A new understanding of the origins of brown fat cells - the "good" type - may lead to new treatments for obesity.

Researchers at the Dana-Farber Cancer Institute in Boston, Massachusetts, said they used a single molecular switch to turn immature muscle cells into brown fat cells - the type which burn up calories and release energy.

It suggests brown fat may be more akin to muscle cells than conventional white fat cells, which store energy.

Obese people have large stores of white fat, and researchers think if they can coax the body into making more brown fat, this might help people them lose weight.

Meanwhile, a second team from the Joslin Diabetes Centre in Boston, found a protein important for bone growth helped promote the development of brown fat tissue in mice.

Reporting in the journal Nature, the two teams said their new findings assist understanding about the origins of brown fat in contrast to conventional white fat.

Dana-Farber's Bruce Spiegelman, who worked on the research, said researchers have been trying to find the genes that turn brown fat cells on.

Dr Spiegelman said his team previously found that PRDM16, a kind of genetic switch called a gene transcription factor, appears to regulate the development of brown fat cells.

He said: "What we show in this paper is kind of a big shock. We show that brown fat is derived from a muscle-like cell, and that brown fat and white fat are completely different."

When Dr Spiegelman's team removed PRDM16 from immature brown fat cells in the lab, something strange happened.

"The dish filled up with muscle," Dr Spiegelman said. "What it means is that muscle cells are precursor cells to brown fat cells."

Previously, his team also showed that PRDM16 could turn conventional white fat cells into brown fat cells, but Dr Spiegelman thinks in living creatures, the muscle cell is a natural cell type that gives rise to brown fat cells.

His team is now looking for a drug that could chemically stimulate PRDM16 to make more brown fat cells, which would shift the metabolism into more of a fat-burning mode.

In a separate finding, a team led by Yu-Hua Tseng of the Joslin Diabetes Centre found the protein BMP-7, known for inducing bone growth, can also promote the development of brown fat cells.

When Dr Tseng's team delivered this protein into mice through a virus, the mice made more brown fat tissue. And they found mice that developed extra brown fat tissue gained less weight than other mice, suggesting a potential use in weight loss.

The researchers were also able to get mice to develop extra brown fat cells by pre-treating immature brown fat cells with BMP-7 and transplanting them into the mice.

"We hope this study can be translated into applications to help treat or prevent obesity," Dr Tseng said in a statement.

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