Fatty acids belong to a category of biological molecules called lipids (or fats), which are generally water-insoluble but highly soluble in organic solvents. Chemically, a fatty acid is a non-polar long aliphatic hydrocarbon molecule chain that has an acidic carboxylic acid group (COOH) at one end of its molecule, and a methyl group (CH3) at the other end, which is designated omega or ω. The COOH being at one end is what makes these molecules acids. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms (from four to 28). They have the general structure of CH3(CH2)nCOOH.
Fatty acids are derived from both animal and vegetable fats and oils. They are a necessary part of nutrition, and have uses outside the body (such as lubricants, cooking, soaps, detergents and cosmetics).
Fatty acids can be categorized in various ways, although they are primarily categorized through the degree of saturation or variation of chain length.
A saturated fatty acid has no double bonds. Saturated fatty acids are solid at room temperature, have high melting points and are common in animal and plant fats.
Unsaturated fatty acids have one or more double bonds, are liquid at room temperature and have low melting points. Among unsaturated fatty acids are monounsaturated fatty acids (MUFAs, fatty acids that have one double bond in the fatty acid chain) and polyunsaturated fatty acids (PUFAs, fatty acids in which the hydrocarbon chain possesses two or more carbon–carbon double bonds). PUFAs can also be conjugated.
Saturated and trans fats are generally considered to be unhealthy fats because they raise both total and low-density lipoprotein (LDL, or “bad”) cholesterol.
Fatty acid chains are found in plants and animals, and are usually in triglyceride form. These are typically unbranched (have an even number of carbons) and range from four to 24 carbon atoms, with 16- and 18-carbon lengths being the most common. They can be designated by chain length:
- Short-chain fatty acid—five or fewer carbons
- Medium-chain fatty acid—six to 12 carbons
- Long-chain fatty acid—13 to 21 carbons
- Very Long-chain fatty acid—22 or more carbons
Fatty acids are sometimes categorized by the omega groups, according to the location of their first double bond: omega-11, omega-10, omega-9, omega-8, omega-7, omega-6, omega-5 and omega-3.
Essential Fatty Acids (EFAs)
Essential fatty acids, or EFAs, are fatty acids that humans must ingest because they are biologically necessary for good health. The body cannot synthesize them, so they must be ingested through diet, hence the term “essential.” All other fatty acids can be produced by the body.
EFAs were discovered in 1923, and were designated "vitamin F." In 1929, research by George and Mildred Burr on rats showed EFAs were required to prevent disease, and are better classified as fats rather than vitamins. It was Michael Eugene Chevreul, a french chemist, who is credited with developing the termed fatty acid (acide gras).
Currently, there are two known PUFAs that are known to be essential for humans: alpha-linolenic acid (ALA, an omega-3 fatty acid) and linoleic acid (an omega-6 fatty acid). These two fatty acids cannot be synthesized by humans because we lack the desaturase enzymes required for their production.
Humans cannot synthesize double bonds in fatty acids beyond carbon 9 and 10. But they can convert these two fatty acids (alpha-linolenic acid and linoleic acid) into other long-chain or very long-chain fatty acids. However, this conversion process is not entirely fast nor efficient. Due to low conversion efficiency, ingestion of other omega-3 and omega-6 fatty acids is advised.
Conventionally, long-chain PUFAs are not considered essential. Because long-chain PUFAs are sometimes required under some developmental or disease conditions, they may be considered as “conditionally essential fatty acids,” but not essential to healthy adults.
Roles of EFAs in the body
Adequate intake of EFAs results in numerous health benefits. There are many documented benefits, which include: heart health (reduced risk of heart disease—atherosclerosis, reduction of triglycerides and blood pressure), brain health (improved cognition, depression, etc.), inflammation and joint pain (a reduction of joint pain from rheumatoid arthritis [RA]) (Curr Pharm Biotechnol. 2006 Dec;7(6):467-82). The American Heart Association recommends all adults eat fish, particularly fatty fish, at least twice weekly, which is associated with reductions in cardiovascular disease risk (Eur J Clin Nutr. 2018 May 22. DOI: 10.1038/s41430-018-0190-2).
EFA deficiency disease is rare, occurring most often in infants fed diets deficient in EFAs, according to the “Merck Manual of Diagnosis and Therapy.” Signs include scaly dermatitis, alopecia, thrombocytopenia and, in children, intellectual disability. Diagnosis is clinical. Dietary replenishment of EFAs reverses the deficiency. (Merck Manual, Professional edition).
Some researchers have suggested the relative ratio of the intakes of omega-6s and omega-3s may have important implications for the pathogenesis of many chronic diseases, such as cardiovascular disease (CVD), cancer, etc. (Clin Nutr. 2018; pii: S0261-5614(18)30082-7). Some researchers have suggested omega-6 fatty acids compete with omega-3 fatty acids for common enzymes needed for metabolism, possibly counteracting the health benefits of omega-3 fatty acids (Eur J Clin Nutr. 2016 Jul;70(7):812-8). Any optimal ratio has not yet been defined, although some recommend 1:1 and 4:1. There is data to suggest human beings evolved on a diet with a ratio of omega-6 to omega-3 EFAs 1-2:1, and now the Western diets have a ratio ranging from 10:1 to 30:1. Note no ratio has been entirely proven to be important or not.
The U.S. Department of Health and Human Services’ (HHS) National Institutes of Health (NIH) offers recommendations for omega-3 intake based on Dietary Reference Intakes (DRIs) developed by the Food and Nutrition Board of the Institute of Medicine (IOM) (now called the National Academy of Medicine). DRI is the general term for a set of reference values used for planning and assessing nutrient intakes of healthy people. These values, which vary by age and sex, include:
Adequate Intakes (AIs) for Omega-3s
The American Heart Association (AHA) also has recommendations for omega-3 intake specific to heart health. AHA advises patients without coronary heart disease (CHD) eat fatty fish at least twice weekly and consume oils and foods rich in ALA. For patients with CHD, 1 g/d of combined eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) is advised. To lower triglycerides, a dose of 2 to 4 g combined DHA and EPA is advised.
AHA further recommends people consume at least 5% to 10% of calories from omega-6 fatty acids. It's recommended the omega-6 comes from foods, not supplements.
Robin Koon is executive vice-president at Best Formulations, and has more than 35 years of pharmaceutical experience in clinical pharmacy as a retail drug chain executive overseeing operations, in managed-care and manufacturing.