Dietary components essential fatty acids

The dietary precursor of the eicosanoids is the essential fatty acid, linoleic acid. It is elongated and desaturated to arachidonic acid, the immediate precursor of prostaglandins, which is stored in the membrane as a component of a phospholipid—generally phosphatidyl-inositol (PI). Arachidonic acid is released from PI by phospholipase A2. 

In addition to providing energy, dietary components also produce precursors for the synthesis of structural compounds and supply the essential fatty acids and amino acids (which the body cannot synthesize) and the vitamins and minerals (which often serve as cofactors for enzymes). 

There are many unanswered questions about the dual role that ether lipids serve as membrane components and as cellular signaling molecules. Although it is clear that arachidonic acid is closely associated and tenaciously retained by ether lipids in membranes, even in essential fatty acid deficiency, much remains to be elucidated about the enzymatic systems and regulatory controls that affect the release of this sequestered pool of arachidonic acid for its subsequent conversion to bioactive eicosanoid metabolites. The significance of ether lipids as a dietary nutrient has received little attention even though they occur in a variety of foods and it is known that ether lipid supplements are readily incorporated into cellular lipids. 

Linoleic add A - Loctadecadienoic acid, CH3-(CH2)4-CH = CH-CH2-CH=CH-(CH2)r-COOH, an essential fatty acid, M, 280.44, m.p. S C, b.p., 202°C.L.a. is widely distributed in plants and animals It occurs as an esterified component in many fats and oils, and it is found in phosphatides It is an essential dietary constituent for mammals... 

In attempting to answer this question, let us first of all consider the extent of variation in the intake of essential fatty acids likely to be encountered in different countries of the world. Data compiled by the Food and Agriculture Organization of the United Nations (1971) indicate that the fat component of human diets may contribute anywhere from just over 10% to more than 40% of the total calories. The various fats and oils that go to make up this dietary fat differ widely in their content of linoleic acid, the major dietary essential fatty acid. The diunsaturated (18 2) fatty acid content of different dietary fats and oils is shown in Table 2. In some cases, this is not all linoleic acid (e.g. butter contains only about 0.8% linoleic acid), but in most cases, the diunsaturated fatty acid can be equated with linoleic acid. Animal fats generally contain less linoleic acid than plant fats, but there is considerable overlap, as seen in Table 2. 

In animals, certain unsaturated fatty acids, such as linolenic or linoleic acids, are essential dietary components. Whether these compounds can be synthesized by man has not been determined, but since they are widely present in fats ordinarily consumed, deficiency seems an unlikely possibility. In dogs, there is evidence for a need of fat above that necessary to relieve specific effects of essential fatty acid deficiency (Chapter 7). This may be true in other species, including man. 

Dietary n-6 PUFAs include the fatty acids, LA (C18 2n-6), y-linolenic acid (C18 3n-6), dihomo-y-linolenic acid (C20 3n-6), arachidonic acid (AA C20 4n-6), adrenic acid (C22 4n-6) and docosapentaenoic acid (C22 5n-6 National Academy of Sciences et al., 2005). LA is an essential fatty acid because humans cannot synthesize it. Without dietary LA, deficiency occurs, producing adverse clinical symptoms, including reduced growth and a scaly rash (National Academy of Sciences et al., 2005). In the body, n-6 PUFAs function as a component of structural cell... 

The last essential dietary components to which we will refer and which were also discovered through feeding experiments with rats, are certain unsaturated fatty acids identified as linoleic, linolenic, and arachidonic acids by Burr and Burr in 1930. The acids are required for the formation of complex lipids which are essential in membranes for the maintenance of their fluidity (Chapter 9). Deficiencies lead to a dermatitis which does not respond to additional B vitamin supplements or to oleic acid. 

The fatty acids are a family of long-chain carboxylic acids that may be saturated, monounsaturated, or polyunsaturated. Several fatty acids are essential components of the human diet. Dietary intake of fats has important implications for health and well-being. 

The fatty acid content of our diet has important consequences for health. Several fatty acid are essential dietary components. In general, saturated and trans fatty acids are inimical to good health. In contrast, omega-3 fatty acids are favorable to good health. 

The n-6 and n-3 families are two principal families of polyunsaturated fatty acids occurring in nature and derived biosynthetically from linoleic (9-cis, 12-cw-octadecadienoic or C18 2n-6) and a-linoleific (9-cis, 12-ds, 15-c/5-octadecatrienoic or C18 3n-3) acids, respectively (Fig. 6). Both fatty acids are synthesized in plants that can insert double bonds at the A9, A12, and A15 positions in a C18 chain but not in aifimals (they can insert double bonds at the A9, but not at A12 and A15). Therefore, these two acids are essential dietary components. In aifimals, additional double bonds are inserted between the carboxyl group and the A9 position by A 5 and A 6 desaturase enzymes, and the chain can also be extended in two carbon units at the carboxyl end of the molecules by elongase enzymes. 

It is well established that fatty acids are an essential component of human nutrition (Burr and Burr, 1929) besides being the densest dietary energy source, they have important structural roles in the human body. Fatty acids that cannot be synthesised by humans are considered essential and must be provided by the intake of food (Miles and Calder, 1998). 

The first proof that fats comprise a necessary component in the diet was adduced in 1926 by Evans and Burr. Shortly thereafter, McAmis et al. (1929) also reported that rats grew better on fat-containing diets than on regimens deficient in this foodstuff in fact, the latter workers reported deficiency symptoms in rats which received the fat-free diets. It remained for Burr and Burr (1929) to demonstrate in a clear-cut manner that the beneficial effect of fat on growth was due to the fact that it prevented a dietary disease. This deficiency condition was not to be ascribed to the lack of vitamins A and D, but rather to the absence of components present in the saponifiable fraction. The latter active compounds were shown to be polyunsaturated fatty acids, which are usually referred to as essential fatty adds (EFA). The fat eficiency symptoms produced by a fat-free diet were found to disappear in a dramatic fashion when certain unsaturated fats, or linoleic, linolenic, or arachidonic acids, were fed (Burr and Burr, 1930). Earlier reviews of the nutritional significance of the EFA included that of Burr (1942), and of... 

---