Glycerol is a carbohydrate that can be made in the body from glucose and obtained through the diet as a food additive. It also exists naturally in triglycerides (TGs) and phospholipids (PLs). Glycerol has applications in food manufacturing as a sweetener, thickener, solvent and preservative. Fatty acids, which are fats, can also be made in the body and obtained through the diet in TGs and PLs. Fatty acids supply more energy per gram and play a more significant role in human health than glycerol.
Triglycerides and Phospholipids
In TGs and PLs, glycerol acts is the backbone that fatty acids attach to. The glycerol backbone is like a Christmas tree with room for three ornaments. Fatty acids are like the different types of "ornaments" that can hang on the glycerol "tree." TGs contain three fatty acid ornaments, and PLs contain two fatty acids and a phosphate group. The fatty acid ornaments that decorate the glycerol tree of a TG or PL determine its biological, chemical and physiological properties. Unlike fatty acids, there is only one type of glycerol and it has less significance on the properties of the TG and PL.
Structure and Biological Function
Glycerol is a simple three-carbon molecule with a hydroxyl group on each carbon. Unlike glycerol, fatty acids are complex molecules that vary in length from four to 28 carbons long and can contain one or more double bonds. A fatty acid with one double bond is called monounsaturated; more than one double bond makes a polyunsaturated fatty acid. Experts agree the presence of double bonds in a fatty acid has implications for its biological activity and impact on human health. There is only one glycerol structure, and it has less impact on human health than fatty acids.
Some Fatty Acids are Essential
Most fatty acids can be made in the body. However, there are two essential fatty acids -- linoleic acid and alpha-linolenic acid -- that cannot be made and must be obtained from the diet. Good sources of essential fatty acids are flax, fish and walnuts.
Glycerol can be used as a source of energy. Unlike glycerol, fatty acids are important sources of fuel because they yield a large amount of energy. As part of PLs in the cell membrane, the most important biological role of glycerol is to maintain a cell's physical structure. Fatty acids also play a role in maintaining cell membrane structure but play a bigger role in the cell's function and signaling. Unlike glycerol, fatty acids alter the "fluidity" of cell membranes. The type of fatty acids that comprise a cell membrane alter the movement of ions in and out of a cell. Immunity, inflammation and cognition rely on fatty acids to act as signaling molecules between cells.
- United States Department of Agriculture: Dietary Guidelines for Americans; December 2010
- "The American Journal of Clinical Nutrition"; Receptor-mediated signaling pathways: potential targets of modulation by dietary fatty acids; Daniel Hwang, et al. October 1999
- Linus Pauling Institute: Essential Fatty Acids; Jane Higdon, et al.; December 2005