Researchers have identified a drug that turns 'bad' white fat cells into 'good' muscle making white cells.
The discovery was made during research into new drugs to tackle obesity.
Brown fat cells make people burn off more calories than they store.
"If we activate brown fat, we can eat more and not gain weight," the Daily Star quoted London's Professor Sir Stephen Bloom as saying.
But he added that it would make us sweat a lot and we would be hot and thin.
Prof Domenico Accili, from Columbia University in the US, said the process ''is an appealing and therapeutic approach to staunching the obesity epidemic".
Scientists are now trying to weed out the drugs' unwanted side effects, which include bone loss, liver problems and hot flushes.