Fats are organic compounds that are made up of carbon, hydrogen, and oxygen; they are the most concentrated source of energy in foods. Fats belong to a group of substances called lipids. Fats come in liquid or solid form. All fats are combinations of saturated and unsaturated fatty acids. Fats can be called very saturated or very unsaturated depending on their proportions.

Fat is one of the three nutrients (along with protein and carbohydrates) that supply calories to the body. Fat provides 9 Calories per gram, more than twice the number provided by carbohydrates or protein.

Fat is essential for the proper functioning of the body. Fats provide the "essential" fatty acids, which are not made by the body and must be obtained from food. Linoleic acid is the most important essential fatty acid, especially for the growth and development of infants. Fatty acids provide the raw materials that help in the control of blood pressure, blood clotting, inflammation, and other body functions.

Fat serves as the storage substance for the body's extra calories. It fills the fat cells (adipose tissue) that help insulate the body. Fats are also an important energy source. When the body has used up the calories from carbohydrate, which occurs after the first 20 minutes of exercise, it begins to depend on the calories from fat.

Healthy skin and hair are maintained by fat. Fat helps in the absorption, and transport through the bloodstream of the fat-soluble vitamins A, D, E, and K.