Brown Fat Revelations May Lead to New Weight Loss Drugs

"Five years ago this February, Aaron Cypess had an epiphany about fat. A fellow in endocrinology at Boston’s Beth Israel Deaconess Medical Center, Cypess happened to be attending a lecture in which a doctor presented images of human PET scans. At one point, Cypess recalls, the doctor indicated an area corresponding to the neck and said, rather dismissively, “Oh, that’s brown fat.” Cypess was taken aback. After the lecture, he approached the doctor and told him he must have been mistaken: Everyone knows there’s no brown fat in human adults. The doctor responded, “Yeah, there is. We see it all the time.” Cypess paused. “Wait a minute,” he said. “Really?”

Brown fat has long been known to exist in infants and animals such as mice, but until recently scientists thought it disappeared before human adulthood, leaving only the white fat that’s associated with weight gain. Unlike white fat, which stores energy, chestnut-colored brown fat burns it. Brown fat cells contain a large supply of organelles called mitochondria, and an enzyme that allows them to release energy from food calories directly as heat. This spring, multiple studies in The New England Journal of Medicine—including one co-authored by Cypess, now a research associate at the Joslin Diabetes Center in Boston—confirmed that not only is brown fat common in adults, it’s also important to metabolism: Younger, thinner people have more detectable brown fat than their older, pudgier counterparts...

Animal studies also suggest brown fat boosts weight loss. Last year, Stockholm University scientists found that mice that could not make brown fat gained weight 50 percent faster than mice that could. In a 2008 study, mice fed a high-fat diet and kept at room temperature ended up nearly four times heavier than mice fed the same diet and housed at 39 F."