Scientists have discovered a biological switch that gives energy-storing white fat the characteristics of energy-burning brown fat. The findings could lead to new strategies for treating obesity¹. The animal study by researchers at The Ohio State University Medical Center shows that the change is due to the activation² of a nerve and biochemical pathway that begins in the hypothalamus（下丘脑） , an area of the brain involved in energy balance, and ends in white fat cells. This pathway, called the hypothalamic-adipocyte axis³, also induces brown-fat-like cells within masses of white fat.

The white-to-brown fat transformation⁴ occurs when animals are placed in an enriched environment, one with a variety of social and physical challenges.

The findings are published in the September issue of the journal Cell Metabolism⁵.

"One of the holy grails of obesity therapy is to understand how to switch white fat to brown fat, and this study describes a new way to do exactly that," says study leader and researcher Dr. Matthew J. During, professor of neuroscience, of neurological surgery and of molecular⁶ virology（病毒学） , immunology and medical genetics. "Our findings suggest that we can potentially induce this transformation by modifying our lifestyle or by pharmacologically activating⁷ this brain-fat pathway."

Lead and corresponding author Dr. Lei Cao, assistant professor of molecular virology, immunology and medical genetics, notes that obesity is caused by a chronic⁸ energy surplus that is stored as lipid in white fat. "Increasing the output of energy is always attractive for obesity treatment, which is why the discovery of brown fat in adult humans caused much excitement a few years ago," she says.

"However, up to now the only known approach to inducing brown fat has been through exposure to chronic cold. Our research reveals a novel way of doing this without cold exposure. We show that animals living in an enriched environment become lean and resistant⁹ to diet-induced obesity, even in the presence of unlimited¹⁰ food." In 2010, During, Cao and their colleagues showed in a paper published in the journal Cell that this enrichment effect by itself curbed¹¹ cancer growth in animals.

The current study used a similarly designed environment, with 15-20 mice housed in large containers equipped with running wheels, tunnels, huts, wood toys, a maze¹²（迷宫，迷惑） , and nesting material, in addition to unlimited food and water. Control mice were housed in groups of five in smaller, standard laboratory containers without toys but with unlimited food and water.