstrating clearly that in rat models the development of obesity coincides with a progressively deteriorating（退化，恶化） chemical balance in reward brain circuitries. As these pleasure centers in the brain become less and less responsive, rats quickly develop compulsive overeating habits, consuming larger quantities of high-calorie, high-fat foods until they become obese（肥胖的） . The very same changes occur in the brains of rats that overconsume cocaine or heroin, and are thought to play an important role in the development of compulsive drug use.

Kenny, a scientist at Scripps Research's Florida campus, said that the study, which took nearly three years to complete, confirms the "addictive" properties（属性，性能） of junk food.

"The new study, unlike our preliminary abstract, explains what happens in the brain of these animals when they have easy access to high-calorie, high-fat food," said Kenny. "It presents the most thorough and compelling evidence that drug addiction and obesity are based on the same underlying neurobiological（神经生物学的） mechanisms. In the study, the animals completely lost control over their eating behavior, the primary hallmark（品质证明，特点） of addiction. They continued to overeat even when they anticipated receiving electric shocks, highlighting just how motivated they were to consume the palatable（美味的，可口的） food."

The scientists fed the rats a diet modeled after the type that contributes to human obesity—easy-to-obtain high-calorie, high-fat foods like sausage, bacon, and cheesecake. Soon after the experiments began, the animals began to bulk up（增重，养胖） dramatically.

"They always went for the worst types of food," Kenny said, "and as a result, they took in twice the calories as the control rats. When we removed the junk food and tried to put them on a nutritious diet – what we called the 'salad bar option' – they simply refused to eat. The change in their diet preference was so great that they basically starved themselves for two weeks after they were cut off from junk food. It was the animals that showed the "crash" in brain reward circuitries that had the most profound shift in food preference to the palatable, unhealthy diet. These same rats were also those that kept on eating even when they anticipated being shocked."