Linoleic acid dietary sources

Dietary intake is of great importance. Linoleic acid (C18 2o)6) and a-linolenic acid (C18 3o)3) are the parent essential fatty acids for humans. Both fatty acids derive from vegetable oils. Higher fatty acids are then produced by chain elongation and desaturation. In addition, some of the prime essential fatty acids, AA (C20 4o)6), EPA (C20 5w3) and DHA (C22 6w3), can be obtained directly from the diet. Meat and eggs are rich in AA, whereas fish is a rich source of EPA and DHA [14]. 

Another important dietary source of trans fat is conjugated linoleic acid, a class of compounds collectively known as CLA. Many CLA isomers contain conjugated cis/trans and trans/trans double bonds. Interest in CLA research has increased significantly in the past few years because several cis/trans CLA isomers have been reported to exhibit different beneficial physiological effects in animal studies (Yurawecz et al., 1999). The reader is referred to a collection of analytical papers published in a dossier (Mossoba, 2001, and references therein) that details several chromatographic and spectroscopic techniques and procedures that have been successfully applied to CLA analysis. 

Arachidonic acid (5,8,11,14-eicosatetraenoic acid), a polyunsaturated fatty acid derived from dietary sources or by desaturation and chain elongation of the essential fatty acid linoleic acid, is found widely in the body. It is transported in a protein-bound state and stored in the phospholipids of cell membranes in all tissues of the body [108] from where it can be changed into biologically... 

Jerusalem artichoke tubers contain little or no starch, virtually no fat, and have a relatively low calorific value. Of the small amount of fat present, trace amounts of monounsaturated and polyunsaturated fatty acids have been reported, but no saturated fatty acids (Whitney and Rolfes, 1999). The polyunsaturated fatty acids linoleic (18 2 cis, cis n-6) and a-linoleic acid (18 3 n-3) have been recorded as present at 24 mg and 36 mg-100 g 1 of raw tuber, respectively (Fineli, 2004). The tubers are a good source of dietary fiber, because of the presence of inulin. 

CLA refers to a mixture of positional and geometric isomers of linoleic acid (cis-9, cis-12 octadecadienoic acid) with a conjugated double bond system. The structure of two CLA isomers is contrasted with linoleic and vaccenic acids in Figure 3.1. The presence of CLA isomers in ruminant fat is related to the biohydrogenation of polyunsaturated fatty acids (PUFAs) in the rumen. Ruminant fats are relatively more saturated than most plant oils and this is also a consequence of biohydrogenation of dietary PUFAs by rumen bacteria. Increases in saturated fatty acids are considered undesirable, but consumption of CLA has been shown to be associated with many health benefits, and food products derived from ruminants are the major dietary source of CLA for humans. The interest in health benefits of CLA has its genesis in the research by Pariza and associates who first demonstrated that... 

Chouinard, P.Y., Corneau, L., Butler, W.R., Chilliard, Y., Drackley, J.K., Bauman, D.E. 2001. Effect of dietary lipid source on conjugated linoleic acid concentrations in milk fat. J. Dairy Sci. 84, 680-690. 

Kelly, M.L., Berry, J.R., Dwyer, D.A., Griinari, J.M., Chouinard, P.Y., Van Amburgh, M.E., Bauman, D.E. 1998a. Dietary fatty acid sources affect conjugated linoleic acid concentrations in milk from lactating dairy cows. J. Nutr. 128, 881-885. 

Chin, S. E, Liu, W., Storkson, J. M., Ha, Y. L., and Pariza, M. W. 1992. Dietary sources of conjugated dienoic fatty acids of linoleic acid, a newly recognized class of anticarcinogens. J. Food Comp. Anal., 5,185-197. 

Given the current widespread interest in reducing cancer, obesity, and other maladies, there is considerable interest in the use of the CLAs, either as a mixture or in the form of individual isomers, as beneficial dietary adjuncts. Cow s milk, beef tallow, and products made from them are natural sources of CLA. However, CLA is also readily synthesized in high yield in the laboratory from vegetable oils that are rich in linoleic acid, such as sunflower and safflower. The resulting synthetic product has CLA levels of about 80%, not the 0.3-0.5% (fat basis) found in beef tallow and dairy products (176). As a result, except for studies of the specific effects of foods containing CLA, vegetable oil is the typical source of CLA in contemporary studies and in commercial dietary supplements. This trend will probably continue. 

Linoleic acid and linolenic acid are essential fatty acids that cannot be made by animals and must be obtained by dietary intake from plant sources. When metabolized in animals, these two acids each give rise to a family of Cig, C20, and C22 n-6 and n-3 polyunsaturated fatty acids thus ... 

Archeological evidence shows that pahn oil has been consumed by humans for more than 5000 years (145). Its digestion and absorption rates in the human body are in excess of 97%, which is very similar to other common edible oils and fats. In many communities pahn oil is an important source of dietary energy and provides sufficient quantities of the essential fatty acid, linoleic acid (18 2, n-6) for normal healthy metabolic functions. Like all other edible oils of vegetable origin, palm oil is considered cholesterol free. 

The cold-pressed blueberry seed oil investigated by Parry and Yu. (3) demonstrated a high concentration of n-3 fatty acids. Alpha linolenic acid was the sole source of the n-3 and comprised 25.1 % of the total fatty acids (Table 1). The ratio of n-6 to n-3 fatty acids was 1.7 1. Linoleic acid (18 2n-6) was the most prevalent fatty acid in the blueberry seed oil followed by a-linolenic, oleic, palmitic (16 0), and stearic (18 0) acids (Table 1). The blueberry seed oil also showed a significantly higher antioxidant capacity compared with marionberry, black raspberry, cranberry, and pumpkin seed oils using the oxygen radical absorbance capacity (ORAC) test. Therefore, blueberry seed oil may serve as an excellent dietary source of n-3 fatty acids and natural antioxidants. 

The seeds of selected Onagraceae, including Oenothera picensis, O. indecora, Ludwigia longifolia, and O. L. peruviana were analyzed for their physicochemical characteristics (40). Linoleic acid was the predominant fatty acid in all tested seed oils, comprising 71.5-80.0% of the total fatty acids (Table 6) (40). These Onagraceae seed oils may be excellent dietary sources of the essential n-6 fatty acid (18 2n-6). 

Dates Phoenix dactylifera L.) are popular in most Middle Eastern countries and serve as a major source of food and nutrients (51, 52). Oil contents and fatty acid profiles of date seeds may vary among individual varieties. Date seeds contained 20-24% total fat (49). Oleic acid was the primary fatty acid in the date seed oil and had a concentration of 43.5 5% of total fatty acids. This was followed by lauric (12 0), myristic (14 0), palmitic (16 0), linoleic (18 2n6), capric (10 0), and stearic (18 0) acids along with trace amounts of other fatty acids (Table 7). Date seed oil may serve as an excellent dietary source of oleic acid with a minor amount of linoleic acid. 

Figs are a convenient single-food source broad in nutrient content, having exceptional amounts of insoluble and prebiotic dietary fiber, essential dietary minerals, and an unsaturated omega-6 fat, linoleic acid. Essential vitamins A (from carotenoids), B, and K are also present in high densities in the fig. These vitamins have an array of uses in the body—from antioxidant and metabolic roles to participation in blood coagulation and vascular function—that together support cardiovascular health. 

Today, the oil is used medicinally to treat a myriad of conditions related to essential fatty acid (EFA) deficiencies, low dietary intake of linoleic acid, and a variety of reproductive, cardiovascular, inflammatory, and neurological disorders. It is added to foods as a source of essential fatty acids and used in topical products such as soaps and cosmetics (5-7). 

Fig. 13.12 Polyunsaturated fatty acids required for eicosanoid synthesis. Oleic acid is the only fatty acid synthesized by mammals de novo. Linoleic (co-3) and a-linolenic acid (9 or greater fatty acids. Ingested o>3 fatty acids are metabolized to other co-3 fatty acids with o>9 double bonds. The same applies to co-6 fatty acids. The major dietary sources of polyunsaturated fatty acids are fish and plants oils...

The precursors of both n-6 and n-3 polyunsaturated fatty acids (PUFAs), linoleic acid and (/.-linolenic acid, respectively, are essential for mammals as they are required for normal physiological function and cannot be synthesized de novo (Holman, 1968). They can only be accumulated by placental transfer or by dietary intake. Once accretion of these fatty acids has occurred, metabolic, conservation and recycling pathways sustain them (B azan et al., 1994). Unlike mammals, plants can synthesize these precursor PUFAs (linoleic and a-linolenic acids) so they are found in abundance in the chloroplast membranes of plants, in certain vegetable oils, and in the tissues of plant-eating animals (Nettleton, 1991). The best sources of a-linolenic acid are vegetable oils, such as perilla (Yoshida et al., 1993) rapeseed (canola), linseed, walnut, and soybean (Nettleton, 1991). They are also abundant in shellfish, fish, and fish products and can be found in low amounts in green, leafy vegetables and baked beans (Nettleton, 1991 Sinclair, 1993). 

In the 1950s and 1960s, worldwide studies concluded that linoleate-rich dietary oils, such as corn oil and cottonseed oil, lowered the cholesterol level of human plasma, and therefore were advocated as preferred sources of polyunsaturated fatty acids. Hence, in the food industry, polyunsaturated began to mean two double bonds per molecule. More than two double bonds per molecule was associated with rapid unwanted rancidity. In the effort to minimize plasma cholesterol, food oils for humans became richer in linoleic acid (18 2o)6) and lower in linolenic acid (18 3o)3), but were also becoming deficient in essential (o3 polyunsaturates normally found in high levels in brain and nerve lipids. 

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