Fatty acids combine to make saturated or unsaturated fat. All fatty acids have “tails” or chains, which consist of an even number of carbon atoms. Some fatty acids have more carbon atoms in their tails, and these types are called long-chain fatty acids; they behave differently in your body than medium- or short-chain fatty acids. Fatty acids are important sources of fuel for your muscles and heart because they yield lots of energy when they are metabolized, although longer chains are not used as efficiently as smaller chains.
Length of Fatty Acids
The vast majority of natural fatty acids have a chain that consists of between four and 28 carbon atoms. Depending on their length, fatty acids are categorized as short-, medium-, long- or very long-chain types. Short-chain fatty acids, such as butyric acid, typically have four carbon atoms in their tails. Medium-chain fatty acids, such as caprylic acid, contain between six and 12 carbon atoms in their tails. Long-chain fatty acids, such as palmitic acid, contain between 14 and 22 carbon atoms in their tails. Finally, very long-chain fatty acids, such as cerotic acid, contain more than 22 carbon atoms in their tails.
Unsaturated Fatty Acids
Fatty acids that have double bonds in their tails are called unsaturated fats, which are commonly found in plant-based food. Some unsaturated fatty acids are categorized as essential because they are necessary for health, but your body cannot make them. Two important examples of long-chain essential fatty acids are linoleic acid, often abbreviated LA, and alpha-linolenic acid or ALA. Both LA and ALA are widely found in plant and vegetable oils, such as olive oil and sunflower oil. Linoleic acid is also known as an omega-6 fatty acid, whereas ALA is further categorized as an omega-3 fatty acid. Omega-3 fats are especially important for preventing cardiovascular diseases because they deter inflammation within blood vessels and reduce the risk of atherosclerosis and clogged arteries. Inflammation is also a common problem with arthritis and autoimmune disorders.
Saturated Fatty Acids
Fatty acids without double bonds in their tails are called saturated fats, which are most commonly found in meat and other animal-based food. Saturated fat, the most prevalent type in butter and eggs, has been linked to increased risk of cardiovascular diseases, although research over the years has not always been clear and sometimes it’s contradictory. Examples of long-chain saturated fatty acids include stearic and arachidic acids, which have tails of 18 and 20 carbons respectively.
Implications for Metabolism
Short- and medium-chain fatty acids are more easily used as energy sources compared to long chains because the shorter types are absorbed directly into the bloodstream, just like glucose, and are used by most cells to do work. In contrast, long-chain fatty acids are absorbed into the walls of the intestine and reassembled into triglycerides, which are then coated with cholesterol and protein. These compounds are transported to various tissues around the body and stored. They are only metabolized for energy when carbohydrates and shorter chain fats run out.
- Human Biochemistry; Charles Dreiling
- Human Physiology: An Integrated Approach; Dee Silverthorn and William Ober
Sirah Dubois is currently a PhD student in food science after having completed her master's degree in nutrition at the University of Alberta. She has worked in private practice as a dietitian in Edmonton, Canada and her nutrition-related articles have appeared in The Edmonton Journal newspaper.