Fun and friendship may be among the secrets of staying slim, new research has suggested.
Studies of mice showed that living in a dynamic social environment caused them to generate a healthy type of fat that burns up calories.
Scientists believe the same process probably occurs in humans. Conversely, living a "couch potato" existence that replaces real-life interactions with TV and the internet could be contributing to obesity, they said.
Harmful fat is the "white" variety that acts as an energy store and leads to bulging waistlines.
However healthy "brown" fat helps keep bodies lean by burning calories to generate heat.
Growing babies have relatively large amounts of brown fat, while adults have very little. However, scientists know that adults can increase their levels of brown fat through exposure to cold, or the stimulation of certain nerves.
Study leader Professor Matthew During, from Ohio State University in Columbus, US, said: "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.
"Our findings suggest that we can potentially induce this transformation by modifying our lifestyle or by pharmacologically activating this brain-fat pathway."
Exercise alone could not account for the changes seen in the mice, according to the study published in the journal Cell Metabolism.
"I'm still amazed at the degree of fat loss that occurs," Prof During added. "The amount of fat that comes off is far more than you would get with a treadmill."
