Scientifically, obesity is characterized by an increase in adipose tissue – what most people call fat. Mammals, including humans, have two different kinds of adipose tissue in their bodies. White adipose tissue, or white fat, is where energy is stored; brown adipose tissue, or brown fat, plays an important role in a body’s heat production through burning off fat (energy expenditure). Because these functions are all vital to survival, fat tissue is an important part of any body. However, as one grows from baby to adult, brown adipose tissue in the body gradually disappears or loses activity, and then the problem comes in when too much white fat accumulates in the body.