Triglycerides are the most concentrated form of metabolic energy storage available to humans. Because triglycerides lack water, they have about twice the energy density of carbohydrates and proteins. The energy density of triglycerides is approximately 37.7 kJ/g (9 cal/g), whereas the density of carbohydrates and proteins is 16.8 kJ/g (4 cal/g). In the event of food deprivation, triglycerides are an essential source of water and energy. Some animals can rely solely on metabolic water obtained from fatty-acid oxidation for maintenance of their water balance. For instance, the hump of a camel consists largely of adipose tissue and is a source of water and energy for this desert animal.
Adipocytes perform other functions in addition to their role as fat-storage containers. They also regulate energy metabolism by secreting paracrine and endocrine substances. The newly discovered secretory functions of adipocytes have shifted views on adipose tissue, which is now considered a major  endocrine organ. Considerable evidence already exists to link increased endocrine activity of adipocytes to the metabolic and cardiovascular complications associated with obesity.
There are two types of adipose tissue: white (unilocular) and brown (multilocular).
The two types of adipose tissue, white adipose tissue and brown adipose tissue, are so named because of their color in the living state.
 White adipose tissue is the predominant type in adult humans.  Brown adipose tissue is present in humans during fetal life but diminishes during the first decade after birth.
Function of White Adipose Tissue
Functions of white adipose tissue include energy storage, insulation, cushioning of vital organs, and secretion of hormones.
White (unilocular) adipose tissue forms a layer called the panniculus adiposus [Lat. panniculus, a little garment; adipatus, fatty] or hypodermis in the connective tissue under the skin. Since the thermal conductivity of adipose tissue is only about half that of skeletal muscle, the subcutaneous layer of connective tissue provides a significant thermal insulation against cold by reducing the rate of heat loss. Concentrations of adipose tissue are found in the connective tissue under the skin of the abdomen, buttocks, axilla, and thigh. Sex differences in the thickness of this fatty layer in the skin of different parts of the body account, in part, for the differences in body contour between females and males. In both sexes, the mammary fat pad is a preferential site for accumulation of adipose tissue; the nonlactating female breast is composed primarily of this tissue. In the lactating female, mammary fat pad plays an important role in supporting breast function. It provides lipids and energy for milk production, but it is also a site for the synthesis of different growth factors that modulate responses to different steroid and proteins and hormones acting on mammary gland function.
Internally, adipose tissue is preferentially located in the greater omentum, mesentery, and retroperitoneal space and is usually abundant around the kidneys. It is also found in bone marrow and between other tissues, where it fills in spaces. In the palms of the hands and the soles of the feet, beneath the visceral pericardium (around the outside of the heart), and in the orbits around the eyeballs, adipose tissue functions as a cushion. It retains this structural function even during reduced caloric intake; when adipose tissue elsewhere becomes depleted of lipid, this structural adipose tissue remains undiminished.
White adipose tissue produces a variety of hormones, growth factors, and cytokines.