Laura Sanders follows up on a story first reported from the Society for Neuroscience’s 2009 meeting

By Laura Sanders

Web edition: March 29, 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 (or, in journal geekspeak, “palatable energy-dense food readily available for human consumption”) behaved like addicts — they got their junk food fix even when it meant enduring a painful shock.

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.

The news should come as no surprise to many of us, especially junk food ad execs. The study reinforces what the commercials told me all along — I really can’t eat just one. (I also can’t believe I ate the whole thing.)

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.”