**1.7 Cis-trans fatty acids**

The naturally occurring unsaturated fatty acids have predominantly a *cis* carbon-carbon double bond ( ). The C=C double bond typically lies on C-9 for the C18 unsaturated fatty acids. However, the artificial hydrogenation of C-18 unsaturated fatty acids such as linoleic acid (C18:2, ω-6) may produce *cis*-*trans* conjugated fatty acid (CLA), like isomers of *cis* Δ-9, *trans* Δ-11; *cis* Δ-9, *trans* Δ-12; and *trans* Δ-10, *cis* Δ-12. Hydrogenation may produce other forms of *trans* fatty acids (TFAs), such as *trans* Δ-8, *trans* Δ-9, and *trans* Δ-10 elaidic acid and *trans* Δ-11 vaccenic acid (**Figure 3**). *Trans* fatty acids (TFAs) are a kind of unsaturated fatty acids and also nonessential fatty acids. The primary TFAs are elaidic acid and vaccenic acid. The vaccenic acid is produced by bacteria in cattle rumen and thus may pass into humans via the milk of cows. The *trans* Δ-9 elaidic acid is the major industrial isomer of TFA [15].

The reports on the effect of CLAs on health and diseases are still scant. Raff et al. [16] reported that a 50:50 mixture of *cis* Δ-9, *trans* Δ-11 CLA and *trans* Δ-10, *cis* Δ-12 CLA caused a nonsignificant increase in SBP (by only 3 mmHg) without any effect on DBP in humans. Laso et al. [17] reported that CLA did not have any effect on blood pressure. Zock and Katan [18] reported that CLAs increase LDL-C and decrease HDL-C, thus indicating that CLA can act as a potential vascular risk factor. American Heart Association, the American Dietetic Association, the Institute of Medicine, US Dietary Guidelines, and the National Cholesterol

**15**

**Figure 4.**

*the fatty acid.*

*Fatty Acids: From Membrane Ingredients to Signaling Molecules*

gest that the effects of CLA remain to be resolved cautiously.

**2. Physicochemical properties of fatty acids**

Education Program Adult Treatment Panel are claiming to limit *trans* fatty acids in the daily diet [19]. We have previously reported that *cis* Δ-9, *trans* Δ*-*11-conjugated linoleic acid promotes neuronal differentiation [20] in rats. These reports thus sug-

Fatty acids are ubiquitous biological molecules. They are esterified to numerous complex lipid molecules, including triglycerides, phospholipids, and cholesterol esters. As being part of these molecules, fatty acids thus may govern some of their physical properties. The aliphatic chains and their lengths confer hydrophobicity to fatty acids. The hydrophobic nature of the fatty acids renders them insoluble in

At very high pH, where the longer chained fatty acids are totally ionized, they form micelles, which are thermodynamically stable aggregates of molecules in aqueous solution [21]. This property confers the ionized fatty acids to detergent properties. However, to achieve a stable micelle formation, the fatty acids must be present in a solution at a pH greater than 9, which is generally unphysiologic. In fact, the most probable state of fatty acids at physiological temperature and pH is a membrane-like bilayer structure [22] (**Figure 4**, the middle one). The chain length of the fatty acid is interrelated with melting point; the higher the chain length, the lower the melting point. The double bonds in the (poly)unsaturated fatty acids further decrease their melting points [23]. This is very critical to the survival of mammals that live in extremely cold environments such as the polar areas of the earth. The presence of fatty acids in the bilayer membranes provides an excellent anisotropic solution for other membrane constituents. They confer fluidity to the membrane bilayer [24], wherein membrane-bound receptors, enzymes, and other proteins can diffuse laterally along the surface of the bilayer membrane. Phospholipids can also flip-flop between the bilayer leaflets and/or fatty acyl chains can have a vertical motion (translational motion). The word membrane fluidity can thus be referred to as the degree of stiffness or rigidity of the cellular bilayers. As saturated fatty acids are straight-chained, they can pack/stack easily with themselves and/or with the neighbor-cholesterol in the bilayer membrane. The (poly)unsaturated fatty acyl chains, on the other hand, retain bent(s) along the long axis of the chain at the

position of double bonds; thus, they cannot align/stack tightly (**Figure 5**). Consequently, they increase the degree of membrane fluidity. Therefore, the greater the degree of unsaturation of the fatty acids, the higher the fluidity of the membrane. We have previously reported the DHA, which has six double bonds, contributes to a greater extent in membrane fluidity than less-unsaturated

*The arrangements of fatty acids in aqueous environments at T > Tc. T = temperature. Tc = melting point of*

*DOI: http://dx.doi.org/10.5772/intechopen.80430*

aqueous environments.

**Figure 3.**

*The structural features of the most common cis-trans unsaturated fatty acids.*

*Biochemistry and Health Benefits of Fatty Acids*

**1.7 Cis-trans fatty acids**

**Figure 2.**

industrial isomer of TFA [15].

The naturally occurring unsaturated fatty acids have predominantly a *cis* carbon-carbon double bond ( ). The C=C double bond typically lies on C-9 for the C18 unsaturated fatty acids. However, the artificial hydrogenation of C-18 unsaturated fatty acids such as linoleic acid (C18:2, ω-6) may produce *cis*-*trans* conjugated fatty acid (CLA), like isomers of *cis* Δ-9, *trans* Δ-11; *cis* Δ-9, *trans* Δ-12; and *trans* Δ-10, *cis* Δ-12. Hydrogenation may produce other forms of *trans* fatty acids (TFAs), such as *trans* Δ-8, *trans* Δ-9, and *trans* Δ-10 elaidic acid and *trans* Δ-11 vaccenic acid (**Figure 3**). *Trans* fatty acids (TFAs) are a kind of unsaturated fatty acids and also nonessential fatty acids. The primary TFAs are elaidic acid and vaccenic acid. The vaccenic acid is produced by bacteria in cattle rumen and thus may pass into humans via the milk of cows. The *trans* Δ-9 elaidic acid is the major

*The structural features of the most common ω-7 and ω-9 unsaturated fatty acids.*

The reports on the effect of CLAs on health and diseases are still scant. Raff et al. [16] reported that a 50:50 mixture of *cis* Δ-9, *trans* Δ-11 CLA and *trans* Δ-10, *cis* Δ-12 CLA caused a nonsignificant increase in SBP (by only 3 mmHg) without any effect on DBP in humans. Laso et al. [17] reported that CLA did not have any effect on blood pressure. Zock and Katan [18] reported that CLAs increase LDL-C and decrease HDL-C, thus indicating that CLA can act as a potential vascular risk factor. American Heart Association, the American Dietetic Association, the Institute of Medicine, US Dietary Guidelines, and the National Cholesterol

**14**

**Figure 3.**

*The structural features of the most common cis-trans unsaturated fatty acids.*

Education Program Adult Treatment Panel are claiming to limit *trans* fatty acids in the daily diet [19]. We have previously reported that *cis* Δ-9, *trans* Δ*-*11-conjugated linoleic acid promotes neuronal differentiation [20] in rats. These reports thus suggest that the effects of CLA remain to be resolved cautiously.
