The worldwide epidemic of obesity and type 2 diabetes has greatly increased 
interest in the biology and physiology of adipose tissues. Adipose (fat) cells 
are specialized for the storage of energy in the form of triglycerides, but 
research in the last few decades has shown that fat cells also play a critical 
role in sensing and responding to changes in systemic energy balance. White fat 
cells secrete important hormone-like molecules such as leptin, adiponectin, and 
adipsin to influence processes such as food intake, insulin sensitivity, and 
insulin secretion. Brown fat, on the other hand, dissipates chemical energy in 
the form of heat, thereby defending against hypothermia, obesity, and diabetes. 
It is now appreciated that there are two distinct types of thermogenic fat 
cells, termed brown and beige adipocytes. In addition to these distinct 
properties of fat cells, adipocytes exist within adipose tissue, where they are 
in dynamic communication with immune cells and closely influenced by innervation 
and blood supply. This review is intended to serve as an introduction to adipose 
cell biology and to familiarize the reader with how these cell types play a role 
in metabolic disease and, perhaps, as targets for therapeutic development.