This past winter, vests were a hot button issue thanks to then US presidential hopeful Rick Santorum. But a vest that cools—rather than warms—could fire up studies of brown fat as researchers seek drugs that turn on this calorie-burning tissue.
Compared with white fat, which mostly acts as an energy repository, brown fat serves to generate heat. In the past, researchers believed only babies made use of brown adipose tissue. Now we know adults have small deposits of brown fat throughout the body that burn energy only in chilly environments. With roughly two-thirds of the US classified as overweight, researchers are keen on pinpointing how brown fat is activated and how to convert white fat to its healthier cousin to help people slim down.
In February, Canadian researchers published a study in the Journal of Clinical Investigation that looked beyond brown fat’s heat-producing capabilities to how, once activated, it affects our metabolism. With a sample size of six healthy men, they reduced average skin temperature by about 4 degrees to roughly 30°C by fitting them in a cooling suit. Positron-emission tomography (PET) allowed scientists to see for the first time that cold exposure increased the amount of nonesterified fatty acids (NEFA)—the primary source of energy for tissues in fasting conditions—in the blood stream by one-third. Despite the small sample size, researchers expressed confidence in their results due to consistent measurements across the participants.
But it would be more convenient for overweight individuals to take a drug that causes brown fat to burn calories. A study published this week in the Proceedings of the National Academy of Sciences (PNAS) set out to test a possible drug therapy. Aaron Cypess of the Joslin Diabetes Center in Boston and his team wanted to determine if an ingredient found in over-the-counter decongestant drugs, called ephedrine, might activate brown fat without any cold exposure. A meta-analysis in 2003 had previously suggested that ephedrine may produce modest weight loss in humans. Ephedrine seems to cause weight loss by stimulating a release of the messenger molecule norepinephrine, thereby increasing heart rate. Brown adipose tissue has receptors for norepinephrine, so researchers reasoned the drug would activate this type of fat.