Perhaps no term in food science has gained a worse reputation than the word fat. Just the mere mention of the word can bring shivers to the spines of nutritionists and consumers everywhere. However, it is important to remember that fats are an essential part of a proper diet and an important constituent in many types of food products. Lipids are the primary source of the fat-soluble vitamins A, D, E and K and are a concentrated source of energy providing over twice the energy of carbohydrates or protein. In addition, fats and oils add function, taste and palatability to many types of foods. However, the consumption of specific lipids and their potential impact on health remains an extremely important dietary issue.
Although the exact origins of the terms fats and lipids in connection with a chemical component of foods is unclear, both words can be traced to ancient times. The word lipid is derived from the Greek "lipos," meaning fat. The Old English word "faett," appeared in the classic ninth century tale of Beowulf and was used to describe vessels or vats of large size. Through the decades, the term found its way into the popular lexicon and the meaning expanded. A popular proverb of the 1600s declared that "Every Fatt must stand on his own bottom." In the 1860s, the term fatt was used in some references as a measure equal to approximately nine gallons. Over the years, the terms fat and lipid have been used interchangeably to describe a group of chemical compounds including triacylglycerol (i.e., triglycerides), phospholipids, and sterols. Fatty acids are so named due to their role as the key components of lipids and their structure which contains an organic acid group (i.e., COOH).
Fast Facts on Fat
Lipids are present in, and derived from, both plant and animal sources. The primary constituents of these fats are triglycerides which account for about 90% of the fats in food and over 90% of the fat in the body. Other minor components include sterols, and mono- and diglycerides. Plant sterols include campesterol, stigmasterol and ß-sitosterol. Cholesterol is found almost exclusively in animal fats.
Although these substances are often unrelated physiologically and chemically, their classification is based upon their solubility in nonpolar solvents (e.g., chloroform, benzene, ether, alcohol). Structurally, triglycerides consist of fatty acids which are a linear chain of atoms, with one end composed of a carboxyl group and the other end being a methyl group. The chemical structure of lipids is extremely important in their classification and properties. The number of carbon and hydrogen atoms as well as number and position of double bonds determine the physical characteristics and metabolic properties of the fat.
Fatty acids are the building blocks of lipids and comprise 85%-95% of the fats in foods. It is these compounds that are of interest when reporting the lipid content of foods for nutrition labeling. Fatty acids are given a numeric classification. The first number is the length of the carbon chain and the second number represents the number of double bonds found in the chain. For example, linoleic acid is comprised of 18 atoms and two double bonds resulting in a chemical classification of 18:2. Short chain fatty acids are generally defined as having a carbon chain length of up to four. Medium chain have 6-12 and long chain have a chain length greater than 12. It is the chemical structure of these fatty acids that is a key to the physiological effects of the triglyceride.