Fatty acids are monocarboxylic acids characterized by a long unbranched hydrocarbon chain (chain of carbon atoms, called aliphatic chain, with only one carboxylic group (-COOH) at one end). Fundamental components of lipids, they can also be defined aliphatic monocarboxylic acids derived or contained in esterified form in a vegetable or animal fat, in an oil or in a wax; generally fatty acids have an even number of carbon atoms, with a chain from 4 to 30 carbon atoms, even if in some foods, such as vegetable oils, we find minimum percentages with an odd number.
The aliphatic chain that constitutes them tends to be linear and only in rare cases occurs in a branched or cyclic form; the length of this chain is extremely important, as it affects the physical and chemical characteristics of the fatty acid: as it gets longer, the solubility in water decreases and, consequently, the melting point increases; since each fatty acid is formed by an aliphatic carbonaceous chain (hydrophobic) ending with a carboxylic group (hydrophilic), they are considered amphipathic or amphiphilic molecules: thanks to this chemical characteristic of theirs, when they are placed in water they tend to form micelles, spherical structures with a hydrophilic shell, constituted by the carboxylic heads, and with a lipophilic heart, constituted by the aliphatic chains, heavily conditioning the entire digestive process of lipids.
Based on the presence or absence of one or more double bonds in the aliphatic chain, fatty acids are defined as saturated (SFA, saturated fatty acids) when their chemical structure does not contain double bonds, unsaturated when one or more double bonds are present: based on the position of the hydrogen atoms associated with the carbons engaged in the double bond, a fatty acid can exist in nature in two forms, a cis, if the two hydrogen atoms bound to the carbons engaged in the double bond are arranged on the same plane, and a trans, if the spatial arrangement is opposite; the cis form lowers the melting point of the fatty acid and increases its fluidity. In nature, cis fatty acids clearly predominate over trans; the presence of cis double bonds lowers the melting point of the lipid and results in a curvature of the fatty acid that increases as the presence of double bonds increases.
Saturated fatty acids can be of natural origin or derived by hydrogenation of unsaturated fatty acids; in nature there are many forms of saturated fatty acids that differ from each other for the number of carbon atoms of the molecule, which starting from the three atoms of propionic acid come up to the hexatryoctahedral acid that has a chain of 36 carbon atoms.
In the human body fatty acids are very abundant, but rarely free and mostly esterified with glycerol (triacylglycerols, glycerophospholipids) or with cholesterol (cholesterol esters). When found in their free form (i.e., not bound to other chemical species), fatty acids are identified as free fatty acids or FFA, free fatty acids, or NEFA, nonesterified fatty acids.
Some unsaturated fatty acids are considered particularly important for the human metabolism, so they are called essential fatty acids or EFA, essential fatty acids, and are classified as omega-3, when the last double bond is present on the third carbon starting from the end, as in the case of α-linolenic acid (C 18:3 ω-3), or omega-6, when the last double bond is present on the sixth carbon starting from the end, as linoleic acid (C 18:2 ω-6).
Essential Fatty Acids
Called in the past “vitamin F” or called with the acronym EFA (Essential Fatty Acids), are a family of fatty acids that, being indispensable for the body metabolism, must be taken through the dietary intake, since they cannot be synthesized by the body itself.
Short-chain fatty acids
Short-chain fatty acids (also called SCFA), acronym that stands for “short chain fatty acids”, are saturated fatty acids with an aliphatic chain (carbon chain) composed of less than 6 carbon atoms: generally, when we talk about these substances, we refer to acetic acid (C2), propionic acid (C3) and butyric acid (C4).
Dietary intake and intestinal absorption
Hardly present in food, they are produced in the intestine by anaerobic fermentation, by the intestinal microbiota, starting from complex carbohydrates or dietary fibers such as undigested starch (resistant starch), pectin and fructo-oligosaccharides (FOS): it is estimated that the caloric contribution of these fatty acids is about 10% of the body’s energy needs.
They are absorbed by the organism at the level of the small intestine, both of the colon mucosa, and can be used as an energy source at a local level or be carried to the liver by the portal circulation: butyrate (butyric acid ester), together with glutamine, represents the major energy source for the colon, so much so that its deficiency determines mucosal atrophy; butyric acid plays, also increasing the blood flow locally, a fundamental action in ensuring sufficient energy to the cells of the wall, to prevent ulcerative phenomena and promote the repair of the intestinal mucosa.
There is a relationship between intestinal dysbiosis, with a consequent decrease in the availability of butyric acid, and the onset of irritable bowel syndrome or ulcerative colitis: the action of these short-chain fatty acids is not only expressed through the increase of vascularization or the action of energy support, but also through modulation of the immune response of the gut-associated lymphoid tissue (GALT) and an action of control and regulation of the hypothalamic-pituitary-adrenal axis (HPA axis).
In contrast to long-chain fatty acids (LCFA), SCFA are not able to form triglycerides, composed of fatty acids and glycerol, or other esterifications: Short-chain fatty acids, as well as medium-chain fatty acids (MCFA or MCT), are absorbed as such in the intestine and conveyed directly to the liver through the portal vein, being partially soluble in water, unlike long-chain fatty acids, which are incorporated in the chylomicrons and absorbed through the lymphatic capillaries present in the intestinal interstitial spaces, and through the Pecquet’s cistern and the thoracic duct, access the bloodstream via the subclavian artery.
Medium chain fatty acids
Medium-chain fatty acids (also called MCFA) are saturated fatty acids with an aliphatic chain (carbon chain) composed of 6÷12 carbon atoms: generally, when we talk about these substances, we refer to caproic acid (C6), caprylic acid (C8), caprinic acid (C10) and lauric acid (C12); even if butyric acid (C4) belongs to short chain fatty acids (SCFA), it is often considered assimilable, from a nutritional point of view, to medium chain fatty acids.
They are usually esterified with glycerol, forming the medium chain triglycerides also known as MCT: from a dietary point of view, 10/20% of sheep, goat and cow milk contains MCT and the same percentage is detectable in the butter extracted from these dairy products; other sources are palm seeds and coconut, which can make available high quantities in their oils.
Their metabolic fate is directly correlated to that of MCTs, which have peculiar dietary characteristics, as they undergo digestive processes substantially different from LCTs and LCFAs; unlike long-chain fatty acids, they are partially water-soluble and are more easily attacked by lipases present in the gastro-intestinal tract and do not require the emulsifying action of bile salts; they cross more easily the aqueous layer that bathes the intestinal villi, being, therefore, poured directly into the portal circulation, where they are conjugated to albumin and transported to the liver, without first passing through the lymphatic route.
MCT, and consequently MCFA, are able to stimulate the action of the immune system, increasing the phagocytic activity. Caprylic acid has antifungal characteristics, carrying out an effective anti-candida action and exerts a competitive action against viruses and bacteria. Lauric acid is endowed with antiseptic properties.
Long-chain fatty acids
Long-chain fatty acids (also called LCFA) are a class of fatty acids with an aliphatic chain consisting of more than 12 carbon atoms.
Very long chain fatty acids
A very long chain fatty acid (hence the acronym VLCFA) is a long chain fatty acid with an aliphatic chain consisting of more than 22 carbon atoms. In contrast to many fatty acids, long chain fatty acids are too large to be metabolized in the mitochondria and must be processed in the peroxisomes, which have their own enzymes to oxidize these molecules.
Cetylated fatty acids
Family of fatty acids used both by the cosmetic industry and as nutritional supplements in the treatment of inflammatory joint processes, often obtained through the esterification of oils or fats, even if normally present in nature: in this family of cetyl esters, the best known is cetylmiristoleate, also known by the name of cerasomal-cis-9-cetylmiristoleate or CMO, being used in the treatment of rheumatoid arthritis; other fats belonging to this group of lipophilic substances, such as cetylmyristate, cetylpalmitoleate, cetillaureate, and cetyloleate, also appear to be effective as a remedy for the symptoms of osteoarthritis and ankylosing spondylitis.
Although there are not enough clinical evidences confirming their efficacy, they are used for the treatment of autoimmune diseases such as Sjogren’s syndrome, Systemic Lupus Erythematosus and Multiple Sclerosis: some authors believe that they can also be used in fibromyalgia. The use of cetylated fatty acids can be done either orally, as often happens with cetyl myristoleate, or through topical application, as in the case of mixtures of cetyl esters, applied locally at the level of joints affected by osteoarthritis, to improve joint function and the ability to move, and reduce pain symptoms.
Some researchers hypothesize that cetyl esters are able to confer to cell membranes a greater integrity and to stabilize the lipid structure, improving its functioning and promoting its regeneration and repair in case of noxae or inflammatory processes: although acting at systemic level, it seems that cetylated fatty acids have a selective efficacy for the arthro-muscular system. The usefulness in the reduction of inflammation and pain, at the joint level, has been clinically demonstrated, in particular in the case of cetylmiristoleate: it is assumed that the mechanism of action depends on the inhibition of the genesis of chemical mediators of inflammation, similarly to what happens for polyunsaturated fatty acids (in particular of the family of PUFA Ω3).
The use seems to be able to decrease the phlogosis, increase the production of synovial fluid with consequent improvement of joint lubrication and restoration of joint integrity, reducing the deterioration of cartilage, improving flexibility and reducing joint swelling and stiffness; the best results are obtained if the assumption of CMO is associated with mixtures containing PUFA Ω3 (especially EPA and DHA of marine origin) together with soy lecithins and if it is preceded by detoxification of the body. Topical application also appears to act on muscle contractures and thickening of tendon sheaths and periarticular connective tissues.
The use of cetylated fatty acids is indicated for:
- rheumatoid arthritis: we owe to the studies of Dr. Len Sands, director of the San Diego International Immunological Center, the idea of using cetylmyristoleate for the treatment of this pathology;
- osteoarthritis: improves flexibility, mobility and reduces soreness, especially in the knee, but is not particularly effective on morning stiffness;
- ankylosing spondylitis.
According to some authors, the action on cell membranes and mediators of inflammation makes the use of these fatty acids potentially effective in inflammatory processes and autoimmune diseases such as:
- Reiter’s syndrome;
- Sjogren’s syndrome;
- Lupus Eritematosus Sistemicus;
- Behçet’s syndrome;
- Multiple Sclerosis.
Cetylated fatty acids are also used in the treatment of disorders such as:
- Pulmonary Emphysema;
- Benign Prostatic Hyperplasia.