That is because one of the other studies found that PET/CT can detect much more brown fat if people are in a room cooled to 61?°F. Likewise, Cypess and his colleagues found that people who underwent PET/CT in the winter had more brown fat activity than those scanned in the summer.

They also discovered that brown fat is most abundant in young women and least frequent in older, overweight men. In fact, women were more than twice as likely as men to have substantial amounts of brown fat.

"One theory for this is that women may have less muscle mass overall, so they need more brown fat to generate heat and keep warm," Cypess said.

Brown fat provides a new focus for developing treatments protecting against obesity and its complications, according to Cypess. However, it may not be enough to lose weight to just have brown fat. The researcher said, "We may have to turn it on and make sure it burns calories in a regulated, safe manner."

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