A switch in the brain that regulates when fat is burned or stored is always on in obese people, new research shows.

Obese people aren't able to regulate the way body fat is stored or burned because a "switch" in their brain stays on all the time, a new study has shown.

In most cases specialised fat cells called adipocytes are switched back-and-forth from brown, which are energy burning, to white, which store energy.

The study, published on Wednesday in Cell Metabolism, showed that after a meal the brain responds to insulin when sugars spike, by sending signals to promote the browning of fat to expend energy.

Then, after a fast, the brain instructs these browned cells to convert back to white adipocytes, again storing energy.

The brain's ability to sense insulin and co-ordinate feeding with burning energy is controlled by a switch-like mechanism, researchers from the Metabolic Disease and Obesity Program at Monash University say.

"What happens in the context of obesity is that the switch stays on all the time - it doesn't turn on off during feeding," lead researcher Professor Tony Tiganis said.

"As a consequence, browning is turned off all the time and energy expenditure is decreased all the time, so when you eat, you don't see a commensurate increase in energy expenditure - and that promotes weight gain," Professor Tiganis said.

Researchers are now exploring the possibility of inhibiting the switch to aid weight loss, but they say any therapy is "a long way off".