Adipose cells are the main structures in the body that store fat. Also called adipocytes, they are composed primarily of fat droplets and comprise the majority of cells in adipose tissue. This connective tissue is located in deposits called depots all over the body; it resides under the skin, around the organs, and in the bone marrow. There are two types of adipose cells, white and brown, named according to their physical appearance.
White adipose cells form the most common fat deposits in adult human beings. These types of cells contain one large droplet of fat. Their main purpose is to store fat that the body can later break down and release as fatty acids for use as energy. They also help to insulate the body and regulate its temperature, as well as provide a cushion between organs and between the skin and muscles.
The other type of adipose cells, which form brown adipose tissue, are most common in newborns. Unlike white adipose cells, the brown variety are made up of a number of small fat droplets. This type of fat is specifically designed to help infants stay warm, as they are much more susceptible to cold than adults. Some brown adipose does remain in adults, however it is much less important, as a fully grown human being is far more capable of regulating his or her body temperature without it.
Excess fats that are ingested in the diet are stored in the white adipose cells. In addition to the amount of fat in one's diet, other factors can also play a role in how much fat is contained within the cells, including genetics, hormones, and level of physical activity. The purpose of this fat storage is to keep a reserve of excess fuel for times when food is scarce or extra energy is needed. In many cases where intake of fats is far beyond what the body needs, people may store too much and become overweight or obese.
In people who are obese, adipose cells are different than in those who are not. The amount of adipose tissue in the body increases beyond normal, typically in most or all of the adipose depots. Metabolism within the cells also changes, causing them to store more fat than usual. The adipose tissue displays overall, ongoing inflammation, which can contribute to insulin resistance in the body.