Essential linoleic acid

One common feature of the mediterranean dietary habit is the use of olive oil as fat source in place of animal fat typical of Northern European and USA diets. As compared to other vegetable oils, olive oil is characterized by the peculiar composition of the trygliceride fraction and by the phenolic and volatile constituents which affect the organolectic properties. Olive oil is rich in monounsaturated fat (56-84% of oleic acid), contains 3-21% of the essential linoleic acid [3], is low in tocopherols [4,5] and therefore the presence of phenols is important to mantain the anti-oxidative stability. Several articles [1,2,6] reviewed the reasons why olive oil should be preferable to other dietary fat, paying particular attention to the fatty acid composition. Oleic acid is antithrombotic compared to saturated fatty acids [7]. Monounsaturated and polyunsaturated fats reduced low density lipoproteins (LDL) levels. 

SrrfHoiver oH (thistle oil, dyer s thistle oil). Oil obtained from seeds of safflower (dyer s thistle, Cartha-mus tinctorius, Asteraceae). S. is of economic interest and has some dietetic importance on account of its high content of the essential linoleic acid (70-80%) in triglyceride form it also contains in particular palmitic acid (ca. 5%) and oleic acid (10-20%). New strains of safflower have high contents of oleic acid (>60%). -[HS151211. 151219 CAS8O01-23-8]... 

The use of the isotonic soy bean oil emulsion Intraiipid "Vit-rum" to cover about 407o of the caloric requirement T> rmits peripheral vein infusions to be used exclusively for up several weeks. Furthermore, this regimen ensures a sufficient supply of the essential linoleic acid. Linoleic acid deficiency which is inevitable unless at least 107o of the caloric needs is covered with Intralipid, leads to skin changes, alterations of cellular and other membranes, and increases the caloric requirement by about 207o (16). 

Sunflower-, rapeseed-, and coconut oils, besides fat, butter-fat and Liga margarine were used in the trial. Their fatty acid composition show considerable differences. The coconut oil contains mainly lauric acid, sunflower oil comprises the essential linoleic acid, butterfat comprehends palmitic-and oleic acid, in the Liga margarine there is the oleic acid in the highest quantity,... 

Mammals are not capable of synthesizing certain unsaturated fatty acids, which ate, nevertheless, fundamental to maintain different functions, snch as the stratum comeum and the skin s barrier function (Pons and Parra, 1995). Linoleic and linolenic fatty acids are considered essential. Linoleic acid is vital for maintaining epidermal thickness and the barrier function that impedes trans-epidermal water loss. A diet lacking in these fatty acids leads to dryness and desquamation, topical application can correct these skin conditions. Linolenic acid gives rise to the prostaglandins and leukotrienes involved in inflammatory processes, which explains why it is applied topically in treatments for sensitive skin. The combination of these two fatty acids is commonly called vitamin F and it is frequently applied topically to improve dryness and dehydration in mature skin. 

Another vitamin which may be concerned in the oxidation of fats is ascorbic acid, which according to Golumbic and Mattill (7) enhances the activity of tocopherols in preventing the oxidation of certain vegetable fats. Aqueous colloidal solutions of carotene, without tocopherol, are also protected by ascorbic acid (8). It is clear, therefore, that the vitamins mentioned, and also the essential linoleic acid, may interact in fatty mediums either as substances liable to oxidation, or as antioxidants. It seems probable that future research will reveal other instances of interaction in fatty media, and possibly will implicate other vitamins. Already Paveek and Shull (9) have shonm that biotin is inactivated by rancid fats, from which it is protected by tocopherol. While in some cases the chemical behavior of the vitamins in fats may be related to their physiological activity, in others tlieir reactions when exposed to oxidative influences may merely conform with those of the other constituents of the fat. 

The unsaturated fatty acids, linoleic [60-33-3] and linolenic [463-40-17, contain two and three double bonds and are considered beneficial components of the diet. The double bond is an essential ingredient for human nutrition when it is in the correct position on the fat molecule. Humans are unable to insert the double bond at the omega-3 and -6 position. Therefore, fatty acids containing double bonds at these positions are essential in the diet, including linoleic and linolenic acids. They are accordingly described as essential fatty acids (EFA) (23). 

The word essential as applied to naturally occuning organic substances can have two different meanings. For exanple, as used in the previous section with respect to fatty acids, essential means necessary. Linoleic acid is an essential fatty acid it must be included in the diet for animals to grow properly because they lack the ability to biosynthesize it directly. 

Some fatty acids are not synthesized by mammals and yet are necessary for normal growth and life. These essential fatty aeids include llnoleic and y-linolenic acids. These must be obtained by mammals in their diet (specifically from plant sources). Arachidonic acid, which is not found in plants, can only be synthesized by mammals from linoleic acid. At least one function of the essential fatty acids is to serve as a precursor for the synthesis of eicosanoids, such as... 

Organisms differ with respect to formation, processing, and utilization of polyunsaturated fatty acids. E. coli, for example, does not have any polyunsaturated fatty acids. Eukaryotes do synthesize a variety of polyunsaturated fatty acids, certain organisms more than others. For example, plants manufacture double bonds between the A and the methyl end of the chain, but mammals cannot. Plants readily desaturate oleic acid at the 12-position (to give linoleic acid) or at both the 12- and 15-positions (producing linolenic acid). Mammals require polyunsaturated fatty acids, but must acquire them in their diet. As such, they are referred to as essential fatty acids. On the other hand, mammals can introduce double bonds between the double bond at the 8- or 9-posi-tion and the carboxyl group. Enzyme complexes in the endoplasmic reticulum desaturate the 5-position, provided a double bond exists at the 8-position, and form a double bond at the 6-position if one already exists at the 9-position. Thus, oleate can be unsaturated at the 6,7-position to give an 18 2 d5-A ,A fatty acid. 

Linoleic and a-linolenic acids are the only fatty acids known to be essential for the complete nutrition of many species of animals, including humans, and are known as the nutritionally essential fatty acids. In most mammals, arachidonic acid can be formed from linoleic acid (Figure 23-4). Double bonds can be intro-... 

Rats fed a purified nonlipid diet containing vitamins A and D exhibit a reduced growth rate and reproductive deficiency which may be cured by the addition of linoleic, a-linolenic, and arachidonic acids to the diet. These fatty acids are found in high concentrations in vegetable oils (Table 14-2) and in small amounts in animal carcasses. These essential fatty acids are required for prostaglandin, thromboxane, leukotriene, and lipoxin formation (see below), and they also have various other functions which are less well defined. Essential fatty acids are found in the stmctural lipids of the cell, often in the 2 position of phospholipids, and are concerned with the structural integrity of the mitochondrial membrane. 

There are three groups of eicosanoids that are synthesized from C20 eicosanoic acids derived from the essential fatty acids linoleate and a-linolenate, or directly from dietary arachidonate and eicosapentaenoate (Figure 23-5). Arachidonate, usually derived from the 2 position of phospholipids in the plasma membrane by the action of phospholipase Aj (Figure 24-6)—but also from the diet—is the substrate for the synthesis of the PG2, 1X2 series (prostanoids) by the cyclooxygenase pathway, or the LT4 and LX4 series by the lipoxygenase pathway, with the two pathways competing for the arachidonate substrate (Figure 23-5). 

FARAG R s, BADEL A z M A, HEWEDi F M and EL-BAROTY G s A (1989) Antioxidant activity of some spice essential oils on linoleic acid oxidation in aqueous media, JAOCS, 66, 792-9. 

The essential fatty acids in humans are linoleic acid (C-18 2 N-6) and a-linolenic acid (C18 3 N-3). Arachidonic acid (C20 4 N-6) is also essential but can be synthesized from linoleic acid. Administration of 2% to 4% of total daily calories as linoleic acid should be adequate to prevent essential fatty acid deficiency in adults (e.g., infusion of 500 mL of 20% intravenous lipid emulsion once weekly).7 Biochemical evidence of essential fatty acid deficiency can develop in about 2 to 4 weeks in adult patients receiving lipid-free PN, and clinical manifestations generally appear after an additional... 

As mentioned earlier, both MCTs and LCTs are used in tube feeding products. Corn, soy, and safflower oils have been the mainstay sources of fat in these products, providing mainly co-6 polyunsaturated fatty acids (PUFAs). On the other hand, some newer EN products contain higher quantities of co-3 PUFAs from sources such as fish oil [i.e., docosahexenoic acid (DHA) and eicosapentenoic acid or (EPA)]. Still other formulas contain higher quantities of monounsaturated fatty acids from canola oil and high-oleic safflower or sunflower oils. The essential fatty acid (EFA) content (mainly linoleic acid) of EN... 

Essential fatty acid deficiency Deficiency of linoleic acid, linolenic acid, and/or arachidonic acid, characterized by hair loss, thinning of skin, and skin desquamation. Long-chain fatty acids include trienes (containing three double-bonds [e.g., 5,8,11-eicosatrienoic acid, or Mead acid trienoic acids) and tetraenes (containing four doublebonds [e.g., arachidonic acid]). Biochemical evidence of essential fatty acid deficiency includes a trieneitetraene ratio greater than 0.4 and low linoleic or arachidonic acid plasma concentrations. 

FIGURE 3-7 Pathways for the interconversion of brain fatty acids. Palmitic acid (16 0) is the main end product of brain fatty acid synthesis. It may then be elongated, desaturated, and/or P-oxidized to form different long chain fatty acids. The monoenes (18 1 A7, 18 1 A9, 24 1 A15) are the main unsaturated fatty acids formed de novo by A9 desaturation and chain elongation. As shown, the very long chain fatty acids are a-oxidized to form a-hydroxy and odd numbered fatty acids. The polyunsaturated fatty acids are formed mainly from exogenous dietary fatty acids, such as linoleic (18 2, n-6) and a-linoleic (18 2, n-3) acids by chain elongation and desaturation at A5 and A6, as shown. A A4 desaturase has also been proposed, but its existence has been questioned. Instead, it has been shown that unsaturation at the A4 position is effected by retroconversion i.e. A6 unsaturation in the endoplasmic reticulum, followed by one cycle of P-oxidation (-C2) in peroxisomes [11], This is illustrated in the biosynthesis of DHA (22 6, n-3) above. In severe essential fatty acid deficiency, the abnormal polyenes, such as 20 3, n-9 are also synthesized de novo to substitute for the normal polyunsaturated acids. 

Essential fatty acid deficiency is rare but can occur with prolonged lipid-free parenteral nutrition, very low fat enteral formulas, severe fat malabsorption, or severe malnutrition. The body can synthesize all fatty acids except for linoleic and linolenic acid, which should constitute approximately 2% to 4% of total calorie intake. 

Unsaturated fatty adds have one or more double bonds. Humans can synthesize only a few of the unsaturated fatty acids de novo the rest must be made from essential fatty acids in the diet transported from the intestine in chylomicrons. Two important essential fatty acids are linolenic and linoleic adds. 

Fatty acids, such as linoleic, hnolenic, and arachidonic acids, contain two or more cis carbon-carbon double bonds and are referred to as polyunsaturated fatty acids. Several of these fatty acids, including linoleic and linolenic acids, are required nutrients for humans and must be part of a healthy diet. They are termed essential fatty acids, of which there are eight. These fatty acids cannot be synthesized by human beings but are essential to human health. Therefore, they must be consumed in adequate amounts in a healthy diet, specifically in the form of ingested plant-derived foods. A diet devoid of the essential fatty acids eventually results in a fatal condition characterized by inflammation of the skin (dermatitis), failure of wounds to heal, and poor growth. The essential fatty acids serve as precursors for complex molecules termed eicosanoids, to which we return below. 

Here are the key points. First, the most abundant volatiles in tomatoes are derived from catabolism of essential fatty acids. Linoleic acid is the precursor for hexanal and linolenic acid is that for cw-3-hexenal, cH-3-hexenol, and trans-2-hexenal. All of these are important flavor elements in the tomato. A healthy diet for people requires... 

Although these are termed essential fatty acids, they are, in fact, precursors for the major polyunsaturated fatty acids that have essential roles in the body but are present only in small amounts in the diet. Linoleic acid is converted, via elongation and desaturation reactions, to dihomo-y-linolenic (20 3n-6) and then to arachidonic (20 4n-6) acid. a-Linolenic is converted to eicosapentaenoic (20 5n-3) and then docosahexae-noic (22 6n-3). The pathways for formation of these latter fatty acids, from their dietary precursors, are presented in Figures 11.11 and 11.12. Full details of one pathway are provided, as an example, in Appendix 11.4. For comparison of the two pathways, they are presented side by side in Figure 11.13. 

Mobilisation of triacylglycerol is due to the increased rate of lipolysis. Adipose tissue triacylglycerol contains some essential fatty acids (linoleic and linolenic acids) and these are mobilised along with the non-essential fatty acids. The... 

Figure 20.3 Essential fatty acids in the diet, production of physiological essential acids and their roles in the cell cycle. Essential fatty adds in the diet are mainly linoleic and a-linolenic but they are converted by desaturation and elongation reactions to the essential acids that are used in phospholipid formation and synthesis of eicosanoids. (For details of the elongation and desaturation reactions and eicosanoid formation, see Chapter 11.).

Essential fatty acids are fatty acids that have to be supplied in the diet. Without exception, these are all polyunsaturated fatty acids the C20 fatty acid arachidonic add (20 4 5,8,11,14) and the two Cis acids linoleic add (18 2 9,12) and linolenic add (18 3 9,12,15). The animal organism requires arachidonic acid to synthesize eicosanoids... 

Linoleic acid and linolenic acid cannot be made in the body and are thus essential. 

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