A new brain study suggests an opium-like chemical may drive the urge to gorge on chocolate candy and similar fatty and sweet treats.

Researchers discovered this when they gave rats an artificial boost with a drug that went straight to a brain region called the neostriatum: it caused the animals to eat twice the amount of M&Ms they would otherwise have eaten.

The team also found that when the rats began to eat the chocolate-coated candies, there was a surge in enkephalin, a natural opium-like substance that is produced in the same region of the brain.

Alexandra DiFeliceantonio of the University of Michigan, Ann Arbor, in the US, and colleagues, write about their findings in a paper published online on Thursday in the journal Current Biology.

“Here, we provide evidence that enkephalin surges in an anteromedial quadrant of dorsal neostriatum contribute to generating intense consumption of palatable food,” they write, noting that:

“Endogenous >150% enkephalin surges in anterior dorsomedial neostriatum were triggered as rats began to consume palatable chocolates,” before concluding:

“These findings reveal that opioid signals in anteromedial dorsal neostriatum are able to code and cause motivation to consume sensory reward.”

Commenting on the findings to the press, DiFeliceantonio says:

“This means that the brain has more extensive systems to make individuals want to overconsume rewards than previously thought.”

“It may be one reason why overconsumption is a problem today,” she notes.

The findings uncover a surprising role for the neostriatum, which until now has mostly been linked to movement. But there are reasons why this discovery in rats might reveal something about the human tendency for binge-eating:

“The same brain area we tested here is active when obese people see foods and when drug addicts see drug scenes,” says DiFeliceantonio.

“It seems likely that our enkephalin findings in rats mean that this neurotransmitter may drive some forms of overconsumption and addiction in people,” she adds.

The team points out enkephalins or similar drugs may exert their effect not by increasing a liking for chocolates, only the urge to eat them: not unlike the compulsive overconsumption that characterizes disorders ranging from binge eating to drug addiction.

They now plan to investigate a related topic: what happens in the brain that makes us want to stop when we come across a fast food outlet?

Written by Catharine Paddock PhD