A fatty acid is a combination of a chain of carbon and hydrogen atoms, known as a hydrocarbon, and a particular acid group (-COOH). Three fatty-acid molecules combined with a glycerol form a triglyceride fat or oil.
While several varieties of fatty acid occur in nature, all belong in one of two categories—saturated or unsaturated. In a saturated fatty-acid molecule, all the carbon atoms in the chain are attached to two hydrogen atoms, the maximum amount. All the bonds between the carbon atoms in the chain are single electron bonds. An example of fat made of saturated fatty acids is butter.
Unsaturated fatty-acid molecules have one or more carbon atoms with only a single hydrogen atom attached. In these chains, one or more bonds between the carbon atoms are double. A molecule with one double bond is called monounsaturated, and two or more double bonds is called polyunsaturated. An example of unsaturated fat is vegetable oil.
Generally, fats consisting of saturated fatty acids are solid, and those made up of unsaturated molecules are liquid. An unsaturated fatty acid may be converted into saturated through a process called hydrogenation. While most modern diets are aimed at the reduction of fatty acids (fats), it is important to recognize that several of them, such as oleic, butyric, and palmitic acid, are important parts of the human diet. Another, linoleic acid, is absolutely essential to human life. It is an important part of a vital chemical reaction in the body, and is obtained solely through ingestion. It is found in corn, soybean, and peanut oils.
Recently, concern about the amount of trans fatty acids present in food has caused debate. Trans fatty acids are formed during the process of partial hydrogenation of unsaturated fatty acids (like vegetable oil) into margarine and vegetable shortening. Some research suggests that levels of trans fatty acids can alter the amount of cholesterol found in blood, which can be a significant risk to people suffering from high cholesterol levels and heart disease. In addition to being found in margarine, trans fatty acids are also found naturally in small quantities in beef, pork, lamb, and milk. There is conflicting evidence, however, of the dangers of trans fatty acids in daily diets. Generally, it is recommended to limit the total daily amount of fat eaten, rather than focusing solely on trans fatty acid consumption.
See also Carboxylic acids.