Contrary to popular opinion, fat cells in adipose tissue are not simply dormant storage depots, according to Johns Hopkins Medicine Health Alerts. Fat cells are dynamic and highly active. The fat cells of adipose tissue share an extremely important role in metabolism, according to Sareen Gropper, Jack Smith and James Groff in "Advanced Nutrition and Human Metabolism." According to the National Institutes of Health, insulin stimulates fat cells to take in glucose. Triglycerides can be synthesized in the fat cells from glucose when influenced by insulin. As blood glucose levels decrease, insulin levels fall and the adipose tissue favors the breakdown of triglycerides to free fatty acids and glycerol.
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Fat cells provide triglycerides to fuel much of the body's internal work and physical activity. The layer of fat under the skin insulates the body to keep it warm. Pads of fat act as shock absorbers and support and cushion vital organs. Fat also helps the body use carbohydrate and protein. Fragments of fat metabolism combine with those of glucose in energy metabolism. Fat spares protein for other important tasks by providing energy to the body.
The body has two types of fat, white and brown adipose tissue, to perform two separate functions. The storage form, white adipose tissue, provides fat for other cells to use for energy. Brown adipose tissue releases stored energy as heat, according to Eleanor Whitney and Sharon Rolfes in "Understanding Nutrition." By radiating energy away as heat, brown adipose tissue enables the body to spend energy rather than store it. Producing heat is extremely important in newborns and in people who live in cold climates. Most adults have only small amounts of brown fat in strategic locations. The role of brown fat in body weight regulation is not yet fully understood.
When more calories of energy are consumed than are spent, most of the excess energy is stored in the fat cells of adipose tissue. Fat cells expand in size as they fill with fat droplets and may divide when they reach maximum size. When cells need energy, a hormone-sensitive lipase enzyme in the adipose cells breaks apart the triglycerides to release the glycerol and fatty acids into the blood, where they are available for other energy-hungry cells.
The fat cells continuously break down and rebuild triglycerides as needed. These processes are regulated by nutrition, hormones and metabolism factors that determine how much fatty acid circulates in the blood and how much fat the body stores. Fat provides 60 percent of the ongoing energy needs of the body at rest and a little more during prolonged activity. As research continues, an understanding of how insulin stimulates fat cells to take in glucose could lead to a fuller understanding of diabetes and related conditions, according to the National Institutes of Health.
Obesity develops as a person's fat cells increase in number, size or both. With fat loss, the size of fat cells decreases but not their number. People with extra fat cells tend to regain lost weight rapidly, according to "Understanding Nutrition."