A cancer drug which increases calorie-burning brown fat could be a new way to help combat obesity and type 2 diabetes, scientists have found.

Bexarotene (bex) targets a protein involved in the generation of brown fat, researchers at Gladstone Institutes in the US have discovered.

But a safer, more targeted drug needs to be developed before it becomes the latest flab fighting weapon, they warn.

Senior investigator Dr Sheng Ding said: "We're very excited about the prospect of using a drug to generate brown fat in the body.

"However, while bex is very effective at creating brown fat cells, it is not a very specific drug, and there are several potential side effects that may arise from taking it.

"Our next task is to develop a safer, more targeted drug that only affects genes involved in creating brown fat."

While white fat stores energy, brown fat burns it up. Around 50 grams of brown fat can burn up to 300 calories a day, the same amount of energy stored by 50 grams of white fat.

Everyone is born with small amounts of brown fat but as people age most of it disappears.

Adults with higher amounts have a lower body mass index and by increasing brown fat by as little as 50 grams could lead up to a 10lb to 20lb weight loss over a year.

The findings, published in Cell Reports, show bex, normally used to treat an immune system cancer, acts on a protein called retinoid X receptor (RXR) which controls a network of other cellular proteins.

Activating RXR causes changes to muscle precursor cells and white fat, which ultimately converts them into brown fat-like cells.

Scientists also found when RXR was stimulated by the drug, it turned on genes needed to produce brown fat and turned off genes linked to white fat or muscle.

To test how well the drug controlled body weight, mice were fed a high-calorie diet for four weeks - but only half the animals were given the drug.

It was found that the rodents given bex had more brown fat, faster metabolisms and gained less weight compared with the mice fed the same diet but not given the drug.

Researchers say the technique, which uses cellular reprogramming, could be a new way to combat obesity and type 2 diabetes.

"Introducing brown fat is an exciting new approach to treating obesity and associated metabolic diseases, such as diabetes," said co-author Dr Baoming Nie.

"All current weight loss drugs control appetite and there is nothing on the market that targets energy expenditure.

"If we can create additional stores of brown fat and boost its function in the body, we could burn off the energy stored in white fat more easily."