The human body uses lipids for a variety of applications, including as a fuel source, to construct membranes and to protect and insulate the body. While ingesting too many lipids can cause health problems, the ingestion of some is necessary. Lipids occur naturally as oils, fats and waxes.
Lipids that are solid at room temperature are called fats. The human body uses fats primarily as an emergency food source. This is because fats are more calorically dense than any other type of macromolecule, making them the most efficient substance for storing energy. When an animal eats more food than it needs, it stores the excess energy in the chemical bonds of lipids. Later, when the animal needs to access these reserves, it breaks the chemical bonds, releasing energy.
Additionally, the human body relies on fat to help insulate the body from cold temperatures. Other animals use fats in the same way, such as seals, polar bears and other creatures living in cold climates. Lipids repel water, which makes them very useful molecules for a body that is 60 percent water. By using lipids to form membranes, the body can channel and contain water where it needs. Lipids also work to protect some delicate structures of the body. For example, the fat found around a human’s internal organs helps to protect these important structures from damage.