After being injected with an opiate-like chemical produced in the human brain, laboratory rats ate twice the normal amount of sweet fatty food. (Photo: Alexandra Difeliceantonio)

Are you on a diet but  having a hard time resisting that candy bar or cheeseburger?  The problem  might really be in your head.

Researchers have found that an opium-like chemical produced in the brain might explain why some people overeat sweet and fatty foods.

“This means that the brain has more extensive systems to make individuals want to over consume rewards than previously thought,” says Alexandra DiFeliceantonio of the University of Michigan, Ann Arbor, who led the study. “It may be one reason why over-consumption is a problem today.”

The researchers found  a region of the brain called the neostriatum, located near the middle and front of the brain, which is best known for  controlling motor movements. It also produces the opiate-like chemical called enkephalin, which  DiFeliceantonio says sparks and intensifies the urge to consume pleasant rewards.

To make their findings, DiFeliceantonio and her team injected some of the morphine-like drug directly into the neostriatum of their lab rats.  After the injections, the rats were fed candy-coated chocolate. The rodent test subjects ate more than twice the number of chocolates than they would normally have eaten.

The researchers also found the levels of enkephalin – the opium-like chemical manufactured by the neostriatum – surged when the rats began to eat the  candy. And while the enkephalins, or comparable drugs, didn’t actually make the rats enjoy the candy more, they did increase their cravings and compulsion to eat them.

“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.”

DiFeliceantonio says the findings  reveal a lot about our tendency to binge and could eventually lead to the development a drug that  blocks the impulse to overeat.