Fatty Acid
Fatty acids are carboxylic acids characterized by a carboxyl group and a long aliphatic chain made up of carbon, hydrogen, and oxygen. They are categorized into saturated and unsaturated fatty acids based on the presence of double or triple bonds between carbon atoms, and their chains can vary in length from short-chain (fewer than six carbon atoms) to very long-chain (22 or more carbon atoms). Fatty acids serve as a vital source of energy, particularly for heart and skeletal muscle cells, as they are metabolized to produce adenosine triphosphate (ATP). Certain fatty acids, designated as essential, cannot be synthesized by the body and must be obtained through diet. Notable examples include alpha-linolenic acid and linoleic acid, which play crucial roles in cellular function and health. Sources of these essential fatty acids include various plant oils, nuts, and animal fats. Omega-3 and omega-6 fatty acids, recognized for their health benefits, are increasingly important in modern diets but are often lacking due to limited consumption of marine foods. Research suggests that these fatty acids may contribute to improving cardiovascular health, cognitive function, and other aspects of well-being.
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Subject Terms
Fatty Acid
A fatty acid is a carboxylic acid, a group of compounds containing a carboxyl group and expressed as R-C(O)OH, where C(O)OH is the structure of carbon, oxygen, and hydrogen atoms that comprises the carboxyl group and R is the remainder of the molecule. Specifically, fatty acids are saturated or unsaturated carboxylic acids with a chain of non-aromatic compounds (also known as aliphatic compounds, one of two classes of compounds made up of carbon and hydrogen). Fatty acids are thus composed of just three elements in various configurations: carbon, oxygen, and hydrogen. Fatty acids are used as fuel by various cells in an organism, and are especially useful in this role for heart and skeletal muscle cells. When metabolized by the cell, they provide adenosine triphosphate (ATP), the coenzyme used to transfer energy intracellularly.
Background
Fatty acids both occur naturally and are produced on an industrial scale, usually by removing glycerol from triglycerides. Fatty acids found in nature almost always have an even number of carbon atoms in their aliphatic chain, somewhere between 4 and 28. They are differentiated according to whether they are saturated or unsaturated—as with all hydrocarbons, fatty acids are called "unsaturated" if they have double or triple covalent bonds between their carbon atoms—and by the length of their chains. From shortest to longest, they 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 body handles fatty acids differently according to the length of their aliphatic chain. Long-chain fatty acids, for instance, require the presence of bile salts (formed in the liver from bile acids and taurine or glycine) for humans to digest them, and must go through several transformations to be used. First the fatty acids are absorbed into protrusions in the intestinal wall called villi, which combine glycerol with long-chain fatty acids to form triglycerides. Triglycerides are then combined with proteins and cholesterol to form chylomicrons, one of the major groups of lipoproteins that transport particles of fat and cholesterol through the bloodstream, into which they are released by the lymphatic system. Medium- and short-chain fatty acids are more easily and quickly digested, and so are sometimes used to treat patients with malnutrition, since they are passively diffused from the GI tract instead of requiring energy for the body to use them.
Overview
Certain fatty acids are both necessary for human health and are not synthesized in the body. This is known to be true for alpha-linolenic acid and linoleic acid (originally classified as Vitamin F when they were discovered in 1923), and is true for some other fatty acids for patients suffering from certain diseases, and may prove to be true for still others. Essential fatty acids are used by the body to act on DNA in critical ways, as well as to form substances like lipoxins, eicosanoids, endocannabinoids, isofurans, neurofurans, isoprostanes, hepoxilins, and lipid rafts. These substances are important at both the micro level, where they are used for important cellular functions like signaling and inflammation, and at the macro level, where they impact mood and behavior. These essential fatty acids are found in numerous plant oil sources (alpha-linolenic acid is found mainly in seeds, while linoleic acid is found mainly in nuts), as well as in animal and dairy fats, cocoa butter, and egg yolk. Understanding the use and essentiality of fatty acids was an important discovery in the history of modern medicine; better infant formulas could be devised, for instance, once it was discovered in the 1950s that infants raised on skim milk were more likely to experience developmental problems such as limited growth and unhealthy skin. (Fatty acids are present in the fat or cream of milk, and so skim milk possesses the smallest concentration).
A phrase familiar from food and supplement labeling is "omega-3 fatty acid," which refers to the location of the first double bond on the fatty acid’s tail, or omega. Other omega-numbered fatty acids are omega-6, omega-7, and omega-9. Alpha-linolenic acid is an omega-3, while linoleic acid is an omega-6. Omega-3 fatty acids used by the human body also include eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), both found in marine food sources like phytoplankton and algae, and (more commonly, in the human diet) in the fats of fish who feed on them. Omega-3 fatty acids appear to have numerous human health benefits, many of which are still being discovered. Studies have found that DHA, for instance, slows the progression of Alzheimer disease and mental decline in the elderly, inhibits the growth of colon cancer cells, improves cardiovascular health, reduces the risk of developing Parkinson's disease, and assists stroke victims in recovery. It has even been posited as a contributing factor in the evolution of the human brain and its large size relative to other primates. EPA has been studied for treatments of depression and schizophrenia, and in regimens that improve the efficacy of chemotherapy for cancer patients.
Most modern humans do not eat a diet that is rich in marine food sources like oily saltwater fish, which is why supplements containing fish oil have become popular. The efficacy of such supplements is questionable, however; some studies have found that fish oil pills are often heavily oxidized, which is believed to impact their efficacy in the body. DHA-fortified food items have become more common in the twenty-first century, and NASA sponsored the development of an algae-based omega-3 supplement in the 1980s, which is suitable for use by vegans.
Bibliography
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Lawrence, Glen. The Fats of Life: Essential Fatty Acids in Health and Disease. Newark: Rutgers UP, 2010. Print.
Mostofsky, David I., Shlomo Yehuda, and Norman Salem, Jr., eds. Fatty Acids: Physiological and Behavioral Functions. New York: Humana, 2001. Print.
Ridgeway, Neale, and Roger McLeod, eds. Biochemistry of Lipids, Lipoproteins, and Membranes. New York: Elsevier, 2015. Print.
Schroeder, Jens-M., ed. Fatty Acids and Inflammatory Skin Diseases. New York: Birkhauser, 2013. Print.
Shahidi, Fereidoon, and John W. Finley, eds. Omega-3 Fatty Acids: Chemistry, Nutrition, and Health Effects. Washington DC: American Chemical Soc., 2001. Print.
Valentine, Raymond C., and David L. Valentine. Human Longevity: Omega-3 Fatty Acids, Bioenergetics, Molecular Biology, and Evolution. Boca Raton: CRC, 2014. Print.
Watson, Ronald Ross, and Fabien De Meester, eds. Omega-3 Fatty Acids in Brain and Neurological Health. Waltham: Academic, 2014. Print.