Back More
Salem Press

Table of Contents

Magill’s Medical Guide, 9th Edition

Fatty acid

by Charles Vigue, , PhD, Bill Kte’pi, , MA

Category: Biology

Anatomy or system affected: Cells

Specialties and related fields: Biochemistry, metabolism

Definition: carboxylic acids that contain long aliphatic hydrocarbon chains that serve as an energy source, structural compounds primarily in membranes and as precursors for other important biologically active compounds.

Key terms:

α-linolenic acid (ALA): an essential fatty acid from which EPA and DHA are synthesized

docospantaenoic acid(DHA): an omega-3 fatty acid with 22 carbons and six carbon-carbon double bonds

eicosapentaenoic acid(EPA): an omega-3 fatty acid with 20 carbons and five carbon-carbon double bonds

essential fatty acid: a fatty acid that cannot be synthesized by humans

γ-linolenic acid (GLA): an essential fatty acid from which other fatty acids are synthesized

leukotriene: fatty acid-derived compounds that mediate inflammation and cause constriction of the bronchioles

nonsteroidal anti-inflammatory drugs(NSAIDs): compounds that inhibit the synthesis of prostaglandins and thromboxanes

omega-3(w-3 or n-3) fatty acid: an unsaturated fatty acidwith a carbon-carbon double bond, three carbons from the methyl end of the hydrocarbonchain

prostacyclin: a fatty acid-derived compound that inhibit platelet aggregation and blood clotting and act as vasodilators

prostaglandin: a fatty acid-derived compound that inhibit platelet aggregation and blood clotting, act as vasodilators, mediate inflammation and increase the perception of pain

saturated fatty acid: a fatty acid with no carbon-carbon double bonds

trans fatty acid: a fatty acid with at least one carbon-carbon double bond where the hydrogens attached to the carbons that participate in the double bond are on opposite sides of the double bond

thromboxane: a fatty acid-derived compound that are vasodilators and promote platelet aggregation and blood clotting

unsaturated fatty acid: a fatty acid with at least one carbon-carbon double bond

STRUCTURE AND FUNCTIONS

A fatty acid is a carboxylic acid with a long aliphatic hydrocarbon chain. Fatty acids serve as cellular energy sources, cellular structural components especially within membranes, and precursors for other important biological compounds such as the eicosanoids prostaglandins, thromboxanes, prostacyclins, and leukotrienes.

Naturally occurring fatty acids are usually found esterified to glycerol to form glycerides. Mono-, di and triglycerides have one, two and three fatty acids esterified to glycerol, respectively. Fatty acids found in nature usually have an even number of carbon atoms numbering as high as 24 or more although 16 and 18 are the most common. From shortest to longest, fatty acids are often grouped as short-chain fatty acids (with fewer than six carbon atoms, such as butyric acid, the fatty acid that provides the unpleasant smell of both human vomit and rancid dairy products), medium-chain fatty acids (with 6-12 carbons, often found as part of medium-chain triglycerides), long-chain fatty acids (13-21 carbons), or very long-chain fatty acids (22 or more carbons). The carbon atoms are numbered from the carboxyl group (carbon 1) to the methyl (-CH3) end. Fatty acids are referred to as saturated if they have no carbon-carbon double bonds, and unsaturated they have no carbon-carbon double bonds. Palmitic and stearic acids are examples of naturally-occurring 16-carbon and 18-carbon saturated fatty acids, respectively. Mono- and di-unsaturated fatty acids have one and two carbon-carbon double bonds, respectively. Palmitoleic and oleic acids are examples of naturally-occurring 16-carbon and 18-carbon monounsat- urated fatty acids, respectively. Polyunsaturated fatty acids have three or more carbon-carbon double bonds. omega-3 (w-3 or γ3) fatty acids such as linolenic acid have a double bond three carbons from the non-carboxyl end of the amino acid. (Omega is the last letter of the Greek alphabet.) Double bonds can be either in the cis position where the hydrogen atoms on either side of the double bond are on the same side of the hydrocarbon chain, or in the trans position where the hydrogen atoms are on opposite sides of the chain. Trans fatty acids have at least one double bond. A cis double bond bends the hydrocarbon chain about 45 degrees. At room temperature, medium and longer chain saturated fatty acids such as those found in palm and coconut oil, which can contain up to 48% saturated fatty acids, are solid at room temperature, whereas unsaturated fatty acids of the same length such as those found in peanut, corn and canola oils which can contain nearly 90% unsaturated fatty acids are liquid.

Humans can catabolize all fatty acids normally consumed in the diet. The process, called β-oxidation, occurs in the mitochondria of the liver and completely metabolized the hydrocarbon chain to energy (ATP), carbon dioxide and water. The carbon atoms derived from fatty acids cannot be used to synthesize glucose or other sugars. Most fatty acids required by humans can easily be synthesized from any two-carbon source which are usually derived from glucose metabolism. Fatty acid synthesis occurs in the cytoplasm by a multi-subunit enzyme complex called fatty acid synthase whose main product is the 16-carbon saturated palmitic acid. Longer chains can be synthesized by adding two-carbon units to the carboxyl end of the fatty acid. Animals can place double bonds in the hydrocarbon chain, but not beyond carbon 9. Thus, a-linoleic acid, with double bonds at carbons 9 and 12, a-linolenic acid (ALA), with double bonds at carbons 9, 12 and 15, and g-linolenic acid (GLA) with double bonds at carbons 6, 9 and 12 are essential fatty acids. These fatty acids must be acquired by consuming plants, since plants can synthesize fatty acids that contain double bonds beyond carbon 9. Many longer-chain fatty acids required by humans can be synthesized from linolenic and linoleic acids via a combination of elongation and desaturation. Eicosapentaenoic acid (EPA), an omega-3 fatty acid with 20 carbons and five double bonds, and docosahexaenoic acid (DHA), a 22-carbon fatty acid with six double bonds, can be synthesized from linolenic acid and arachidonic acid (ARA), a 20-carbon non-essential fatty acid with 4 double bonds, but not fast enough and in quantities sufficient enough for fetuses and infants where DHA is utilized for retinal and neuronal development. Both EPA and DHA are found in marine food sources like phytoplankton, algae and oily fish that have consumed phytoplankton and algae. Although human breast milk contains ARA, EPA and DHA the concentrations vary and largely depends on the mother’s diet. ARA and DHA were first introduced into infant formula in Europe. They were introduced into infant formula in the United States in 2002.

Important biological compounds synthesized from fatty acid precursors are the eicosanoids which include prostaglandins, thromboxanes, and leukotrienes. Prostaglandins inhibit platelet aggregation and blood clotting, act as vasodilators, mediate inflammation and increase the perception of pain. Thromboxanes are vasodilators and promote platelet aggregation and blood clotting. Aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit the synthesis of prostaglandins and thromboxanes and are often prescribed as a preventative of heart attacks, to reduce inflammation and pain. Thromboxane receptor agonists can also inhibit the function of thromboxanes. Leukotrienes mediate inflammation and cause constriction of the bronchioles. Inhibitors of leukotriene receptors, such as montelukast (Singulair) are often prescribed to treat asthma.

Fatty acids are usually consumed as triglycerides which are emulsified by bile and digested in the small intestine by lipases that cleave the triglycerides into fatty acids, glycerides and glycerol. The fatty acids, glycerides and glycerol are absorbed into the intestinal mucosae. Short- and medium-chain fatty acids are transported via the blood bound to a blood protein called albumin. Long-chain fatty acids are resynthesized into triglycerides in the intestinal mucosae and transported to the liver through the lymphatic system via lipoprotein particles called chylomicrons. Fatty acids can immediately be used as an energy source or stored as triglycerides in various tissues. Several genetic diseases of fatty acid metabolism are known.

DISORDERS AND DISEASES

The most common disease of fatty acids is essential fatty acid (EFA) deficiency which can lead to a variety of symptoms including inflammatory conditions such as arthritis, hypertension, immune disorders, mental disorders, eczema, atherosclerosis and diabetes. Many of the symptoms of EFA deficiency can be improved with administration and/or consumption of essential fatty acids.

Several studies have concluded that a diet high in S-3 fatty acids such as EPA and DHA derived from oily fish have a positive effect on cardiovascular health by preventing stroke by reducing blood triglycerides, blood pressure and blood clotting. EPA and DHA may compete with precursors to thromboxane synthesis and reduce the level of thromboxanes involved with blood clotting that may lead to stroke. However, large systematic literature reviews have failed to establish that dietary supplementation with fish oil significantly decreases the risk for death, cancer, stroke, or heart disease. More work remains to be done. EPA, DHA and GLA can be converted to eicosanoid compounds that inhibit the inflammatory response and are modestly effective in the treatment for rheumatoid arthritis.

For Further Information:

1 

Abad-Jorge, Ana. The Role of DHA and ARA in Infant Nutrition and Neurodevelopmental Outcomes. Today’s Dietitian 10, No. 10 P. 66 (October 2008).

2 

Ahmad, Moghis U., ed. Fatty Acids: Chemistry, Synthesis, and Applications. New York: Academic Press and ACCS Press, 2017.

3 

Bogash, James. Healthy Fats: Sorting Through the Hype of FishOilsand the Omega-3Fatty Acids. (Self Published), 2013.

4 

Lawrence, Glen D. The Fatsof Life: Essential Fatty Acids in Health and Disease. Piscataway, NY: Rutgers University Press, 2010.

5 

McColl. Janice. “An Introduction to Essential Fatty Acids in Health and Nutrition.” Bioriginal Food & Science Corporation, 2017. www.bioriginal.com/page-articles/an-introduction-to- essential-fatty-acids-in-health-and-nutrition/

6 

Ridgeway, Neale, and Roger McLeod, eds. Biochemistry of Lipids, Lipoproteins, and Membranes. New York: Elsevier, 2015.

7 

Today’s Dietitian: www.todaysdietitian.com/newarchives/092208p66.shtml

8 

Valentine, Raymond C. and David L. Valentine. Human Longevity: Omega-3Fatty Acids, Bioenergetics, Molecular Biology, and Evolution. Boca Raton, FL: CRC Press, 2015.

9 

Watson, Ronald Ross and Fabien De Meester, eds. Handbook of Lipidsin Human Function: Fatty Acids. New York: Academic Press and ACCS Press, 2015.

10 

Watson, Ronald Ross and Fabien De Meester, eds. Omega-3Fatty Acids in Brain and NeurologicalHealth. Waltham: Academic, 2014.

Citation Types

Type
Format
MLA 9th
Vigue, Charles, and Bill Kte’pi. "Fatty Acid." Magill’s Medical Guide, 9th Edition, edited by Anubhav Agarwal,, Salem Press, 2022. Salem Online, online.salempress.com/articleDetails.do?articleName=MMG2022_0500.
APA 7th
Vigue, C., & Kte’pi, B. (2022). Fatty acid. In A. Agarwal, (Ed.), Magill’s Medical Guide, 9th Edition. Salem Press. online.salempress.com.
CMOS 17th
Vigue, Charles and Kte’pi, Bill. "Fatty Acid." Edited by Anubhav Agarwal,. Magill’s Medical Guide, 9th Edition. Hackensack: Salem Press, 2022. Accessed September 16, 2025. online.salempress.com.