Word: browning
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Dates: during 2000-2009
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...Until now, only rodents and human newborns have been known to have any significant deposits of brown fat, so called because of its abnormally high concentration of dark-colored mitochondria, the engines that sustain cell activity. The primary purpose of brown fat is to regulate body temperature: the mitochondria-packed cells are designed to burn high quantities of sugar, the body's fuel, and release that energy as heat - a mechanism that newborns, fresh from the warm confines of the womb, rely on to keep them toasty...
...people age, however, the body becomes more adept at regulating temperature, so brown-fat stores shrink and white fat starts to emerge. (From a biological perspective, brown fat is also highly inefficient, since cells don't need heat to run; rather, they use ATP, another chemical produced by mitochondria.) Adults with appreciable amounts of brown fat are usually those who have certain types of cancer or hyperthyroidism, conditions that stimulate the growth of brown fat. (Read an article about how kids who lack self-control are more likely to gain weight...
...Sven Enerbäck at the University of Göteborg in Sweden has shown, using the latest imaging technologies, that healthy adults retain a sizable amount of brown fat in the front and back of the neck. (That was a surprise, since in rodents, the depots tend to be along the back, around the shoulder blades.) Enerbäck and his team studied five patients and confirmed, using genetic analysis, that the cells around the neck were indeed brown...
...sense, scientists have known this for years. While scanning patients with positron emission tomography (PET), an imaging technique often used on cancer patients to detect the spread of tumors, scientists have long noted the excess activity of brown-fat cells in their images. They just didn't realize what they were looking...
...Since PET picks up glucose-burning activity in cells, hot spots on PET scans of cancer patients generally indicate actively growing tumors. But after doing biopsies, doctors found that hot spots in the neck of most of their patients weren't cancerous at all. These turned out to be brown-fat deposits...