Fats are a group of chemical compounds that contain fatty acids. Energy is stored in the body mostly in the form of fat. Fat is also needed in the diet to supply essential fatty acids, substances essential for growth but not produced by the body itself. The terms fat and fatty acids are frequently used interchangeably.
All fatty acids are chains of carbon atoms with hydrogen atoms attached to the carbon atoms.
A saturated fatty acid has the maximum possible number of hydrogen atoms attached to every carbon atom. In some fatty acids, a pair of hydrogen atoms in the middle of a chain is missing, creating a gap that leaves two carbon atoms connected by a double bond rather than a single bond. The fat in foods contains a mixture of saturated, monounsaturated and polyunsaturated fatty acids. In foods of animal origin, a large proportion of fatty acids are saturated. In contrast, in foods of plant origin and some seafoods, a large proportion of the fatty acids are monounsaturated and polyunsaturated.