New research has revealed that an energy-burning form of fat is active in adults—a finding which may open new avenues for efforts to combat obesity, a strong risk factor for type 2 diabetes. Unlike “white fat,” which stores energy and comprises most body fat, another type of fat, called “brown fat,” burns calories to help keep animals warm. In humans, it has been thought that brown fat is active only in babies and children. Now, using advanced imaging technology (PET-CT scans), a new study has found evidence that a significant portion of adults retain metabolically active brown fat. In this study, researchers detected substantial amounts of active brown fat in the neck region of adults. They also found some key differences among people. Older people tended to have less brown fat, but being thinner was associated more with having brown fat, especially among older people—suggesting that brown fat may help protect against age-related weight gain. Interestingly, the researchers also observed that a person’s brown fat changed with the outdoor temperature, with the most brown fat activity detectable in colder weather. This finding is consistent with two other research studies (funded in Europe) that were published at the same time, which showed that brown fat activity increased in people briefly exposed to cold. These clinical findings dovetail with recent insights in animal models into the molecular signals controlling the growth of brown fat. Together, these discoveries may help scientists develop therapeutic drug interventions to promote weight loss through increasing brown fat, or to exploit the finding that brown fat is activated by exposure to cold temperatures.
Cypess AM, Lehman S, Williams G, Tal I, Rodman D, Goldfine AB, Kuo FC, Palmer EL, Tseng YH, Doria A, Kolodny GM, and Kahn CR: Identification and importance of brown adipose tissue in adult humans. N Engl J Med 360:1509-17, 2009.