Once considered an inert tissue, fat—or adipose tissue—is now known to play an active role in the body’s critical functions by secreting hormones that regulate hunger and body temperature. Body fat comes in several varieties; for example, white adipose tissue stores excess energy, and brown adipose tissue primarily burns energy. In the last decade, researchers have isolated a new kind of fat tissue called beige adipose tissue. Beige fat cells begin life as white fat cells but take on the features of energy-burning brown fat cells under certain circumstances.