Dietary PUFAs

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... 

Brady, L.M., Williams, C.M., Lovegrove, J.A. 2004. Dietary PUFA and the metabolic syndrome in Indian Asians living in the UK. Proc. Nutr. Soc. 63, 115-125. 

To advance understanding of the dynamic influence of dietary lipids, research efforts are focusing on the importance of the balance between n-6 and n-3 fatty acids in the human diet. What is emerging is recognition that these PUFAs modulate eicosanoid biosynthesis in numerous tissues and cell types, alter signal transduction, and influence gene expression (87, 118). The effect of n-6 and n-3 PUFA on CVD, cancer and bone/joint health is related to the newer discoveries of how dietary PUFA impact health. 

Dietary PUFA Source Plasma Lipid Parameter Baseline (mmol/L) % Change from Baseline ... 

Dietary PUFAs decrease the plasma LDL-cholesterol level. Vegetable oils contain high levels of PUFAs such as linoleic acid (18 2), which constitutes about 25, 50, 63, and 75% of the fatty acids in peanut, soy, sunflower, and safflower oils, respectively. The quantity of 18 2 in beef and pork fat is only 5-10% and is under 3% in tropical oils. PUFAs produce decreases in LDL-cholesterol, possibly by the same (unknown) mechanism as monounsaturates. The question of whether dietary PUFAs have a greater or similar effect on LDL-cholesterol remains rmsettled. 

The long-term influence of omega-3 fatty acid supplements is not known, and, for this reason, the American Heart Association has not recommended that supplements be taken (Krauss et al., 19%). There is a very real concern that dietary PUFAs of all types may enhance the accumulation of lipid oxidation products in lipoprotein particles, thus allowing the attack of lipid oxidation products on the protein component of the LDL, the enhanced uptake of the damaged LDL by macrophages in the artery wall, and increased atherosclerosis (Allard et al., 1997 Felton et al., 1994). (Monoimsaturated fatty acids are thought not to be involved in the oxidation scenario leading to atherosclerosis.)... 

Liimatta M, Towle HC, Clarke SD, Jump DB. Dietary PUFA interfere with the insulin glucose activation of L-Type pyruvate kinase. Mol Endocrinol 1994 8 1147-1153. 

PPARa and SREBP-lc Transcriptional Sensors of Dietary PUFAs... 

Dietary PUFAs (n-6 and n-3) have been shown to confer various health benefits. In particular, the effect of PUFAs on dyslipidemia and insulin signalling is well established. PUFAs might prevent the accumulation of lipotoxic triglycerides in insulin-sensitive tissues and improve insulin sensitivity. 

PPARot was the first transcription factor identified as a fatty acid sensitive transcription factor (Gottlicher et ah, 1992). Several studies using PPARa-deficient mice provided evidence that the receptor is required for the effect of dietary PUFAs on gene expression to occur. Some of these effects arise while animals have been fed with very moderate PUFAs intake (Martin et ah, 2007). PPARot is required in vivo for the up-regulation of AOX (Ren et ah, 1997) and other enzymes involved in fatty acid transport and catabolism in the liver of mice fed with PUFAs (Martin et ah, 2007). 

Dietary Regulation of Desaturases by Dietary PUFAs in Liver... 

Further, sea lettuces show an interesting polyunsaturated fatty acid (PUFA) composition (Table 5.2). There are two major families of dietary PUFA, the (o)6) and (a)3) families. The co6 PUFA are derived from the parent compound linoleic acid [LA 18 2((b6)]. They contain at least two double bonds where the first double bond is located at sixth carbons from the methyl end of the molecule (Whelan and McEntee, 2004). Meanwhile, the co3 PUFA has the first double bond at the third carbon from the methyl... 

Stanton et al. (22) demonstrated that it is possible to modulate the milk CLA content by manipulating the cow s dietary PUFA intake. Recently, Bauman et al. (23) developed a CLA-enriched butter containing 8 times more CLA (4 vs. 0.5%) and 4 times more vaccenic acid (17 vs. 4%) than the control. In one study, rats were fed this CLA-enriched butter during the development period of the pubescent mammary gland and then switched to a control diet after administration of a carcinogen (either dimethylbenz[a] anthracene or A-methyl-A-nitrosourea). This treatment yielded a 50% reduction in mammary tumors (24). 

The traditional p/s ratio and now the n-6/n-3 PUFA ratio may be of little value because they fail to recognize the multiple effects of dietary PUFA and their metabolic interrelationships. In a multivariate system, attempts to describe a ratio of two variables have little meaning and are an inappropriate description of a mixture of fatty acids having a multiplicity of biosynthetic effects. These values should therefore be considered only as possible targets. It should be no longer valid to base dietary recommendations on the attainment of plasma... 

Vaccenic acid is an intermediate of the bacterial biohydrogenation process of dietary PUFA that is absorbed and found in tissues of dairy cows and beef cattle. 

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