What is a fatty acid?
Fatty acid
Malonyl-CoA is then involved in a repeating series of reactions that lengthens the growing fatty acid chain by two carbons at a time. Almost all natural fatty acids, therefore, have even numbers of carbon atoms. When synthesis is complete the free fatty acids are nearly always combined with glycerol (three fatty acids to one glycerol molecule) to form triglycerides, the main storage form of fatty acids, and thus of energy in animals. However, fatty acids are also important components of the phospholipids that form the phospholipid bilayers out of which all the membranes of the cell are constructed (the cell wall, and the membranes that enclose all the organelles within the cells, such as the nucleus, the mitochondria, endoplasmic reticulum, and the Golgi apparatus).
Pentacosylic acid
Pentacosylic acid, or pentacosanoic acid, or hyenic acid, is a 25-carbon long-chain saturated fatty acid with the chemical formula CH(CH)COOH.
Fatty acid synthesis
The pyruvate produced by glycolysis is an important intermediary in the conversion of carbohydrates into fatty acids and cholesterol. This occurs via the conversion of pyruvate into acetyl-CoA in the mitochondrion. However, this acetyl CoA needs to be transported into cytosol where the synthesis of fatty acids and cholesterol occurs. This cannot occur directly. To obtain cytosolic acetyl-CoA, citrate (produced by the condensation of acetyl CoA with oxaloacetate) is removed from the citric acid cycle and carried across the inner mitochondrial membrane into the cytosol. There it is cleaved by ATP citrate lyase into acetyl-CoA and oxaloacetate. The oxaloacetate can be used for gluconeogenesis (in the liver), or it can be returned into mitochondrion as malate. The cytosolic acetyl-CoA is carboxylated by acetyl CoA carboxylase into malonyl CoA, the first committed step in the synthesis of fatty acids.
Butyric acid
Butyric acid is a fatty acid occurring in the form of esters in animal fats. The triglyceride of butyric acid makes up 3–4% of butter. When butter goes rancid, butyric acid is liberated from the glyceride by hydrolysis, leading to the unpleasant odor. It is one of the fatty acid subgroup called short-chain fatty acids. Butyric acid is a medium-strong acid that reacts with bases and affects many metals.
Butyric acid
Butyric acid (from , meaning "butter"), also known under the systematic name butanoic acid, is a carboxylic acid with the structural formula CHCHCH-COOH. Salts and esters of butyric acid are known as butyrates or butanoates. Butyric acid is found in animal fat and plant oils, bovine milk, breast milk, butter, parmesan cheese, and as a product of anaerobic fermentation (including in the colon and as body odor). Butyric acid has a taste somewhat like butter and an unpleasant odor. Mammals with good scent detection abilities, such as dogs, can detect it at 10 parts per billion, whereas humans can only detect it in concentrations above 10 parts per million. In food manufacturing, it is used as a flavoring agent.
Stearic acid
Stearic acid ( , ) is a saturated fatty acid with an 18-carbon chain and has the IUPAC name octadecanoic acid. It is a waxy solid and its chemical formula is CHCOH. Its name comes from the Greek word στέαρ ""stéar"", which means tallow. The salts and esters of stearic acid are called stearates. As its ester, stearic acid is one of the most common saturated fatty acids found in nature following palmitic acid. The triglyceride derived from three molecules of stearic acid is called stearin.
Omega-3 fatty acid
The 'essential' fatty acids were given their name when researchers found that they are essential to normal growth in young children and animals. The omega−3 fatty acid DHA, also known as docosahexaenoic acid, is found in high abundance in the human brain. It is produced by a desaturation process, but humans lack the desaturase enzyme, which acts to insert double bonds at the ω and ω position. Therefore, the ω and ω polyunsaturated fatty acids cannot be synthesized, are appropriately called essential fatty acids, and must be obtained from the diet.
Ketogenic diet
On the ketogenic diet, carbohydrates are restricted and so cannot provide for all the metabolic needs of the body. Instead, fatty acids are used as the major source of fuel. These are used through fatty-acid oxidation in the cell's mitochondria (the energy-producing parts of the cell). Humans can convert some amino acids into glucose by a process called gluconeogenesis, but cannot do this by using fatty acids. Since amino acids are needed to make proteins, which are essential for growth and repair of body tissues, these cannot be used only to produce glucose. This could pose a problem for the brain, since it is normally fuelled solely by glucose, and most fatty acids do not cross the blood–brain barrier. However, the liver can use long-chain fatty acids to synthesise the three ketone bodies β-hydroxybutyrate, acetoacetate and acetone. These ketone bodies enter the brain and "partially" substitute for blood glucose as a source of energy.
Fatty acid
Fatty acids differ by length, often categorized as short to very long.
Fat
Fatty acid chains may also differ by length, often categorized as short to very long.
Any of these aliphatic fatty acid chains may be glycerated and the resultant fats may have tails of different lengths from very short triformin to very long, e.g., cerotic acid, or "hexacosanoic acid", a 26-carbon long-chain saturated fatty acid. Long chain fats are exemplified by tallow (lard) whose chains are 17 carbons long. Most fats found in food, whether vegetable or animal, are made up of medium to long-chain fatty acids, usually of equal or nearly equal length. Many cell types can use either glucose or fatty acids for this energy. In particular, heart and skeletal muscle prefer fatty acids. Despite long-standing assertions to the contrary, fatty acids can also be used as a source of fuel for brain cells.
Fatty acid metabolism
In animals, as well as some fungi such as yeast, these same reactions occur on fatty acid synthase I (FASI), a large dimeric protein that has all of the enzymatic activities required to create a fatty acid. FASI is less efficient than FASII; however, it allows for the formation of more molecules, including "medium-chain" fatty acids via early chain termination. Enzymes, acyltransferases and transacylases, incorporate fatty acids in phospholipids, triacylglycerols, etc. by transferring fatty acids between an acyl acceptor and donor. They also have the job of synthesizing bioactive lipids as well as their precursor molecules.
Triglyceride
A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) is an ester derived from glycerol and three fatty acids (from "tri-" and "glyceride"). Triglycerides are the main constituents of body fat in humans and other animals, as well as vegetable fat. They are also present in the blood to enable the bidirectional transference of adipose fat and blood glucose from the liver, and are a major component of human skin oils.
Monounsaturated fat
Common monounsaturated fatty acids are palmitoleic acid (16:1 n−7), cis-vaccenic acid (18:1 n−7) and oleic acid (18:1 n−9). Palmitoleic acid has 16 carbon atoms with the first double bond occurring 7 carbon atoms away from the methyl group (and 9 carbons from the carboxyl end). It can be lengthened to the 18-carbon cis-vaccenic acid. Oleic acid has 18 carbon atoms with the first double bond occurring 9 carbon atoms away from the carboxylic acid group. The illustrations below show a molecule of oleic acid in Lewis formula and as a space-filling model.
Fatty amine
Fatty amines are commonly prepared from fatty acids; which are themselves obtained from natural sources, typically seed-oils. The overall reaction is sometimes referred to as the Nitrile Process and begins with a reaction between the fatty acid and ammonia at high temperature (>250 °C) and in the presence of a metal oxide catalyst (e.g., alumina or zinc oxide) to give the fatty nitrile.
Fatty acid metabolism
Fatty acids are released, between meals, from the fat depots in adipose tissue, where they are stored as triglycerides, as follows:
In the liver oxaloacetate can be wholly or partially diverted into the gluconeogenic pathway during fasting, starvation, a low carbohydrate diet, prolonged strenuous exercise, and in uncontrolled type 1 diabetes mellitus. Under these circumstances oxaloacetate is hydrogenated to malate which is then removed from the mitochondrion to be converted into glucose in the cytoplasm of the liver cells, from where it is released into the blood. In the liver, therefore, oxaloacetate is unavailable for condensation with acetyl-CoA when significant gluconeogenesis has been stimulated by low (or absent) insulin and high glucagon concentrations in the blood. Under these circumstances acetyl-CoA is diverted to the formation of acetoacetate and beta-hydroxybutyrate. Acetoacetate, beta-hydroxybutyrate, and their spontaneous breakdown product, acetone, are frequently, but confusingly, known as ketone bodies (as they are not "bodies" at all, but water-soluble chemical substances). The ketones are released by the liver into the blood. All cells with mitochondria can take ketones up from the blood and reconvert them into acetyl-CoA, which can then be used as fuel in their citric acid cycles, as no other tissue can divert its oxaloacetate into the gluconeogenic pathway in the way that this can occur in the liver. Unlike free fatty acids, ketones can cross the blood-brain barrier and are therefore available as fuel for the cells of the central nervous system, acting as a substitute for glucose, on which these cells normally survive. The occurrence of high levels of ketones in the blood during starvation, a low carbohydrate diet, prolonged heavy exercise and uncontrolled type 1 diabetes mellitus is known as ketosis, and, in its extreme form, in out-of-control type 1 diabetes mellitus, as ketoacidosis.
Essential fatty acid
Fish is the main source of the longer omega-3 fats; eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), though they initially acquire these fats through the consumption of algae and seaweed. Some plant-based foods contain omega-3 in the form of alpha-linolenic acid (ALA), which appears to have a modest benefit for cardiovascular health. The human body can (and in case of a purely vegetarian diet often must unless certain algae or supplements derived from them are consumed) convert ALA to EPA and subsequently DHA. This elongation of ALA is inefficient. Conversion to DHA is higher in women than in men; this is thought to reflect the need to provide DHA to the fetus and infant during pregnancy and breast feeding.
Essential fatty acid
Essential fatty acids, or EFAs, are fatty acids that humans and other animals must ingest because the body requires them for good health but cannot synthesize them.
Ricinoleic acid
Ricinoleic acid, formally called 12-hydroxy-9-"cis"-octadecenoic acid is a fatty acid. It is an unsaturated omega-9 fatty acid and a hydroxy acid. It is a major component of the seed oil obtained from mature Castor plant ("Ricinus communis" L., Euphorbiaceae) seeds or in sclerotium of ergot ("Claviceps purpurea" Tul., Clavicipitaceae). About 90% of the fatty acid content in castor oil is the triglyceride formed from ricinoleic acid.
Linolenic acid
Linolenic acid is a type of fatty acid. It can refer to either of two octadecatrienoic acids (i.e. with an 18-carbon chain and three double bonds, which are found in the "cis" configuration), or a mixture of the two. Linolenate (in the form of triglyceride esters of linolenic acid) is often found in vegetable oils; traditionally, such fatty acylates are reported as the fatty acids:
Alpha-Eleostearic acid
α-Eleostearic acid or (9"Z",11"E",13"E")-octadeca-9,11,13-trienoic acid, is an organic compound, a conjugated fatty acid and one of the isomers of octadecatrienoic acid. It is often called simply eleostearic acid although there is also a β-eleostearic acid (the all-"trans" or (9"E",11"E",13"E") isomer). Its high degree of unsaturation gives tung oil its properties as a drying oil.
Essential fatty acid
Humans can convert both LA and ALA to docosapentaenoic acid (22:5n-6; DPA) and docosahexaenoic acid (22:6n-3; DHA) respectively, although the conversion to DHA is limited, resulting in lower blood levels of DHA than through direct ingestion. This is illustrated by studies in vegans and vegetarians. If there is relatively more LA than ALA in the diet it favors the formation of DPA from LA rather than DHA from ALA. This effect can be altered by changing the relative ratio of LA:ALA, but is more effective when total intake of polyunsaturated fatty acids is low. However, the capacity to convert LA to AA and ALA to DHA in the preterm infant is limited, and preformed AA and DHA may be required to meet the needs of the developing brain. Both AA and DHA are present in breastmilk and contribute along with the parent fatty acids LA and ALA to meeting the requirements of the newborn infant. Many infant formulas have AA and DHA added to them with an aim to make them more equivalent to human milk.
Palmitoleic acid
Palmitoleic acid, or (9"Z")-hexadec-9-enoic acid, is an omega-7 monounsaturated fatty acid with the formula CH(CH)CH=CH(CH)COOH that is a common constituent of the glycerides of human adipose tissue. It is present in all tissues but, in general, found in higher concentrations in the liver. It is biosynthesized from palmitic acid by the action of the enzyme Stearoyl-CoA desaturase-1.
Fatty acyl-CoA esters
Fatty acyl-CoA esters are fatty acid derivatives formed of one fatty acid, a 3'-phospho-AMP linked to phosphorylated pantothenic acid (Vitamin B) and cysteamine. 
Long-chain acyl-CoA esters are substrates for a number of important enzymatic reactions and play a central role in the regulation of metabolism as allosteric regulators of several enzymes. To participate in specific metabolic processes, fatty acids must first be activated by being joined in thioester linkage (R-CO-SCoA) to the -SH group of coenzyme A, where R is a fatty carbon chain. The thioester bond is a high energy bond.
Randle cycle
Fatty acids may act directly upon the pancreatic β-cell to regulate glucose-stimulated insulin secretion. This effect is biphasic. Initially fatty acids potentiate the effects of glucose. After prolonged exposure to high fatty acid concentrations this changes to an inhibition. Randle suggested that the term fatty acid syndrome would be appropriate to apply to the biochemical syndrome resulting from the high concentration of fatty acids and the relationship to abnormalities of carbohydrate metabolism, including starvation, diabetes and Cushing’s syndrome.
Fatty acid
Fatty acids do not show a great variation in their acidities, as indicated by their respective p"K". Nonanoic acid, for example, has a p"K" of 4.96, being only slightly weaker than acetic acid (4.76). As the chain length increases, the solubility of the fatty acids in water decreases, so that the longer-chain fatty acids have minimal effect on the pH of an aqueous solution. Even those fatty acids that are insoluble in water will dissolve in warm ethanol, and can be titrated with sodium hydroxide solution using phenolphthalein as an indicator. This analysis is used to determine the free fatty acid content of fats; i.e., the proportion of the triglycerides that have been hydrolyzed.
Decanoic acid
Decanoic acid, also known as capric acid (C10:0) or decylic acid, is a saturated fatty acid. Its formula is CH(CH)COOH. Salts and esters of decanoic acid are called decanoates or caprates. The term capric acid is derived from the Latin ""caper / capra"" (goat) because the sweaty, unpleasant smell of the compound is reminiscent of goats.
Alpha-Linolenic acid
α-Linolenic acid is a carboxylic acid with an 18-carbon chain and three "cis" double bonds. The first double bond is located at the third carbon from the methyl end of the fatty acid chain, known as the "n" end. Thus, α-linolenic acid is a polyunsaturated "n"−3 (omega-3) fatty acid. It is an isomer of gamma-linolenic acid (GLA), a polyunsaturated "n"−6 (omega-6) fatty acid.
Fatty acid synthesis
In humans, fatty acids are formed from carbohydrates predominantly in the liver and adipose tissue, as well as in the mammary glands during lactation.
Fatty acid synthesis
The main fuel stored in the bodies of animals is fat. The young adult human's fat stores average between about 10–20 kg, but varies greatly depending on age, gender, and individual disposition. By contrast the human body stores only about 400 g of glycogen, of which 300 g is locked inside the skeletal muscles and is unavailable to the body as a whole. The 100 g or so of glycogen stored in the liver is depleted within one day of starvation. Thereafter the glucose that is released into the blood by the liver for general use by the body tissues, has to be synthesized from the glucogenic amino acids and a few other gluconeogenic substrates, which do not include fatty acids.
Fatty acid
Fatty acids with an odd number of carbon atoms are called odd-chain fatty acids, whereas the rest are even-chain fatty acids. The difference is relevant to gluconeogenesis.
Fatty acid synthesis
Fatty acids are broken down to acetyl-CoA by means of beta oxidation inside the mitochondria, whereas fatty acids are synthesized from acetyl-CoA outside the mitochondrion, in the cytosol. The two pathways are distinct, not only in where they occur, but also in the reactions that occur, and the substrates that are used. The two pathways are mutually inhibitory, preventing the acetyl-CoA produced by beta-oxidation from entering the synthetic pathway via the acetyl-CoA carboxylase reaction. It can also not be converted to pyruvate as the pyruvate decarboxylation reaction is irreversible. Instead it condenses with oxaloacetate, to enter the citric acid cycle. During each turn of the cycle, two carbon atoms leave the cycle as CO in the decarboxylation reactions catalyzed by isocitrate dehydrogenase and alpha-ketoglutarate dehydrogenase. Thus each turn of the citric acid cycle oxidizes an acetyl-CoA unit while regenerating the oxaloacetate molecule with which the acetyl-CoA had originally combined to form citric acid. The decarboxylation reactions occur before malate is formed in the cycle. This is the only substance that can be removed from the mitochondrion to enter the gluconeogenic pathway to form glucose or glycogen in the liver or any other tissue. There can therefore be no net conversion of fatty acids into glucose.
Phosphatidic acid
Phosphatidic acids are phospholipids which on hydrolysis give rise to one molecule each of glycerol and phosphoric acid and two molecules of fatty acids. They constitute about 0.25% of phospholipids in the bilayer.
Fat
There are many different kinds of fats, but each is a variation on the same chemical structure. All fats are derivatives of fatty acids and glycerol. Most fats are glycerides, particularly triglycerides (triesters of glycerol). One chain of fatty acid is bonded to each of the three -OH groups of the glycerol by the reaction of the carboxyl end of the fatty acid (-COOH) with the alcohol; I.e. three chains per molecule. Water is eliminated and the carbons are linked by an -O- bond through dehydration synthesis. This process is called esterification and fats are therefore esters. As a simple visual illustration, if the kinks and angles of these chains were straightened out, the molecule would have the shape of a capital letter E. The fatty acids would each be a horizontal line; the glycerol "backbone" would be the vertical line that joins the horizontal lines. Fats therefore have "ester" bonds.
Lacceroic acid
Lacceroic acid (or dotriacontanoic acid) is a saturated fatty acid.
Lipid
Beta oxidation is the metabolic process by which fatty acids are broken down in the mitochondria or in peroxisomes to generate acetyl-CoA. For the most part, fatty acids are oxidized by a mechanism that is similar to, but not identical with, a reversal of the process of fatty acid synthesis. That is, two-carbon fragments are removed sequentially from the carboxyl end of the acid after steps of dehydrogenation, hydration, and oxidation to form a beta-keto acid, which is split by thiolysis. The acetyl-CoA is then ultimately converted into ATP, CO, and HO using the citric acid cycle and the electron transport chain. Hence the citric acid cycle can start at acetyl-CoA when fat is being broken down for energy if there is little or no glucose available. The energy yield of the complete oxidation of the fatty acid palmitate is 106 ATP. Unsaturated and odd-chain fatty acids require additional enzymatic steps for degradation.
Fatty acid
In animals, fatty acids are formed from carbohydrates predominantly in the liver, adipose tissue, and the mammary glands during lactation.
Cat food
Fatty acids are an important part of the cats diet, some are more important than others with respect to the cats diet and these are known as essential fatty acids. Essential fatty acids are nutrients that cats are unable to produce at all or in sufficient amounts to reach their needs. There are 3 essential fatty acids that should be included in a cats diets and they are: Alpha-Linolenic acid, Linoleic acid, and Arachidonic acid. Alpha-Linolenic acid is an Omega–3 fatty acid that is important to cats as it aids in the maintenance of their skin's water barrier. As the water barrier is important to the cats skin, ingredients that are high in Alpha-Linolenic acid, such as flaxseed, should be included in the cats diet. Another source of Omega-3 s are in fish oil however, it is higher in Eicosapentaenoic acid (EPA) and Docosahexaenoic acid (DHA) which can be important for cats as they have anti-inflammatory properties. Linoleic acid is an example of an Omega-6 fatty acid that also helps with the health of the cat's skin by maintaining the integrity of their epithelial tissues. Linoleic acid is commonly found in plant-based oils, an ingredient that is commonly used as a source of Linoleic acid is sunflower oil. Arachidonic acid is also essential to cats because they are unable to create it from linoleic acid due to an absence of the Delta 6 desaturase enzyme. It's important for their skin for the same reason as Linoleic acid and can be found in ingredients such as animal fat.
Fatty acid
Fatty acids that are required for good health but cannot be made in sufficient quantity from other substrates, and therefore must be obtained from food, are called essential fatty acids. There are two series of essential fatty acids: one has a double bond three carbon atoms away from the methyl end; the other has a double bond six carbon atoms away from the methyl end. Humans lack the ability to introduce double bonds in fatty acids beyond carbons 9 and 10, as counted from the carboxylic acid side. Two essential fatty acids are linoleic acid (LA) and alpha-linolenic acid (ALA). These fatty acids are widely distributed in plant oils. The human body has a limited ability to convert ALA into the longer-chain omega-3 fatty acids — eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which can also be obtained from fish. Omega-3 and omega-6 fatty acids are biosynthetic precursors to endocannabinoids with antinociceptive, anxiolytic, and neurogenic properties.
Metabolism
Fatty acids are made by fatty acid synthases that polymerize and then reduce acetyl-CoA units. The acyl chains in the fatty acids are extended by a cycle of reactions that add the acyl group, reduce it to an alcohol, dehydrate it to an alkene group and then reduce it again to an alkane group. The enzymes of fatty acid biosynthesis are divided into two groups: in animals and fungi, all these fatty acid synthase reactions are carried out by a single multifunctional type I protein, while in plant plastids and bacteria separate type II enzymes perform each step in the pathway.
Fatty acid synthesis
In mammals the aerobic desaturation is catalyzed by a complex of three membrane-bound enzymes ("NADH-cytochrome b reductase, cytochrome b", and a "desaturase"). These enzymes allow molecular oxygen, O, to interact with the saturated fatty acyl-CoA chain, forming a double bond and two molecules of water, HO. Two electrons come from NADH + H and two from the single bond in the fatty acid chain. These mammalian enzymes are, however, incapable of introducing double bonds at carbon atoms beyond C-9 in the fatty acid chain..) Hence mammals cannot synthesize linoleate or linolenate (which have double bonds at the C-12 (= Δ), or the C-12 and C-15 (= Δ and Δ) positions, respectively, as well as at the Δ position), nor the polyunsaturated, 20-carbon arachidonic acid that is derived from linoleate. These are all termed essential fatty acids, meaning that they are required by the organism, but can only be supplied via the diet. (Arachidonic acid is the precursor the prostaglandins which fulfill a wide variety of functions as local hormones.)
Saturation (chemistry)
The term saturation is applied similarly to the fatty acid constituents of fats, which can be either saturated or unsaturated, depending on whether the constituent fatty acids contain carbon-carbon double bonds. Tallow consists mainly of triglycerides (fats), whose major constituents are derived from the saturated stearic and monounsaturated oleic acids. Many vegetable oils contain fatty acids with one ("monounsaturated") or more ("polyunsaturated") double bonds in them.
Olive oil acidity
Free acidity is an important parameter that defines the quality of olive oil and is defined as a percentage as grams of free fatty acids (expressed as oleic acid, the main fatty acid present in olive oil) in 100 grams of oil. As defined by the European Commission regulation No. 2568/91 and subsequent amendments, the highest quality olive oil (Extra-Virgin olive oil) must feature a free acidity lower than 0.8%. Virgin olive oil is characterized by acidity between 0.8% and 2%, while lampante olive oil (a low quality oil that is not edible) features a free acidity higher than 2%. The increase of free acidity in olive oil is due to free fatty acids that are released from triglycerides.
Essential fatty acid
In the body, essential fatty acids serve multiple functions. In each of these, the balance between dietary ω-3 and ω-6 strongly affects function.
Fatty acids are straight chain hydrocarbons possessing a carboxyl (COOH) group at one end. The carbon next to the carboxylate is known as α, the next carbon β, and so forth. Since biological fatty acids can be of different lengths, the last position is labelled as a "ω", the last letter in the Greek alphabet. The physiological properties of unsaturated fatty acids largely depend on the position of the first unsaturation relative to the end position and not the carboxylate. For example, the term ω-3 signifies that the first double bond exists as the third carbon-carbon bond from the terminal CH end (ω) of the carbon chain. The number of carbons and the number of double bonds are also listed.
Fatty acid
When metabolized, fatty acids yield large quantities of ATP. Many cell types can use either glucose or fatty acids for this purpose. Fatty acids (provided either by ingestion or by drawing on triglycerides stored in fatty tissues) are distributed to cells to serve as a fuel for muscular contraction and general metabolism. They are broken down to CO and water by the intra-cellular mitochondria, releasing large amounts of energy, captured in the form of ATP through beta oxidation and the citric acid cycle.
Omega-9 fatty acid
Omega-9 fatty acids (ω−9 fatty acids or "n"−9 fatty acids) are a family of unsaturated fatty acids which have in common a final carbon–carbon double bond in the omega−9 position; that is, the ninth bond from the methyl end of the fatty acid.
Natural product
One molecule of acetyl-CoA (the "starter unit") and several molecules malonyl-CoA (the "extender units") are condensed by fatty acid synthase to produce fatty acids. Fatty acid are essential components of lipid bilayers that form cell membranes as well as fat energy stores in animals.
Fatty-acyl-CoA synthase
Synthesis of fatty acids is generally performed by fatty acid synthase (FAS). Though the syntheses of fatty acids are very similar across all organisms, the enzymes and subsequent enzymatic mechanisms involved in fatty acid synthesis vary between eukaryotes and prokaryotes. There are two types of fatty acid synthesis (FAS) mechanisms: type I FAS and type II FAS. Type I FAS exists in eukaryotes, including mammalian cells and fungi. Type II FAS are found in prokaryotes. The type I FAS system utilizes a multi-enzyme complex, which are highly integrated, while the type II FAS system utilizes individual, separate enzymes to catalyze the reactions involved in fatty acid synthesis. Yeast fatty acyl synthase belongs to the Type I FAS and was the first of Type I FAS to be studied.
Eicosapentaenoic acid
Eicosapentaenoic acid (EPA; also icosapentaenoic acid) is an omega-3 fatty acid. In physiological literature, it is given the name 20:5(n-3). It also has the trivial name timnodonic acid. In chemical structure, EPA is a carboxylic acid with a 20-carbon chain and five "cis" double bonds; the first double bond is located at the third carbon from the omega end.
Essential fatty acid
Mammals lack the ability to introduce double bonds in fatty acids beyond carbon 9 and 10, hence ω-6 linoleic acid (18:2,9,12), abbreviated LA (18:2n-6), and the ω-3 linolenic acid (18:3,9,12,15), abbreviated ALA (18:3n-3), are essential for humans in the diet. In humans, arachidonic acid (20:4,5,8,11,14, abbreviated 20:4n-6) can be synthesized from LA by alternative desaturation and chain elongation.
Heneicosylic acid
Heneicosylic acid, or "heneicosanoic acid", is a 21-carbon long-chain saturated fatty acid with the chemical formula CH(CH)COOH. It has shown relevance in the production of foams, paints, and related viscous materials.
Phytanic acid
Phytanic acid (or 3,7,11,15-tetramethyl hexadecanoic acid) is a branched chain fatty acid that humans can obtain through the consumption of dairy products, ruminant animal fats, and certain fish. Western diets are estimated to provide 50–100 mg of phytanic acid per day. In a study conducted in Oxford, individuals who consumed meat had, on average, a 6.7-fold higher geometric mean plasma phytanic acid concentration than did vegans.
Unlike most fatty acids, phytanic acid cannot be metabolized by β-oxidation. Instead, it undergoes α-oxidation in the peroxisome, where it is converted into pristanic acid by the removal of one carbon. Pristanic acid can undergo several rounds of β-oxidation in the peroxisome to form medium chain fatty acids that can be converted to carbon dioxide and water in mitochondria.
Saturated fat
In 2003, the World Health Organization (WHO) and Food and Agriculture Organization (FAO) expert consultation report concluded that "intake of saturated fatty acids is directly related to cardiovascular risk. The traditional target is to restrict the intake of saturated fatty acids to less than 10% of daily energy intake and less than 7% for high-risk groups. If populations are consuming less than 10%, they should not increase that level of intake. Within these limits, intake of foods rich in myristic and palmitic acids should be replaced by fats with a lower content of these particular fatty acids. In developing countries, however, where energy intake for some population groups may be inadequate, energy expenditure is high and body fat stores are low (BMI <18.5 kg/m). The amount and quality of fat supply has to be considered keeping in mind the need to meet energy requirements. Specific sources of saturated fat, such as coconut and palm oil, provide low-cost energy and may be an important source of energy for the poor."
Arbuscular mycorrhiza
Specific organismal chemical signatures can be used to detect biomass of more cryptic organisms, such as AM fungi or soil bacteria. Lipids, more specifically phospholipids and neutral lipids, contain fatty acids connected to a glycerol backbone. The fatty acid composition of organisms varies, and the proportions of specific fatty acids can be organism specific. For example, in AM fungi the proportion of the fatty acids, 16:1ω5 and 18:1ω7, in the phospholipid portion account for approximately 58% of total fatty acid composition. The fatty acid, 16:1ω5 is the most commonly used acid to characterize AM fungi in soils and can be used as a strong indicator of mycelial biomass in soil sample.
Essential fatty acid interactions
Arachidonic acid (AA) is a 20-carbon ω-6 conditionally essential fatty acid. It sits at the head of the "arachidonic acid cascade" – more than 20 different signalling paths that control a wide array of bodily functions, but especially those functions involving inflammation, cell growth and the central nervous system. Most AA in the human body derives from dietary linoleic acid (another essential fatty acid, 18:2 ω-6), which is derived from nuts, seeds, vegetable oils and animal fats.
Fatty acid synthesis
The branched-chain fatty acid synthesizing system uses α-keto acids as primers. This system is distinct from the branched-chain fatty acid synthetase that utilizes short-chain acyl-CoA esters as primers. α-Keto acid primers are derived from the transamination and decarboxylation of valine, leucine, and isoleucine to form 2-methylpropanyl-CoA, 3-methylbutyryl-CoA, and 2-Methylbutyryl-CoA, respectively. 2-Methylpropanyl-CoA primers derived from valine are elongated to produce even-numbered iso-series fatty acids such as 14-methyl-pentadecanoic (isopalmitic) acid, and 3-methylbutyryl-CoA primers from leucine may be used to form odd-numbered iso-series fatty acids such as 13-methyl-tetradecanoic acid. 2-Methylbutyryl-CoA primers from isoleucine are elongated to form anteiso-series fatty acids containing an odd number of carbon atoms such as 12-Methyl tetradecanoic acid. Decarboxylation of the primer precursors occurs through the branched-chain α-keto acid decarboxylase (BCKA) enzyme. Elongation of the fatty acid follows the same biosynthetic pathway in "Escherichia coli" used to produce straight-chain fatty acids where malonyl-CoA is used as a chain extender. The major end products are 12–17 carbon branched-chain fatty acids and their composition tends to be uniform and characteristic for many bacterial species.
Fat
Some fatty acids that are set free by the digestion of fats are called essential because they cannot be synthesized in the body from simpler constituents. There are two essential fatty acids (EFAs) in human nutrition: alpha-linolenic acid (an omega-3 fatty acid) and linoleic acid (an omega-6 fatty acid). Other lipids needed by the body can be synthesized from these and other fats. Fats and other lipids are broken down in the body by enzymes called lipases produced in the pancreas.
ACADM
The LCAD enzyme catalyzes most of fatty acid beta-oxidation by forming a C2-C3 trans-double bond in the fatty acid. MCAD works on long-chain fatty acids, typically between C4 and C12-acylCoA. Fatty acid oxidation has proven to spare glucose in fasting conditions, and is also required for amino acid metabolism, which is essential for the maintenance of adequate glucose production.
Heptacosylic acid
Heptacosylic acid, or heptacosanoic acid or carboceric acid, is a 27-carbon long-chain saturated fatty acid with the chemical formula CH(CH)COOH.
Cat food
A fat is a type of lipid which comes in the form of many different molecules throughout the body, and fatty acids are just one type of fat that can be found. 
Fatty acids come in a variety of molecular shapes, sizes and chemical compositions. They can also be divided into many different categories. Fatty acids can become attached to different molecules like carbohydrates or proteins and can elicit a wide range of functions in the body. Some of those functions include: providing long-term energy storage, insulation (prevents heat loss, protects vital organs, helps transmit nerve impulses faster), structure, transportation around the body for nutrients and other biological molecules, and can also be precursors to other compounds in the body such as hormones (some of which are important for gut/immune/overall health). The length, degree of saturation and configuration of a fatty acid affects how it is broken down, absorbed and utilized in the gastrointestinal tract (GIT).
Furan fatty acids
Furan fatty acids are a group of fatty acids that contain a furan ring. To this furan ring, an unbranched carboxylic acid and, at another position, an alkyl residue are attached. Natural furan fatty acids are mono- or di-methylated on the furan ring. Furan fatty acids are can be found in a variety of plant and animal species.
Omega-7 fatty acid
Omega-7 fatty acids are a class of unsaturated fatty acids in which the site of unsaturation is seven carbon atoms from the end of the carbon chain. The two most common omega-7 fatty acids in nature are palmitoleic acid and vaccenic acid.
Sapienic acid
Sapienic acid (16:1, n-10, cis-6 hexadecenoic, or sapienate) is a fatty acid that is a major component of human sebum. Sapienic acid is a sebum fatty acid that is unique to humans (from whose scientific name it takes the root "sapiens"). The equivalent fatty acid in mouse sebum is palmitoleic acid. Sapienic acid has been implicated in the development of acne, and it may have potent antibacterial activity.
Lipid-anchored protein
Fatty acylated proteins are proteins that have been post-translationally modified to include the covalent attachment of fatty acids at certain amino acid residues. The most common fatty acids that are covalently attached to the protein are the saturated myristic (14-carbon) acid and palmitic acid (16-carbon). Proteins can be modified to contain either one or both of these fatty acids.
Nonadecylic acid
Nonadecylic acid, or nonadecanoic acid, is a 19-carbon long saturated fatty acid with the chemical formula CH(CH)COOH. It forms salts called "nonadecylates". Nonadecylic acid can be found in fats and vegetable oils. It is also used by insects as pheromones.
Triglyceride
The three fatty acids (RCOH, R′COH, R″COH in the above equation) are usually different, but many kinds of triglycerides are known. The chain lengths of the fatty acids in naturally occurring triglycerides vary, but most contain 16, 18, or 20 carbon atoms. Natural fatty acids found in plants and animals are typically composed of only even numbers of carbon atoms, reflecting the pathway for their biosynthesis from the two-carbon building-block acetyl CoA. Bacteria, however, possess the ability to synthesise odd- and branched-chain fatty acids. As a result, ruminant animal fat contains odd-numbered fatty acids, such as 15, due to the action of bacteria in the rumen. Many fatty acids are unsaturated, some are polyunsaturated (e.g., those derived from linoleic acid).
Lauric acid
Lauric acid or systematically, dodecanoic acid, is a saturated fatty acid with a 12-carbon atom chain, thus having many properties of medium-chain fatty acids, is a bright white, powdery solid with a faint odor of bay oil or soap. The salts and esters of lauric acid are known as laurates.
Essential fatty acid
Reference intake values for as published by the Panel on Dietetic Products, Nutrition and Allergies of the European Food Safety Authority (EFSA).
In the United States, the recommendations for omega-3 fatty acids covers ALA, EPA and DHA, and for adults the values are 1.6 g/day for men and 1.1. g/day for women. The recommendation for omega-6 fatty acids is for linoleic acid: 17 g/day for younger men, dropping to 14 g/day for older men; for women 12 and 11 g/day.
Biomolecule
Lipids (oleaginous) are chiefly fatty acid esters, and are the basic building blocks of biological membranes. Another biological role is energy storage (e.g., triglycerides). Most lipids consist of a polar or hydrophilic head (typically glycerol) and one to three nonpolar or hydrophobic fatty acid tails, and therefore they are amphiphilic. Fatty acids consist of unbranched chains of carbon atoms that are connected by single bonds alone (saturated fatty acids) or by both single and double bonds (unsaturated fatty acids). The chains are usually 14-24 carbon groups long, but it is always an even number.
Human nutrition
A molecule of dietary fat typically consists of several fatty acids (containing long chains of carbon and hydrogen atoms), bonded to a glycerol. They are typically found as triglycerides (three fatty acids attached to one glycerol backbone). Fats may be classified as saturated or unsaturated depending on the chemical structure of the fatty acids involved. Saturated fats have all of the carbon atoms in their fatty acid chains bonded to hydrogen atoms, whereas unsaturated fats have some of these carbon atoms double-bonded, so their molecules have relatively fewer hydrogen atoms than a saturated fatty acid of the same length. Unsaturated fats may be further classified as monounsaturated (one double-bond) or polyunsaturated (many double-bonds). Furthermore, depending on the location of the double-bond in the fatty acid chain, unsaturated fatty acids are classified as omega-3 or omega-6 fatty acids. Trans fats are a type of unsaturated fat with "trans"-isomer bonds; these are rare in nature and in foods from natural sources; they are typically created in an industrial process called (partial) hydrogenation.
Fatty acid
Short- and medium-chain fatty acids are absorbed directly into the blood via intestine capillaries and travel through the portal vein just as other absorbed nutrients do. However, long-chain fatty acids are not directly released into the intestinal capillaries. Instead they are absorbed into the fatty walls of the intestine villi and reassembled again into triglycerides. The triglycerides are coated with cholesterol and protein (protein coat) into a compound called a chylomicron.
Lipid metabolism
In the cytosol of the cell (for example a muscle cell), the glycerol will be converted to glyceraldehyde 3-phosphate, which is an intermediate in the glycolysis, to get further oxidized and produce energy. However, the main steps of fatty acids catabolism occur in the mitochondria. Long chain fatty acids (more than 14 carbon) need to be converted to Fatty acyl-CoA in order to pass across the mitochondria membrane. Fatty acid catabolism begins in the cytoplasm of cells as Acyl-CoA synthetase uses the energy from cleavage of an ATP to catalyze the addition of Coenzyme A to the fatty acid. The resulting Acyl-CoA cross the mitochondria membrane and enter the process of beta oxidation. The main products of the beta oxidation pathway are Acetyl-CoA (which is used in the Citric acid cycle to produce energy), NADH and FADH. The process of beta oxidation requires the following enzymes: Acyl CoA dehydrogenase, Enoyl-CoA hydratase, 3-hydroxyacyl-CoA dehydrogenase, and 3-ketoacyl-CoA thiolase. The diagram to the left shows how fatty acids are converted into Acetyl-coA. The overall net reaction, using palmitoyl CoA (16:0) as a model substrate is:
Omega-3 fatty acid
Omega−3 fatty acids, also called ω−3 fatty acids or "n"−3 fatty acids, are polyunsaturated fatty acids (PUFAs) characterized by a double bond three atoms away from the terminal methyl group. They are widely distributed in nature, being important constituents of animal lipid metabolism, and they play an important role in the human diet and in human physiology. The three types of omega−3 fatty acids involved in human physiology are α-linolenic acid (ALA), found in plant oils, and eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), both commonly found in marine oils. Marine algae and phytoplankton are primary sources of omega−3 fatty acids. Common sources of plant oils containing ALA include walnut, edible seeds, clary sage seed oil, algal oil, flaxseed oil, Sacha Inchi oil, "Echium" oil, and hemp oil, while sources of animal omega−3 fatty acids EPA and DHA include fish, fish oils, eggs from chickens fed EPA and DHA, squid oils, and krill oil.
Omega−3 fatty acids are important for normal metabolism. Mammals are unable to synthesize omega−3 fatty acids, but can obtain the shorter-chain omega−3 fatty acid ALA (18 carbons and 3 double bonds) through diet and use it to form the more important long-chain omega−3 fatty acids, EPA (20 carbons and 5 double bonds) and then from EPA, the most crucial, DHA (22 carbons and 6 double bonds). The ability to make the longer-chain omega−3 fatty acids from ALA may be impaired in aging. In foods exposed to air, unsaturated fatty acids are vulnerable to oxidation and rancidity. Dietary supplementation with omega−3 fatty acids does not appear to affect the risk of death, cancer or heart disease. Furthermore, fish oil supplement studies have failed to support claims of preventing heart attacks or strokes or any vascular disease outcomes.
The terms "ω–3 ("omega–3") fatty acid" and "n–"3 "fatty acid" are derived from organic nomenclature. One way in which a fatty acid is named is determined by the location of the first double bond, counted from the methyl end, that is, the omega (ω-) or the "n"- end (see illustration). In general terminology using either "n–x" or ω–"x", the dash is a minus sign (although it is never read as such), and the number "n–x" (or ω–"x") refers to the locant of the double bond linking two carbon atoms. Thus, in omega"–"3 fatty acids in particular, there is a double bond located on the carbon numbered 3 lower than the highest carbon number. By example, α-linolenic acid (ALA; illustration) is an 18-carbon chain having three double bonds, the first being located at the third carbon from the methyl end of the fatty acid chain, known as the "n" end. Thus, α-linolenic acid is a polyunsaturated "n−3" (omega-3) fatty acid with lipid number, 18:3 (18 carbon atoms, 3 double bonds).
Fatty acid
Fatty acids are usually produced industrially by the hydrolysis of triglycerides, with the removal of glycerol (see oleochemicals). Phospholipids represent another source. Some fatty acids are produced synthetically by hydrocarboxylation of alkenes.
Fatty acid metabolism
Fatty acids, stored as triglycerides in an organism, are an important source of energy because they are both reduced and anhydrous. The energy yield from a gram of fatty acids is approximately 9 kcal (37 kJ), compared to 4 kcal (17 kJ) for carbohydrates. Since the hydrocarbon portion of fatty acids is hydrophobic, these molecules can be stored in a relatively anhydrous (water-free) environment. Carbohydrates, on the other hand, are more highly hydrated. For example, 1 g of glycogen can bind approximately 2 g of water, which translates to 1.33 kcal/g (4 kcal/3 g). This means that fatty acids can hold more than six times the amount of energy per unit of storage mass. Put another way, if the human body relied on carbohydrates to store energy, then a person would need to carry 31 kg (67.5 lb) of hydrated glycogen to have the energy equivalent to 4.6 kg (10 lb) of fat.
Fat
Saturated fats can stack themselves in a closely packed arrangement, so they can solidify easily and are typically solid at room temperature. For example, animal fats tallow and lard are high in saturated fatty acid content and are solids. Olive and linseed oils on the other hand are unsaturated and liquid. Fats serve both as energy sources for the body, and as stores for energy in excess of what the body needs immediately. Each gram of fat when burned or metabolized releases about 9 food calories (37 kJ = 8.8 kcal). Fats are broken down in the healthy body to release their constituents, glycerol and fatty acids. Glycerol itself can be converted to glucose by the liver and so become a source of energy.
Fatty acid metabolism
A significant proportion of the fatty acids in the body are obtained from the diet, in the form of triglycerides of either animal or plant origin. The fatty acids in the fats obtained from land animals tend to be saturated, whereas the fatty acids in the triglycerides of fish and plants are often polyunsaturated and therefore present as oils.
Lipotoxicity
An excess of free fatty acids in liver cells plays a role in Nonalcoholic Fatty Liver Disease (NAFLD). In the liver, it is the type of fatty acid, not the quantity, that determines the extent of the lipotoxic effects. In hepatocytes, the ratio of monounsaturated fatty acids and saturated fatty acids leads to apoptosis and liver damage. There are several potential mechanisms of by which the excess fatty acids can cause cell death and damage. They may activate death receptors, stimulate apoptotic pathways, or initiate cellular stress response in the endoplasmic reticulum. These lipotoxic effects have been shown to be prevented by the presence of excess triglycerides within the hepatocytes.
Lipotoxicity in cardiac tissue is attributed to excess saturated fatty acids. The apoptosis that follows is believed to be caused by unfolded protein response in the endoplasmic reticulum. Researchers are working on treatments that will increase the oxidation of these fatty acids within the heart in order to prevent the lipotoxic effects.
Fatty acid metabolism
The pyruvate produced by glycolysis is an important intermediary in the conversion of carbohydrates into fatty acids and cholesterol. This occurs via the conversion of pyruvate into acetyl-CoA in the mitochondrion. However, this acetyl CoA needs to be transported into cytosol where the synthesis of fatty acids and cholesterol occurs. This cannot occur directly. To obtain cytosolic acetyl-CoA, citrate (produced by the condensation of acetyl CoA with oxaloacetate) is removed from the citric acid cycle and carried across the inner mitochondrial membrane into the cytosol. There it is cleaved by ATP citrate lyase into acetyl-CoA and oxaloacetate. The oxaloacetate is returned to mitochondrion as malate (and then converted back into oxaloacetate to transfer more acetyl-CoA out of the mitochondrion). The cytosolic acetyl-CoA is carboxylated by acetyl CoA carboxylase into malonyl CoA, the first committed step in the synthesis of fatty acids.
Total fatty matter
Total fatty matter (TFM) is one of the most important characteristics describing the quality of soap and it is always specified in commercial transactions. It is defined as the total amount of fatty matter, mostly fatty acids, that can be separated from a sample after splitting with mineral acid, usually hydrochloric acid. The fatty acids most commonly present in soap are oleic, stearic and palmitic acids and pure, dry, sodium oleate has TFM 92.8%, while top quality soap noodles now increasingly used for making soap tablets in small and medium size factories, are typically traded with a specification TFM 78% min., moisture 14% max. But besides moisture, finished commercial soap, especially laundry soap, and also contains fillers used to lower its cost or confer special properties, plus emollients, preservatives, etc. and then the TFM can be as low as 50%. Fillers, which are usually dry powders, also make the soap harder, harsher on the skin and with greater tendency to become 'mushy' in water and so low TFM is usually associated with hardness and lower quality. In older days in Europe and in some countries now, soap with TFM 75% minimum was referred to as Grade 1 and 65% minimum as Grade 2 and less 60% as Grade 3.
Cerotic acid
Cerotic acid, or "hexacosanoic acid", is a 26-carbon long-chain saturated fatty acid with the chemical formula CH(CH)COOH. It is most commonly found in beeswax and carnauba wax, and is a white crystalline solid.
Omega-3 fatty acid
Although "n" and ω (omega) are synonymous, the IUPAC recommends that "n" be used to identify the highest carbon number of a fatty acid. The more common name – omega"–"3 fatty acid – is used in both the lay media and scientific literature.
Carboxylic acid
A carboxylic acid is an organic compound that contains a carboxyl group (C(=O)OH). The general formula of a carboxylic acid is R–COOH, with R referring to the rest of the (possibly quite large) molecule. Carboxylic acids occur widely and include the amino acids (which make up proteins) and acetic acid (which is part of vinegar and occurs in metabolism).
Tumor metabolome
Fatty acid synthesis is an anabolic process that starts from the conversion of acetyl-CoA to malonyl-CoA by acetyl-CoA carboxylase. Malonyl CoA leads to fatty acid synthesis (FAS) and is involved in the elongation of fatty acids through Fatty acid synthase (FASN). Although aerobic glycolysis is the best documented metabolic phenotype of tumor cells, it is not a universal feature of all human cancers. Amino acids and fatty acids have been shown to function as fuels for tumor cells to proliferate. The carnitine palmitoyltransferase enzymes that regulate the β-oxidation of fatty acids may have a key role in determining some of these phenotypes. Enhanced fatty acid synthesis provides lipids for membrane biogenesis to tumor cells and hence, it gives advantage in both growth and survival of the cell.
Omega hydroxy acid
Omega hydroxy acids (also known as ω-hydroxy acids) are a class of naturally occurring straight-chain aliphatic organic acids "n" carbon atoms long with a carboxyl group at position 1 and a hydroxyl at terminal position "n" where "n" > 3. The C16 and C18 omega hydroxy acids 16-hydroxy palmitic acid and 18-hydroxy stearic acid are key monomers of cutin in the plant cuticle. The polymer cutin is formed by inter-esterification of omega hydroxy acids and derivatives of them that are substituted in mid-chain, such as 10,16-dihydroxy palmitic acid. Only the epidermal cells of plants synthesize cutin.
Myristic acid
Myristic acid (IUPAC systematic name: 1-tetradecanoic acid) is a common saturated fatty acid with the molecular formula CH(CH)COOH. Its salts and esters are commonly referred to as myristates. It is named after the binomial name for nutmeg ("Myristica fragrans"), from which it was first isolated in 1841 by Lyon Playfair.
Fatty acid
Saturated fatty acids have no C=C double bonds. They have the same formula CH(CH)COOH, with variations in "n". An important saturated fatty acid is stearic acid (n = 16), which when neutralized with lye is the most common form of soap.
Alpha-Linolenic acid
α-Linolenic acid (ALA) is an "n"−3 fatty acid. It is one of two essential fatty acids (the other being linoleic acid), so called because they are necessary for health and cannot be produced within the human body. They must be acquired through diet. ALA is an omega-3 fatty acid found in seeds (chia, flaxseed, hemp, see also table below), nuts (notably walnuts), and many common vegetable oils. In terms of its structure, it is named "all"-"cis"-9,12,15-octadecatrienoic acid. In physiological literature, it is listed by its lipid number, 18:3, and ("n"−3); its isomer GLA is 18:3 ("n"−6).
Nervonic acid
This acid is an important member of the group of the cerebrosides, which are fatty acids of the glycosphingolipids group, important components of the muscles and the central nervous system and peripheral. Indeed, it is one of the major fatty acids in brain sphingolipids, normally accounting for approximately 40% of the total fatty acids in sphingolipids.
Nutrition
Most fatty acids are non-essential, meaning the body can produce them as needed, generally from other fatty acids and always by expending energy to do so. However, in humans, at least two fatty acids are essential and must be included in the diet. An appropriate balance of essential fatty acids—omega-3 and omega-6 fatty acids—seems also important for health, although definitive experimental demonstration has been elusive. Both of these "omega" long-chain polyunsaturated fatty acids are substrates for a class of eicosanoids known as prostaglandins, which have roles throughout the human body. They are hormones, in some respects. The omega-3 eicosapentaenoic acid (EPA), which can be made in the human body from the omega-3 essential fatty acid alpha-linolenic acid (ALA), or taken in through marine food sources, serves as a building block for series 3 prostaglandins (e.g., weakly inflammatory PGE3). The omega-6 dihomo-gamma-linolenic acid (DGLA) serves as a building block for series 1 prostaglandins (e.g. anti-inflammatory PGE1), whereas arachidonic acid (AA) serves as a building block for series 2 prostaglandins (e.g. pro-inflammatory PGE 2). Both DGLA and AA can be made from the omega-6 linoleic acid (LA) in the human body, or can be taken in directly through food. An appropriately balanced intake of omega-3 and omega-6 partly determines the relative production of different prostaglandins, which is one reason why a balance between omega-3 and omega-6 is believed important for cardiovascular health. In industrialized societies, people typically consume large amounts of processed vegetable oils, which have reduced amounts of the essential fatty acids along with too much of omega-6 fatty acids relative to omega-3 fatty acids.
Saturated fat
A saturated fat is a type of fat in which the fatty acid chains have all or predominantly single bonds. A fat is made of two kinds of smaller molecules: glycerol and fatty acids. Fats are made of long chains of carbon (C) atoms. Some carbon atoms are linked by single bonds (-C-C-) and others are linked by double bonds (-C=C-). Double bonds can react with hydrogen to form single bonds. They are called saturated, because the second bond is broken and each half of the bond is attached to (saturated with) a hydrogen atom. Most animal fats are saturated. The fats of plants and fish are generally unsaturated. Saturated fats tend to have higher melting points than their corresponding unsaturated fats, leading to the popular understanding that saturated fats tend to be solids at room temperatures, while unsaturated fats tend to be liquid at room temperature with varying degrees of viscosity (meaning both saturated and unsaturated fats are found to be liquid at body temperature).
Essential fatty acid
In nonscientific writing, common usage is that the term "essential fatty acid" comprises all the ω-3 or -6 fatty acids. Conjugated fatty acids like calendic acid are not considered essential. Authoritative sources include the whole families, but generally only make dietary recommendations for LA and ALA with the exception of DHA for infants under the age of 6 months. Recent reviews by WHO/FAO in 2009 and the European Food Safety Authority have reviewed the evidence and made recommendations for minimal intakes of LA and ALA and have also recommended intakes of longer chain ω-3 fatty acids based on the association of oily fish consumption with a lower risk of cardiovascular disease. Some earlier review lumped all polyunsaturated fatty acids together without qualification whether they were short or long-chain PUFA or whether they were ω-3 and ω-6 PUFA.
Fatty acid
The concept of fatty acid ("acide gras") was introduced by Michel Eugène Chevreul, though he initially used some variant terms: "graisse acide" and "acide huileux" ("acid fat" and "oily acid").
Cell membrane
The fatty chains in phospholipids and glycolipids usually contain an even number of carbon atoms, typically between 16 and 20. The 16- and 18-carbon fatty acids are the most common. Fatty acids may be saturated or unsaturated, with the configuration of the double bonds nearly always "cis". The length and the degree of unsaturation of fatty acid chains have a profound effect on membrane fluidity as unsaturated lipids create a kink, preventing the fatty acids from packing together as tightly, thus decreasing the melting temperature (increasing the fluidity) of the membrane. The ability of some organisms to regulate the fluidity of their cell membranes by altering lipid composition is called homeoviscous adaptation.
Fatty acid ester
Fatty acid methyl esters (FAME) are esters of fatty acids. The physical characteristics of fatty acid esters are closer to those of fossil diesel fuels than pure vegetable oils, but properties depend on the type of vegetable oil. A mixture of different fatty acid methyl esters is commonly referred to as biodiesel, which is a renewable alternative fuel. FAME has physical properties similar to those of conventional diesel. It is also non-toxic and biodegradable.
Nutrition
A molecule of dietary fat typically consists of several fatty acids (containing long chains of carbon and hydrogen atoms), bonded to a glycerol. They are typically found as triglycerides (three fatty acids attached to one glycerol backbone). Fats may be classified as saturated or unsaturated depending on the detailed structure of the fatty acids involved. Saturated fats have all of the carbon atoms in their fatty acid chains bonded to hydrogen atoms, whereas unsaturated fats have some of these carbon atoms double-bonded, so their molecules have relatively fewer hydrogen atoms than a saturated fatty acid of the same length. Unsaturated fats may be further classified as monounsaturated (one double-bond) or polyunsaturated (many double-bonds). Furthermore, depending on the location of the double-bond in the fatty acid chain, unsaturated fatty acids are classified as omega-3 or omega-6 fatty acids. Trans fats are a type of unsaturated fat with "trans"-isomer bonds; these are rare in nature and in foods from natural sources; they are typically created in an industrial process called (partial) hydrogenation. There are nine kilocalories in each gram of fat. Fatty acids such as conjugated linoleic acid, catalpic acid, eleostearic acid and punicic acid, in addition to providing energy, represent potent immune modulatory molecules.
Enoyl-CoA hydratase
ECH catalyzes the second step (hydratation) in the breakdown of fatty acids (β-oxidation). Fatty acid metabolism is how human bodies turn fats into energy. Fats in foods are generally in the form of triglycerols. These must be broken down in order for the fats to pass into human bodies. When that happens, three fatty acids are released.
Saturated fat
Guidelines released by many medical organizations including the World Health Organization have advocated for reduction in the intake of saturated fat to promote health and reduce the risk from cardiovascular diseases. Many review articles also recommend a diet low in saturated fat and argue it will lower risks of cardiovascular diseases, diabetes, or death. However, a smaller number of other reviews have come to different conclusions.
While nutrition labels regularly combine them, the saturated fatty acids appear in different proportions among food groups. Lauric and myristic acids are most commonly found in "tropical" oils (e.g., palm kernel, coconut) and dairy products. The saturated fat in meat, eggs, cacao, and nuts is primarily the triglycerides of palmitic and stearic acids.
Fatty acid metabolism
The prostaglandins are a group of physiologically active lipid compounds having diverse hormone-like effects in animals. Prostaglandins have been found in almost every tissue in humans and other animals. They are enzymatically derived from arachidonic acid a 20-carbon polyunsaturated fatty acid. Every prostaglandin therefore contains 20 carbon atoms, including a 5-carbon ring. They are a subclass of eicosanoids and form the prostanoid class of fatty acid derivatives.
Fatty acid synthesis
Fatty acid synthesis is the creation of fatty acids from acetyl-CoA and NADPH through the action of enzymes called fatty acid synthases. This process takes place in the cytoplasm of the cell. Most of the acetyl-CoA which is converted into fatty acids is derived from carbohydrates via the glycolytic pathway. The glycolytic pathway also provides the glycerol with which three fatty acids can combine (by means of ester bonds) to form triglycerides (also known as "triacylglycerols" – to distinguish them from fatty "acids" – or simply as "fat"), the final product of the lipogenic process. When only two fatty acids combine with glycerol and the third alcohol group is phosphorylated with a group such as phosphatidylcholine, a phospholipid is formed. Phospholipids form the bulk of the lipid bilayers that make up cell membranes and surround the organelles within the cells (e.g. the cell nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus etc.)
Palmitic acid
Palmitic acid, or hexadecanoic acid in IUPAC nomenclature, is the most common saturated fatty acid found in animals, plants and microorganisms. Its chemical formula is CH(CH)COOH, and its C:D is 16:0. As its name indicates, it is a major component of the oil from the fruit of oil palms (palm oil). Palmitic acid can also be found in meats, cheeses, butter, and dairy products. Palmitates are the salts and esters of palmitic acid. The palmitate anion is the observed form of palmitic acid at physiologic pH (7.4).
Cat food
One group of fatty acids that is particularly important for gastrointestinal (GI) health is the essential fatty acid (EFA) group. All EFAs are polyunsaturated (they have more than one double bond in their fatty acid chain). EFAs are important to have in the diet in adequate amounts, especially for the cat, as since they are essential (meaning the body produces little to none so it must be included in the diet) and cats have very low activity or simply lack the digestive enzymes to generate the EFAs that are important in mediating the inflammatory response. EFAs also vary in size, have many different functions and can also be further divided into other categories, two of which are very important for GI health: the omega-6 and omega-3 fatty acids (the omega in the name denotes the position of the first double bond in a fatty acid counting from the methyl end). These fatty acids are most effective when present in adequate and appropriate balanced ratios dependent upon stage of life and production of the animal. One very important function of EFAs is the production of eicosanoids (molecules that are important in immune and inflammatory regulation). 
Eicosanoids are like hormones and act in a local fashion with short lives. 
Different EFAs have different effects on the inflammatory response. 
Omega-6 fatty acids at high levels can suppress the functions of the immune system (large part of which is located in the GIT) and promote inflammation, platelet aggregation and hypersensitive reactions like allergies. 
Omega-3 fatty acids act in the opposite direction of omega-6 fatty acids by: promoting anti-inflammation and depressing aggregation and immunosuppression. 
Ratio of omega-6 to omega-3 fatty acids can be changed using diet, optimal ratio of omega-6 to omega-3 fatty acids is considered to be within the range of 5:1 to 10:1. 
The right ratio (different for everyone as everyone is unique) helps reduce inflammation and mediate immune responses as both omega fatty acids utilize the same enzymes in their metabolic journey. 
Some sources of omega-6 fatty acids include: corn oil, sunflower oil and soybean oil. 
Some sources of omega-3 fatty acids include: cold-water fish oil, flaxseed, canola oil and soybean oil.