AuthorsRodrigo Valenzuela B.Nutrition and Dietetics School, Faculty of Medicine, college of Chile, Santiago, ChileAlfonso Valenzuela B.Lipid Center, Nutrition and Food technology Institute, college of Chile, Faculty of Medicine, college of Los Andes, Santiago, Chile
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From the Edited Volume
The ax lipid is provided to divide a big number of building materials having an extremely different physics - chemical characteristics, being its solubility in necessary non-polar solvents the usual property for your classification. Lipids room composed that carbon, hydrogen and also oxygen atoms, and also in some situations contain phosphorus, nitrogen, sulfur and other elements. In this context, fats and also oils are the key exponents that lipids existing in foods and also in nutritional procedures <1,2>, being diverse fatty acids and also cholesterol the most representative molecule due their necessary metabolic and also nutritional features <3,4>. The structural, metabolic and also nutritional importance of lipids in the body is sustained by plenty of investigations in different organic models (cellular, animals and humans). Lipids have actually been critical in the evolution of species, having actually important function in the growth, breakthrough and maintenance of organization <5,6>. A clear example of this importance is the elevated fatty mountain concentration current in nerve tissue, especially really long-chain polyunsaturated fat acids <7,8>.
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Fatty mountain are, amongst lipids, of crucial relevance in the structure and physiology the the human body because: i) forms an integral component of phospholipids in cell membranes; ii) room the primary source of energy (9 kcal /g or 37.62 kjoules/g); iii) in infants, provide much more than 50% of the daily power requirements; iv) some fatty acids space of important character and are forced for the synthesis of eicosanoids and also docosanoids (of 20 and also 22 carbon atoms, respectively), such together leukotrienes, prostaglandins, thromboxanes, prostacyclins, protectins and also resolvins), and; v) few of them might act as second messengers and regulators that gene expression <9,10>. As well as fatty acids, cholesterol is one more lipid the has vital functions in the body, amongst which are: i) together with phospholipids is vital in the development of cell membranes; ii) constitutes the skeleton because that the synthetic of steroid hormones (androgens and also estrogens); iii) indigenous its framework is obtained the framework of vitamin D, and; iv) participates in the synthesis of the bile salts and the composition of bile secretion <11>.
Lipids pat a crucial role in the development and advancement of the organism, whereby the needs of these molecules (mainly fatty acids) will readjust depending top top the age and physiological state of individuals <12>. Furthermore, lipids have critical participation both, in the prevention and/or in the development of numerous diseases, especially chronic non-communicable illness <13>, affecting the lipid requirements in humans <14>. As food components, lipids are additionally important because: i) are significant in offering organoleptic features (palatability, flavor, aroma and also texture); ii) are auto for fat dissolve vitamins, pigments or dyes and also antioxidants, and; iii) may act together emulsifying agents and/or promote the security of suspensions and emulsions <15>.
Fats and also oils, the most typical lipids in food, room triacylglyceride mixtures, i.e. Structures developed by the linking the three various or comparable fatty acids to the tri-alcohol glycerol <16>. A fat is defined as a mixture that triacylglycerides i beg your pardon is solid or pasty at room temperature (usually 20 °C). Whereas the hatchet oil coincides to a mixture of triglythrade which is fluid at room temperature. In addition to triacylglycerides, which space the main components of fats and oils (over 90%), this substances frequently contain, to a lesser extent, diacylglycerides, monoacylglycerides, phospholipids, sterols, terpenes, fat alcohols, carotenoids, fat soluble vitamins, and also many various other minor chemical frameworks <17,18>. This chapter faces the general aspects of lipids, especially those regarded the chemical framework and duty of this molecules.
2. Fatty acids
Fatty acids are hydrocarbon structures (containing carbon and also hydrogen atoms) created by 4 or much more carbons attached come an acidic sensible group referred to as carboxyl group. The chemical and also physical properties of the different fatty acids, such as their solubility in non-polar solvents and the melt point, will depend on the variety of carbon atoms of the molecule. <19>. The greater the variety of carbon atoms of the chain the higher will be melting suggest of the fatty acid. According to the chain length fatty acids room referred as short-chain fat acids, those having 4 (C4) come ten (C10) carbons; together medium-chain fatty acids those having twelve (C12) come fourteen (C14) carbons; long-chain fatty acids to those of 16 (C16) come eighteen carbons (C18); and an extremely long-chain fatty acids those having actually twenty (C20) or much more carbon atoms. Molecules having less than 4 carbon atoms (C2; acetic acid and C3; propionic acid) space not thought about fatty mountain due their high water solubility. ~ above the various other side, fat acids of high number of carbon atoms room not frequent, yet are current in far-ranging amount in the brain of vertebrates, including mammals and also human. In the human brain have been identified fatty acids as lengthy as 36 carbon atoms <20>.
The link between carbons in fat acids, exchange mail to a covalent link which may be single (saturated bond) or double (unsaturated bond). The number of unsaturated bond in the very same molecules can selection from one come six dual bonds. Thus, the an ext simple classification of the fat acids, split them in those that have actually not twin bonds, called saturated fatty acids (SAFA), and fatty mountain that have one or more twin bonds, jointly named unsaturated fatty acids. In turn, as soon as the molecule has actually one unsaturation the is classified as monounsaturated fatty mountain (MUFA) and when has two to 6 unsaturations space classified as polyunsaturated fatty acids (PUFAs) <21>. The presence of unsaturation or twin bonds in fatty acids is stood for by denoting the number of carbons the the molecule followed by one indication that the number of twin bonds, thus: C18:1 coincides to a fatty mountain of 18 carbons and also one unsaturation, it will certainly be a MUFA. C20: 4 exchange mail to a molecule having 20 carbons and also four dual bonds, gift a PUFA. Now, the is necessary to recognize the place of the unsaturations in the hydrocarbon chain both in MUFAs and PUFAs <22>.
3. Nomenclature of fat acids
According come the main chemical nomenclature established by IUPAC (International Union that Practical and Applied Chemistry) carbons of fat acids have to be numbered sequentially native the carboxylic carbon (C1) come the most extreme methylene carbon (Cn), and the position of a double bond should be suggested by the symbol delta (Δ), with each other to the variety of the carbon where twin bonds begins. Follow to this nomenclature: C18: 1, Δ9, shows that the double bond is in between carbon 9 and also 10 <23>. However, in the cabinet the metabolic utilization of fatty acids wake up by the succeeding scission of 2 carbon atoms from the C1 to the Cn (mitochondrial or peroxisomal beta oxidation). This means that as the fatty mountain is being metabolized (oxidized in beta position), the number of each carbon atom will change, creating a problem for the identification of the metabolic assets formed as the oxidation progress. Thus R. Holman, in 1958, propose a new type of notation the is now widely offered for the biochemical and also nutritional identification of fatty acids <24>. This nomenclature lists the carbon enumeration indigenous the other too much of the fatty mountain molecule. According to this notation, the C1 is the carbon farthest from the carboxyl team (called as terminal or end methylene carbon) i beg your pardon is designed together "n", "ω" or "omega". The latter notation is the most regularly used in nutrition and refers to the last letter of the Greek alphabet <25>. Thus, C18: 1 Δ9 coincidentally is C18: 1 ω-9 in the “ω” notation, however C18: 2 Δ9, Δ12, according to this nomenclature ω would be C18: 2 ω-6. What happens with fatty acids having an ext than a double bond? dual bonds room not randomly i ordered it in the fatty acid structure. Nature has been "ordained" as greatly incorporate castle in well-defined positions. Many frequently double bonds in PUFAs are separated by a methyl group (or many correctly methylene group) creating a -C=C-C-C=C- structure which is recognized as "unconjugated structure", i m sorry is the layout of double bonds in many naturally arising PUFAs <26>. However, back much less frequently, there are likewise present "conjugated structures" where twin bonds room not separated by a methylene group, creating a -C=C-C=C- structure. This specific structural disposition of double bonds, i.e conjugated structures, is now getting much interest since some fatty acids having these structures show special nutritional properties, lock are dubbed "conjugated fat acids". Many of castle are acquired from the unconjugated framework of linoleic acid (C18:2 ω-6) <27,28>.
For the application of the ”ω” nomenclature and also considering the "order" of dual bonds in unsaturated fat acids having actually unconjugated stucture, it deserve to be observed the by pointing the place of the first twin bond, it will automatically determined the ar of the subsequent dual bonds <29>. Thus, C18: 1 ω-9, which has actually a single double bond at C9 counted indigenous the methyl end, correspond to oleic mountain (OA), which is the key exponent of the ω-9 family. Oleic acid is very abundant both in vegetable and animal tissues. C18: 2 ω-6 corresponds to a fatty mountain having double bonds at the C6 and C9 (for unconjugated fat acids the is not essential to show the place of the second or successive double bonds). This is linoleic mountain (LA), the main exponent that the ω-6 family and also which is really abundant in vegetables oils and to a lesser extent in pet fats <30>. C18: 3, ω-3 synchronizes to a fatty acid having twin bonds in ~ C3, C6 and C9. It is alpha-linolenic acid (ALA), the leading exponent the the ω-3 family. ALA is a much less abundant fat acid, nearly exclusively present in the vegetable kingdom and also specifically in land-based plants <31>. Within (LCPUFAs), C20: 4, ω-6 or arachidonic mountain (AA); C20: 5, ω-3 or eicosapentaenoic acid (EPA) and; C22 : 6, ω-3 or docosahexaenoic mountain (DHA), space of good nutritional importance and are only found in ground animal tissues (AA) and in aquatic pet tissues (AA, EPA and also DHA) and in tree of naval origin (EPA and DHA) <32>.
The boost of double bonds in fat acids considerably reduces its melt point. Thus, because that a structure of the same variety of carbon atoms, if that is saturated may give rise to a solid or semisolid product in ~ room temperature, but if the very same structure is unsaturated, may originate a fluid or much less solid product at room temperature. Number 1 shows the category of fatty acids follow to their level of saturation and unsaturation and considering the notation "ω", and table 1 shows various fatty acids, reflecting the C nomenclature, their systematic name, their common name and the respective melting point.
Classification of fat acids follow to their level of saturation and unsaturation and considering the notation " ω".
|Nomenclature||Systematic name||Common name||Melting allude °C|
|Saturated fatty Acid|
|Unsaturated fat Acid|
Different fat acids, showing the C nomenclature, their methodical name, their common name and also the corresponding melting point.
4. Mono-, di- and triacylglycerides
The structural company of fat acids in food and also in the human body is mainly identified by the binding to glycerol through ester linkages. The reaction of a hydroxyl team of glycerol, at any of its 3 groups, v a fatty acid offers rise come a monoacylglyceride. The linking that a 2nd fatty acid, which might be similar or various from the existing fatty acid, gives rise come a diacylglyceride. If all 3 hydroxyl teams of glycerol are linked by fat acids, climate this will be a triacylglyceride <33>. Monoacylglycerides, through having totally free hydroxyl groups (two) are fairly polar and also therefore partly soluble in water. Different monoacylglycerides linked to fat acids of various lengths are offered as emulsifiers in the food and pharmaceutical industry <34>. The less polar diacylglycerides which have actually only one free hydroxyl group are much less polar 보다 monoacylglycerides and also less soluble in water. Finally, triacylglycerides, which absence of cost-free hydroxyl groups are completely non-polar, yet highly soluble in non-polar solvents, which are commonly used for their extraction from vegetables or pet tissues, since constitutes the energy reserve in these tissues <35>. Diacylglycerides and also monoacylglycerides are necessary intermediates in the digestive and also absorption process of fats and also oils in animals. In turn, some of these molecules also perform various other metabolic functions, such as diacylglycerides which might act together "second messengers" in ~ the intracellular level and also are also part of the ingredient of a brand-new generation of oils nutritionally designed as "low calorie oils" <36>. As soon as glycerol develops mono-, di-, or triacylglycerides, its carbon atoms are not chemically and also structurally equivalent. Thus, carbon 1 the the glycerol is referred as carbon (α), or sn-1 (from “stereochemical number”); carbon 2 is referred together carbon (β), or sn-2, and carbon 3 together (γ), or sn-3. That is important to keep in mind that the notation “sn” is right now the most frequently used <37>. This spatial structure (or conformation) the mono-, di- and also triacyglycerides is relevant in the digestive procedure of fats and also oils (ref). Figure 2 reflects the structure of a monoacylglceride, a diacylglyceride and a triacylglyceride, specifying the "sn-" notation.
Structure of a monoacylglyceride, a diacylglyceride and a triacylglyceride, specifying the "sn-" notation
5. Essential fatty acids
The capacity of an organism to metabolically introduce dual bonds in specific positions that a fatty mountain or the inability to carry out this, identify the existence of the so-called non-essential or necessary fatty acids (EFAs). According to this capability, mammals, including primates and also humans, deserve to introduce a twin bond just at the C9 position of a saturation fatty mountain (according come "ω" nomenclature) and also to various other carbons nearest to the carboxyl group, but not at carbons nearest the C1 position <38>. This is the reason why OA is not an EFA. In contrast, mammals have the right to not introduce double bonds at C6 and C3 positions, gift the factor why AL and also ALA are EFAs. By derivation, the AA is created by the elongation and desaturation of LA, and EPA and also DHA, i beg your pardon are created by elongation and desaturation of ALA, become additionally essential for mammals once their corresponding precursors (LA and also ALA, respectively) space nutritionally deficient <39>. Number 3 reflects the chemical framework of a SAFA, such as the stearic acid (C18:0), AO, LA and also ALA, exemplifying the "ω" notation the each and also indicating the essential condition in relation to the position of their unsaturated bonds.
The chemical framework of a SAFA, such as the stearic mountain (C18:0), AO, LA and also ALA, exemplifying the "ω" notation of each and also indicating the essential condition in relationship to the position of your unsaturated bonds
6. Isomerism of fat acids
According come the distribution of double bonds in a fatty acid and to that is spatial structure, unsaturated fat acids may have two species of isomerism: geometrical isomerism and also positional isomerism. By isomerism that is referred to the existence two or much more molecules having actually the same structural elements (atoms), the same chemical formula and linked in equal proportions, however having a different position or spatial distribution of some atoms in the molecule <40>.
6.1. Geometrical isomers of fat acids
Carbon atoms creating the framework of the fatty acids own a three-dimensional spatial framework which develops a perfect tetrahedron. However, once two carbons having tetrahedral structure are joined together with a twin bond, the spatial construction of the twin bond is amendment adopting a level or plane structure <41>. Rotation around solitary bonds (C-C) is entirely free, yet when they are forming a double bond (C=C), this rotation is impeded and also the hydrogen atoms that are attached to each carbon connected in the bond may be at the very same side or protest in the aircraft forming the dual bond. If hydrogen atoms remain at the same side, the structure developed is referred together cisisomer (denoted as “c”). As soon as hydrogen atoms continue to be at opposite sides the structure formed is referred as transisomer (denoted together “t”, trans: means crossed) <42>. Figure 4 reflects the cis– transgeometric isomerism of fatty acids. The cisor transisomerism of fatty acids confers them really different physical properties, gift the melting suggest one the the most relevant <43>. Table 2 mirrors the melting point of miscellaneous cis– transgeometric isomers of various fatty acids. It have the right to be observed substantial differences in the melting suggest of cis- or transisomers because that the same fatty acid. Melting point differences lug to the geometrical isomers of a fat acid very different biochemical and nutritional behavior. Fat acids having actually transisomerism, specifically those of technical origin (such as generated during the partial hydrogenation of oils), have actually adverse impact on humans, specifically referred come the risk of cardiovascular illness <44>. It is remarkable that the bulk of naturally arising fatty acids have cisisomerism, back thermodynamically is much more stable the transthan the cisisomerism, through which under details technological manipulations, such as the application of high temperature (frying process) or during the hydrogenation process applied for the manufacture of shortenings, cisisomers are conveniently transformed right into transisomers <45>.
6.2. Positional isomers of fatty acids
Positional isomerism describes the different positions that have the right to occupy one or more twin bonds in the framework of a fat acid. Because that example, oleic mountain (C18:1 Δ9c), is a usual fatty acid in vegetables oils, specifically in olive oil, but vaccenic acid (C18:1 Δ11t) is an ext common in pet fats. This is a dual example, due to the fact that both fatty acids space geometric isomers (oleic acid cisand vaccenic acid trans) and also at the exact same time positional isomers, due to the fact that oleic acid has a dual bond at the Δ9 position and also vaccenic mountain at the Δ11 place <46>.
|Fatty acid||Isomerism||Melting allude (°C)|
|C18:3||cis, cis, cis||11.0|
|C20:3||trans, trans, trans||29.5|
Changes in the melting allude of miscellaneous cis – transgeometrical isomers of different fatty acids
In general, every fatty acids naturally existing positional isomerism of their an ext frequent molecule structure. However, these isomers happen in really low concentrations. Unlike the recognized biochemical and nutritional impacts of transgeometric isomers, there is tiny information around the organic effects of positional isomers and also for the majority of castle these effects are thought about as not relevant, other than for part conjugated structures, such as conjugated linoleic mountain (C18:2, Δ9, Δ11, CLA), a geometric and positional isomer the the most common linoleic acid, for which it has been deadline various health properties, especially those regarded anti-inflammatory and lipolytic actions, but up to day the scientific proof for this properties are taken into consideration insufficient <47>. Such as geometrical isomerism, the technical manipulation of fat acids (i.e. Temperature and/or hydrogenation) boosts the number and also complexity the the positional isomers <48>. Figure 5 summarizes the positional and geometric isomers of unsaturated fat acids.
Phospholipids room minor materials in our diet since less than 4-5% of our fat intake coincides to phospholipids. However, this does no detract nutritionally important to these lipids, due to the fact that they are crucial constituents that the cellular structure having additionally relevant metabolic functions <49>. Life, in that origin, would certainly not have actually been feasible without the appearance of phospholipids, together these structures space the basic components of every cellular membranes. Phospholipids have structural and also functional properties that differentiate them from your counterparts, triacylglycerides. In phospholipids positions sn-1 and sn-2 of the glycerol moiety are lived in by fatty acids, much more frequently polyunsaturated fat acids, connected to glycerol by ester bonds. The sn-3 position of glycerol is connected to orthophosphoric mountain <50>. The structure which is formed, elevation of the type of fatty acid that binds at sn-1 and sn-2, is referred to as phosphatidic acid. The existence of phosphate substituent at the sn-3 position of the glycerol provides a good polarity to this component of the molecule, being non-polar the remainder of the structure, such together in triacylglycerides. This dual feature, a polar extreme and also a non-polar domain due the existence of the two fatty mountain characterizes phospholipids as amphipathic molecules (amphi: both; pathos: sensation) <51>.
Positional and geometric isomers of unsaturated fat acids
The structure of phospholipids is usually simplified representing the polar end as a sphere and also the fat acids as 2 parallel rods. Number 6 mirrors the chemical structure of phosphatidic mountain in its streamlined representation. The amphipathic personality of phosphatidic acid can be enhanced by joining to the phosphate different an easy and polar molecule that boosts the polarity to the extreme of the sn-3 position. Once the substituent the the phosphate team is the aminoacid serine it is formed phosphatidylserine; as soon as it is etanolamine it is formed phosphatidylethanolamine (frequently recognized as cephalin); when choline is the substituent it is developed phosphatidylcholine (well well-known as lecithin); and when the substituent is the polyalcohol inositol that is formed phosphatidylinositol, a really important molecule affiliated in cabinet signaling. <52>.
Chemical structure of phosphatidic acid and also its streamlined representation
These more facility phospholipids are much more common than phosphatidic acid, because this is just the structural precursor of the over molecules. Number 7 reflects the structure of miscellaneous phospholipids. A variety of other molecule are likewise classified as phospholipids, but are structurally different. Cardiolipin is a "double" phospholipid in which two phosphatidic acid molecules space attached through their phosphates by a molecule of glycerol. Cardiolipin is a an extremely important in the framework of the inner membrane that mitochondria and due your molecular volume the is the only immunogenic phospholipid (which stimulates the formation of antibodies) <53>. Plasmalogens are various other lipid molecules regarded phospholipids. In this molecules the substituent in ~ sn-1 place of the glycerol is not a fatty acid, yet a fat alcohol which is connected to glycerol by one ether linkage. Phosphatidalethanolamine (different than phosphatidylethanolamine) is an abundant plasmalogen in the nervous tissue <54>. Phosphatidalcholine, the plasmalogen concerned phosphatidylcholine, is abundant in the love muscle. One more structures concerned phospholipids space sphingolipids. In these frameworks glycerol is replaced by the amino alcohol; sphingosine. Once the hydroxyl team (alcoholic group) the sphingosine is substituted through phosphocholine, the is developed sphingomyelin, which is the only sphingolipid the is current in significant amount in human being tissues together a ingredient of myelin that develops nerve fibers . Platelet activating variable (PAF) is an inexplicable glycerophospholipid structure. In this molecule place sn-1 of glycerol is linked to a saturation alcohol with an ether bond (such as in plasmalogens) and also at the sn-2 binds an acetyl team instead the a fat acid. PAF is released by a variety of cells and also by binding come membrane receptor produces aggregation and degranulation the platelets, has potent thrombotic and also inflammatory effects, and is a mediator the anaphylactic reaction <55>.
Structure of miscellaneous phospholipids
A an essential aspect that phospholipids is their participation in the framework of biological membranes, and the structural features of the fat acids are appropriate to recognize the behavior and also the organic properties that the membrane. As an example, a diet affluent in saturated fat acids an outcome in rise in the levels of this fatty acids right into cell membrane phospholipids, causing a significant decrease in both, membrane fluidity and also in the capacity of these structure to incorporate ion channels, receptors, enzymes, structural proteins, etc., effect which is connected to an enhanced cardiovascular hazard <56>. By contrast, a diet rich in monounsaturated and/or polyunsaturated fatty acids develop an inverse effect. At the nutritional and metabolic level this impact is very relevant because as the fatty mountain composition of the diet is straight reflected right into the fatty acid composition of phospholipids, transforms in the ingredient of the diet, i.e. Increasing the content of polyunsaturated fat acids, will prevent the advance of several diseases <57>. Figure 8 mirrors a simulation just how the structural differences of the fat acids which comprise phospholipids may influence the physical and also chemical behavior of a membrane.
Sterols are obtained from a usual structural precursor, the sterane or cyclopentanoperhydrophenanthrene, consisting in a main structure created by four aromatic rings established as A, B, C and also D rings. Every sterols have actually at carbon 3 the A ring a polar hydroxyl group being the remainder of the structure non-polar, which offers them certain amphipathic character, such as phospholipids. Sterols have additionally a twin bound in ~ carbons 5 and also 6 that ring B <58>. This twin bond deserve to be saturated (reduced) which leader to the development of stanols, which in addition to plant sterols derivatives are right now used together hypocholesterolemic agents when incorporated into some useful foods. In ~ carbon 17 (ring D) both sterols together stanols have attached an aliphatic group, consists in a linear structure the 8, 9 or 10 carbon atoms, depending upon whether the sterol is from pet origin (8 carbon atoms) or native vegetable origin (9 or 10 carbon atoms) <59>. Figure 9 mirrors the framework of cyclopentanoperhydrophenanthrene and cholesterol. Frequently sterols, and less regular stanols, have actually esterified the hydroxyl group of carbon 3 (ring A) with a saturated fatty acid (usually palmitic; C16:0) or unsaturated fatty mountain (most frequent oleic; C18:1 and less constant linoleic acid; C18:2. The esterification that the hydroxyl team eliminates the anphipaticity that the molecule and converts it right into a structure completely non-polar. Undoubtedly among sterols cholesterol is the most important since it is the precursor the important pet metabolic molecules, such as steroid hormones, bile salts, vitamin D, and also oxysterols, which are oxidized derivatives the cholesterol created by the thermal manipulation the cholesterol and also that have actually been established as regulators of the metabolism and also homeostasis the cholesterol and sterols in basic <60>.
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Simulation how the structural distinctions of the fat acids which comprise phospholipids may affect the physical and chemical habits of a membrane
Lipids space a large and wide group the molecules that are existing in all living biology and additionally in foods and also characterized by particular physicochemical properties, such as their non polarity and their solubility in organic solvents. Part lipids, in details fatty acids and sterols, are crucial for animal and plant life. Lipids are key elements in the structure, biochemistry, physiology, and also nutritional condition of an individual, since are associated in: i) the to move structure; ii) the cellular energy reserve, iii) the formation of regulation metabolites, and; iv) in the regulation and also gene expression, which straight affects the functioning of the body. One more important facet related come lipids is their necessary involvement, either in the treatment and/or the beginning of many diseases which can impact humans. Structural and functional attributes of lipids, questioned in this chapter, will permit you to incorporate those metabolic aspects of this important and also essential molecule in close relationship of how foodstuffs containing these molecules deserve to have a relevant influence in the health or illness of one individual.