Junk food junkies

Chowing down on junk food makes rats act like heroin addicts.

By Jessica A. KnoblauchFri, Oct 23 2009 at 2:10 PM EST

Photo: ZUMA Press

Put down that cookie and read this.

According to a recent study presented at the Society for Neuroscience’s annual meeting in October, rats that are given unlimited amounts of junk food had similar addictive behaviors to rats addicted to heroin.

“This is the most complete evidence to date that suggests obesity and drug addiction have common neurobiological underpinnings,” explained study coauthor Paul Johnson of the Scripps Research Institute to ScienceNews.

The reason is that the pleasure centers in the brains of rats became less responsive as the rats continued to binge on high-fat, high-calorie foods. Much like heroin addicts, the rats had to consume more and more of the addictive substance just to get a sugar high.

“They lose control,” said coauthor Paul Kenny. “This is the hallmark of addiction.”

To see how this works, the researchers fed the rats either entirely healthy diets or entirely unhealthy diets. The junk food diets consisted of foods like bacon and cheesecake.

Not surprisingly, the rats that ate the junk food diet soon developed compulsive eating habits and became obese.

What's surprising is that the addiction to junk food was so strong that the rats were willing to get shocked in the foot just to get more junk food. Talk about motivation!

Though the rats that didn’t get the junk food in the beginning quickly stopped eating the high-fat food once they got shocked, the foot shock didn’t faze rats already accustomed to the junk food. They just kept on eating, in spite of the oncoming shock.

“What we have are these core features of addiction, and these animals are hitting each one of these features,” Kenny explained.

Even weeks after the rats were off of the junk food diet, the researchers found that the “reward pathway deficits” still persisted, which shows just how difficult it is to give something up once you’ve become addicted to it in the past.

“It’s almost as if you break these things, it’s very, very hard to go back to the way things were before,” Kenny says.

Even when there was only a choice between healthy food and no food at all, the rats chose the no food option.

“They starve themselves for two weeks afterward,” Kenny said. “Their dietary preferences are dramatically shifted.”

Of course, the real significance of the study is not whether fat rats can become addicted to candy and cookies, but rather what the effects of eating these types of foods over the long term might have on the reward system.

“We might not see it when we look at the animal,” says obesity expert Ralph DiLeone of Yale University School of Medicine. “They might be a normal weight, but how they respond to food in the future may be permanently altered.”