Lowered dopamine levels prompt obese individuals to eat more food in an attempt to achieve that "feel-good" feeling that the chemical generates, a new study suggests.

Receptors of dopamine, a chemical in the brain that is associated with pleasure, were found to be lower in obese rats, and their levels rose when food intake was restricted.

The study was conducted at the U.S. Department of Energy's Brookhaven National Laboratory. The findings are published in the journal Synapse and are now available online.

"This research corroborates brain-imaging studies conducted at Brookhaven that found decreased levels of dopamine D2 receptors in obese people compared with normal-weight people," said Brookhaven neuroscientist Panayotis Thanos, lead author of the study.

"Dopamine is one of the neurotransmitters modulating the reinforcing properties of food," reads the report.

The researchers aren't sure whether obesity leads to reduced dopamine receptor levels or whether the receptors are themselves responsible for making people obese. However, their studies show that decreasing food intake helped increase dopamine receptor sensitivity.

The researchers measured dopamine receptor levels in the brains of adolescent and young adult genetically obese rats, as well as lean rats. Half of the rats in each group were given unlimited access to food while the other half were given 70 per cent of the daily average amount of food consumed by the first group.

Researchers found that the overall number of dopamine receptors was lower in obese than in lean rats. As well, dopamine receptor levels fell with age, though this decline was slower in rats that had restricted access to food compared with those who had constant access to food.