Drug fires up brown fat, ignites metabolism

'Brown fat,' seen here under a microscope, seems to be concentrated around the neck and is active in burning energy to generate heat.

A drug that's normally used to curb an overactive bladder could help unleash even more metabolic power than what brown fat is capable of under normal circumstances, says a research team hailing primarily from Boston.

Even without the drug, brown fat in the body burns energy to generate heat, unlike white fat, which stores energy and is considered the less healthy of the two fats.

"We showed that a one-time dose of the drug mirabegron stimulates human brown adipose tissue so that it consumes glucose and burns calories," says lead author Dr. Aaron Cypess, of the National Institute of Diabetes and Digestive and Kidney Diseases.

In the study, each of the 12 participants -- all of whom were healthy young men -- saw their resting metabolism soar by 203 calories per day after taking 200 milligrams of mirabegron.

Participants tolerated the dose well, according to the researchers, although it is considerably higher than the 50-milligram dose approved for those with an overactive bladder.

Mirabegron works by targeting the β3-adrenergic receptor, which is found on the cells of the bladder -- and on the surface of both brown and white fat cells.

Once the production of β3-adrenergic receptor is activated on the brown fat cells, they burn energy at higher rates, according to the study, which was published in the journal Cell Press.

Cold temperatures in the environment activate brown fat in the same way, according to a study at Maastricht University Medical Center in the Netherlands, although Dr. Cypess notes that a drug could be a more tolerable treatment.

Other projected methods to rev up metabolism sing brown fat involve creating more of it, and a study published Monday in the Federation of American Societies for Experimental Biology says each color fat can change into the other depending on the temperature.

The experiment was conducted on mice, and those looking for a metabolism boost shouldn't throw their winter coats away before it's been proven to work on humans, says Gerald Weissmann, M.D., Editor-in-Chief of the FASEB Journal.