Scientists say they have found a way to turn body fat into a better type of fat that burns off calories and weight.

The US Johns Hopkins team made the breakthrough in rats but believe the same could be done in humans, offering the hope of a new way to treat obesity.

Modifying the expression of a protein linked to appetite not only reduced the animals' calorie intake and weight, but also transformed their fat composition.

"Bad" white fat became "good" brown fat, Cell Metabolism journal reports.

Brown fat is abundant in babies, which they use as a power source to generate body heat, expending calories at the same time.

But as we age our brown fat largely disappears and gets replaced by "bad" white fat, which typically sits as a spare tyre around the waist.

Experts have reasoned that stimulating the body to make more brown fat rather than white fat could be a helpful way to control weight and prevent obesity and its related health problems like type 2 diabetes.
Novel approach

Various teams have been searching for a way to do this, and Dr Sheng Bi and colleagues at the Johns Hopkins University School of Medicine believe they may have cracked it.

They designed an experiment to see if suppressing an appetite-stimulating protein called NPY would decrease body weight in rats.

When they silenced NPY in the brains of the rodents they found their appetite and food intake decreased.

Even when the rats were fed a very rich, high-fat diet they still managed to keep more weight off than rats who had fully functioning NPY.

The scientists then checked the fat composition of the rats and found an interesting change had occurred.

In the rats with silenced NPY expression, some of the bad white fat had been replaced with good brown fat.

The researchers are hopeful that it may be possible to achieve the same effect in people by injecting brown fat stem cells under the skin to burn white fat and stimulate weight loss.

Dr Bi said: "If we could get the human body to turn bad fat into good fat that burns calories instead of storing them, we could add a serious new tool to tackle the obesity epidemic.

"Only future research will tell us if that is possible."

Dr Jeremy Tomlinson, an expert at the University of Birmingham's Centre for Obesity Research, said: "This is exciting, novel and interesting.

"We will need a lot more work to tease this out, but it could offer a feasible way to develop new treatments for obesity."