Junk food turns rats into food junkies
“This is the most complete evidence to date that suggests obesity and drug addiction have common neurobiological underpinnings,” says study coauthor Paul Johnson of the Scripps Research Institute in Jupiter, Florida.Posted Apr 28, 2010
Last November, Science News reported on some exciting new data coming out of the 2009 Society for Neuroscience meeting on the eerie similarities between cocaine addiction and junk food cravings. Now, the full version of the study is out in Nature Neuroscience, showing how, to a hedonistic brain, cocaine and cheesecake might not be so different.
In the brain, junk food and drugs have some similar effects, the researchers show. Rats habituated to a diet of HoHos, bacon, cheesecake and frosting behaved like addicts — they got their junk food fix even when it meant enduring a painful shock.
What happens in addiction is lethally simple, explained Paul J. Kenny, associate professor at Scripps Research Institute, and one of the authors of the study. The reward pathways in the brain become so overstimulated that the system basically turns on itself, adapting to the new reality of addiction, whether the fix of choice is cocaine or cupcakes.
In their research, Kenny and his colleagues divided rats into three groups. The first group ate a well-balanced diet; group two had the healthy diet, as well as one-hour a day access to high-calorie foods. The last group of rats were given a healthy diet, but also had full access to high-calorie, high-fat, high-sugar foods like bacon, cheesecake and Ding Dongs. The open door policy to junk foods triggered compulsive overeating in the third group, and that quickly led to obesity. “The animals completely lost control over their eating behavior,” said Kenny. “They continued to overeat even when they anticipated receiving electric shocks.”
The dopamine receptors of the brain showed 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.
The study, said Kenny, “presents the most thorough and compelling evidence that drug addiction and obesity are based on the same underlying neurobiological mechanisms.”
The results may help explain the illogical compulsion to shave off microscopic slices of a cheesecake until — well, there’s just one little bit left, so you might as well eat that too — it’s completely gone. Each bite bathes our brains in dopamine, making us feel good. But the study points out that, as with drugs, each bite brings diminishing returns.
The most telling data came from the brains of these animals. The pleasure centers in the rats’ brains became sluggish after becoming habituated to the junky food. Caught in this vicious feedback loop, the rats needed a bigger dose of junk to get the same good feelings. The rats fed junk food had fewer receptors that respond to the feel-good brain signal dopamine as compared to the rats that ate healthful, low-cal chow.
In their paper, study authors Paul Johnson and Paul Kenny, both of the Scripps Research Institute in Jupiter, Fla., offer this food for thought: “Common hedonic mechanisms may therefore underlie obesity and drug addiction.”