An adipocyte is a fat cell. Adipocytes are found in deposits of fatty tissue all over the body. These specialized cells also appear to be capable of secreting hormones and other chemicals which may play a role in appetite regulation and other aspects of the metabolism. The number of the adipocytes in the body remains constant, with around a 10th of the adipocyte cells being renewed each year.
There are two kinds of adipocytes: white adipocytes and brown adipocytes. White fat cells are involved in the storage of fat, with much of the cell being filled with a large droplet of oil, and the nucleus being crushed against the side of the cell wall. Brown fat cells are used to generate heat for the body, and they have structures which include a number of small oil drops mixed with the regular cell cytoplasm, with a brown appearance due to the iron in the mitochondria of the cell.
Levels of white and brown fatty tissue fluctuate as people mature. In childhood, there is more brown adipose tissue, especially in infants, and this fat is sometimes referred to as “baby fat.” As people grow older, the brown cells convert to white cells. The conversion usually is associated with other physical changes which occur as people mature, including rearrangement of fat deposits on the body.
One might be led to wonder why weight fluctuates if the number of adipocytes remains constant. These cells are capable of expanding to hold more fat, and also of shrinking as their fat reserves are depleted. White adipocytes will swell to store excess fat when they can get it, building up a reserve, and when people eat restrictive diets, the cells will release some of their fat and take on a shriveled appearance. Thus, people can change the amount of fat stored in their bodies without actually changing the numbers of adipocyte cells.
While the adipocyte has come to be viewed as the enemy by legions of dieters, these cells actually play an important role in the body. Fat provides insulation and shock absorption which protects the core of the body from damage, and it also serves as an energy reserve which can be used when the body is not getting enough energy. The much-maligned adipocyte is one of the many types of cells which has evolved in nature for a specific purpose, which in this case happens to be the storage of fat.