Adipose tissue, or fat, is one of the major energy storage forms in the body. One of the major energy sources is carbohydrates, which are transformed by several metabolic processes into glucose. Glucose, in turn, is the body's main energy source under normal conditions. Adipose tissue has the ability to metabolize glucose under certain conditions to provide energy for the body.
Functions of Adipose
Adipose tissue serves three main functions within the body. Heat insulation as provided by adipose tissue found just deep to the skin, allows individuals to remain warm. The amount of insulation is directly related to the thickness of the subcutaneous tissue such that a person with 2 mL of adipose beneath the skin will remain at a comfortable temperature at 15 degrees Celsius, or 59 degrees Fahrenheit compared to a person with 1 mL of adipose remaining comfortable at 16 degrees Celsius, or 60.8 degrees Fahrenheit. Adipose also serves as a mechanical cushion, surrounding and protecting internal organs. Lastly, adipose is the body's major form of energy storage.
Energy Storage and Use
Adipose serves as the body's main energy store, providing a buffer for energy imbalances should energy input not equal energy output. Energy is stored with little water, making adipose very efficient. However, glucose as derived some carbohydrates is the primary energy source for the brain, not fatty acids as are stored within adipose cells. Lipolysis is the metabolic process responsible for breaking down adipose tissue and releasing the stored energy. Triglycerides, the molecules stored within adipose cells, are broken into fatty acids and glycerol. Both of these products can be used in the metabolic processes required for glucose production.
Role of Insulin
Insulin is a major contributor when discussing metabolism. Insulin is the major facilitator that allows glucose to enter adipose and other tissues as its main role is to decrease the amount of glucose in the blood. By facilitating the entry of glucose into the adipose cell, insulin inhibits adipose tissue from undergoing lipolysis. This in turn promotes formation of triglycerides and accumulation of fat inside the adipose cell. Individuals who have excess insulin secretion, often seen in individuals with type 2 diabetes, have very low blood glucose levels that in turn starve the brain of needed energy.
Regulation
Lipolysis and, thereby, glucose metabolism, is controlled by a number of intracellular factors and enzymes. Lipolysis is regulated by an enzyme called triglyceride lipase. Fatty acids that are going to be utilized for the production of energy, ATP, undergo a process called beta-oxidation. The breakdown of adipose tissue for energy is seen more often in endurance athletes as their bodies experience energy deficits during exercise that must be made up through lipolysis.
