In the body fat serves as an efficient source of energy and stored in adipose tissue. It provides building blocks for different high molecular weight substances, e.g. acetic acid for the synthesis of cholesterol and certain hormones. Fats contain essential fatty acids viz, linoleic, linolenic, and arachidonic acids which are essential for maintaining tissues in normal health.  They serve as a thermal insulator in the subcutaneous tissues and around vital organs. Nonpolar lipids act as electrical insulators allowing rapid propagation of depolarization waves along myelinated nerves. The fat content of nerve tissue is very high. Combinations of fat and protein (lipoproteins) are important cellular constituents, occurring in the cell membrane mitochondria and cytoplasm. They serve also as the means of transporting lipids in the blood.