Over the last few decades the incidence and prevalence of obesity has become epidemic throughout the world. Why have we seen the swift emergence of this disease? To understand the complexity of the problem, it's necessary to appreciate the concept of "energy balance". 1 e amount of energy entering the body (as carbohydrate, fat or protein) is used to supply all tissues and organs with metabolizable fuel, or is stored in the form of fat in adipose cells, glycogen in the liver, or protein, or, lastly, is excreted as unabsorbed energy.