lipids
Lipids play several important roles in the body. Triglycerides are stored in fat cells until the body needs to break them down for chemical energy. These stored triglycerides also help insulate the body against extreme temperatures and cushion organs against physical jostling. Phospholipids and cholesterol are important constituents of the cell membrane. These compounds provide structural integrity to the cell wall, since they are not water-soluble. Other steroids are used as chemical messengers in the body, and the fat-soluble vitamins serve a variety of other functions.