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See Inside April/May 2008

Sweeter Than Cocaine

Rats prefer a sugary drink to drugs

If the alarming statistics surrounding the so-called obesity epidemic have not convinced you of the dangers of a sugar-packed diet, a new study might have you thinking twice. Rats given a choice between highly sweetened water and intravenous cocaine overwhelmingly favored the tasty beverage. Their preference was just as intense whether the drink was sweetened with saccharin or sugar.

This finding, reported recently by graduate student Magalie Lenoir and her colleagues at the University of Bordeaux in France, fuels growing suspicions that for some people sweets could be as pleasurable and addictive as habit-forming drugs. As the theory goes, our hypersensitivity to sweet taste evolved when sugar was scarce and an indicator of a high-energy meal. Excessive sugar in today’s diets may overstimulate the sweet receptors in the brain, leading to a loss of self-control mechanisms and the risk of addiction.

Indeed, drugs and food activate similar reward pathways in the brain. A separate recent study showed that rats can become dependent on sugar, exhibiting typical symptoms of addiction, including craving and both behavioral and neurochemical signs of withdrawal.

The bigger surprise, notes Serge Ahmed, who designed the preference experiment, is that rats that were already experienced cocaine “users” (they had learned to self-administer cocaine) still opted for sweetened water over the drug.

Ahmed is reluctant to generalize these results to humans just yet; rather than proving that sweets are more addictive than cocaine, his team might have discovered that rats simply cannot become addicted to drugs. This explanation, Ahmed believes, would nonetheless have important implications, suggesting that researchers should focus on the prefrontal cortex and other more recently evolved brain areas found in humans and other primates.

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