A triglyceride is a molecule formed by three fatty acid chains linked to a molecule of glycerol.
Triglycerides are carried in the blood as lipoprotein complexes (see article on "Other lipids" for more detail). Once they reach their target organ, triglycerides are split by enzymes to release the three fatty acids inside the tissues, where they are used as a source of energy or stored again as triglycerides. The visible evidence of this is the fat under the skin, but some fat can also be stored in the abdomen and organs. All tissues are able to use fats for energy, heart muscle in particular.
The amount of stored fat varies widely: in non-obese men it can make up 15% of body weight and in non-obese women, 21%. Deposition of the fat on the hips, buttocks and thighs (peripheral obesity) is believed to be less unhealthy compared with fat deposited in the abdomen (central obesity). The latter forms could be a manifestation of the metabolic syndrome with attendant increases of triglycerides, resistance to insulin, elevation of blood pressure and decrease in HDL.
There is another type of body fat known as “brown fat”, which is present more in infancy than in adulthood. This is found on the back, at the nape of the neck and around the major blood vessels. The function of brown fat is thought to be mainly concerned with insulation, heat production and for adapting to cold climates.