Brain pleasure centers became progressively less responsive in rats fed a diet of high-fat, high-calorie food, a new study has found. As the changes occurred, the rats developed compulsive overeating habits -- and became obese. The overeating continued even when it meant the rats had to endure an unpleasant consequence (a mild foot shock) in order to consume the food.

The findings were presented at Neuroscience 2009, the annual meeting of the Society for Neuroscience and the world's largest source of emerging news about brain science and health.

The researchers also found that as the activity of the brain's pleasure centers decreased, the rats became less likely to eat a well-balanced, nutritious diet -- even when the less palatable healthy food was the only food available to them.

"Not only did we find that the animals' brain reward circuits became less responsive as they continued to overeat and become obese," said senior author Paul J. Kenny, PhD, of the Scripps Research Institute in Jupiter, Fla., "but that decrease in responsiveness was similar to what our laboratory has seen previously in rats as they become addicted to cocaine or heroin. The data suggest that obesity and addiction may result from common neuroadaptations," he said.

The finding may have implications for humans, as the diets fed the rats (unlimited access to such high-caloric foods as bacon, sausage, cheesecake, and chocolate) were similar to those of millions of people who live in developed countries. Such diets are considered a major contributing factor to the current obesity epidemic in the United States.

Research was supported by Bank of America, the National Institute on Drug Abuse, and The Landenberger Foundation.