Unsaturated fat

An unsaturated fat is a fat or fatty acid in which there is at least one double bond within the fatty acid chain.

A fatty acid chain is monounsaturated if it contains one double bond, and polyunsaturated if it contains more than one double bond.

Where double bonds are formed, hydrogen atoms are eliminated. Thus, a saturated fat has no double bonds, has the maximum number of hydrogens bonded to the carbons, and therefore is "saturated" with hydrogen atoms. In cellular metabolism, unsaturated fat molecules contain somewhat less energy (i.e., fewer calories) than an equivalent amount of saturated fat. The greater the degree of unsaturation in a fatty acid (i.e., the more double bonds in the fatty acid) the more vulnerable it is to lipid peroxidation (rancidity). Antioxidants can protect unsaturated fat from lipid peroxidation.

Chemistry and nutrition

Double bonds may be in either a cis or a trans isomer, depending on the geometry of the double bond. In the cis isomer, hydrogen atoms are on the same side of the double bond, whereas, in the trans isomer, they are on opposite sides (see trans fat). Saturated fats are popular with manufacturers of processed foods because they are less vulnerable to rancidity and are, in general, more solid at room temperature than unsaturated fats. Unsaturated chains have a lower melting point, hence increasing fluidity of the cell membranes.