Trans Fatty acids metabolism

Oxidation of Trans Fats Unsaturated fats with trans double bonds are commonly referred to as trans fats. There has been much discussion about the effects of dietary trans fats on health. In their investigations of the effects of trans fatty acid metabolism on health, Yu and colleagues (2004) showed that a model trans fatty acid was processed differently from its cis isomer. They used three related 18-carbon fatty acids to explore the difference in /3 oxidation between cis and trans isomers of the same-size fatty acid. 

This finding has been replicated several times in clinical studies. Let me cite one example. In a careful metabolic study carried out in 1990, Mensink and Katan determined the plasma LDL/HDL ratio when 10% of the energy from oleic acid was replaced in the diet by either the corresponding trans fat or the corresponding saturated fatty acid, stearic acid. The resulting LDL/HDL ratios were 2.02 on the oleic acid diet, 2.34 on the stearic acid diet, and 2.58 on the trans fatty acid diet. This is one more example of the impact of small structural changes in molecules on their biological properties. 

Figure 22.6 How various factors increase the risk of atherosclerosis, thrombosis and myocardial infarction. The diagram provides suggestions as to how various factors increase the risk of development of the trio of cardiovascular problems. The factors include an excessive intake of total fat, which increases activity of clotting factors, especially factor VIII an excessive intake of saturated or trans fatty acids that change the structure of the plasma membrane of cells, such as endothelial cells, which increases the risk of platelet aggregation or susceptibility of the membrane to injury excessive intake of salt - which increases blood pressure, as does smoking and low physical activity a high intake of fat or cholesterol or a low intake of antioxidants, vitamin 6 2 and folic acid, which can lead either to direct chemical damage (e.g. oxidation) to the structure of LDL or an increase in the serum level of LDL, which also increases the risk of chemical damage to LDL. A low intake of folate and vitamin B12 also decreases metabolism of homocysteine, so that the plasma concentration increases, which can damage the endothelial membrane due to formation of thiolactone.

When trans-fatty acids are fed to rats with adequate amounts of essential fatty acids, they have little effect on growth, longevity, or reproduction, but when fed as the sole source of lipids they exaggerate the symptoms of essential fatty acid deficiency (111). An effect on the metabolism of long chain polyunsaturated fatty acids was noted however. 

Catalytic hydrogenation of vegetable oils is widely used to form harder fats and to decrease the content of polyunsaturated fatty acyl groups. The products have a greatly increased resistance to rancidity. However, they also contain fats with trans double bonds as well as isomers with double bonds in unusual positions.251 253 Such compounds may interfere with normal fatty acid metabolism and also appear to affect serum lipoprotein levels adversely. Trans fatty acids are present in some foods. One hundred grams of butter contain 4-8 g, but hydrogenated fats often contain much more. It has been estimated that in the United States trans fatty acids account for 6-8% of total dietary fat.253... 

Bauman, D.E., Lock A.L., Corl B.A., IpC., Salter A.M., Parodi P.W. 2005. Milk fatty acids and human health potential role of conjugated linoleic acid and trans fatty acids. In Ruminant Physiology Digestion, Metabolism and Impact of Nutrition on Gene Expression, Immunology and Stress. (K. Sejrsen, T. Hvelplund, and M.O. Nielsen, eds.), pp. 523-555, Wageningen Academic Publishers, Wageningen, The Netherlands. Academic Publishers. 

A process with potential practical applicability is the hydrogenation of edible oils. Reduction of multiply unsaturated triglycerides with hydrogen over Ni-based catalysts is frequently used to gain autoxidative stability of edible oils. According to the Polanyi-Horiuti mechanism, multiple 1,2 or 1,4 diadsorption of the fatty acid tail with exclusively c/s-configuration around the double bonds causes cis-trans isomerisation, whilst the number of double bonds is being reduced. The trans-fatty acid chains have adverse effects on the human metabolism and must be minimized. 

The reaction catalyzed by delta-6-desaturase enzyme is the slowest reaction in the metabolic pathway of LA and is considered as a rate-limiting step (4, 5). Activity of this enzyme further decreases with age and in people suffering from various diseases, including arthritis, diabetes, hypertension, eczema, psoriasis, and so on. Lifestyle factors like stress, smoking, excessive consumption of alcohol, linoleic acid (6), saturated and trans-fatty acids and nutritional deficiencies of Vitamin B6, zinc (7), and magnesium inhibit this desaturase. As a result of limitations in in vivo production of GLA, supplementation with preformed GLA is becoming important. This has led to interest in development and commercialization of the sources of GLA. 

Latruffe, N., M. Cherkaoui-Malki, V. Nicolas-Frances, B. Jannin, M.-C. Clemencet, F. Hansmannel, P. Passilly-Degrace and J.-P. Berlot. Peroxisome-proliferator-activated receptors as physiological sensors of fatty acid metabolism molecular regulation in peroxisomes. Biochem. Soc. Trans. 29 305-309, 2001. 

The adverse effects of trans fatty acids on serum lipids and lipoproteins are thought to be mediated by alterations in lipid catabolism and metabolism. Trans fatty acids increase the catabolism rates of apolipoprotein A-I and decrease apolipoprotein B catabolism rates (Matthan et al., 2004), reduce LDL-C particle size (Mauger et al., 2003), and can increase cholesteryl ester transfer protein (CETP) activity (van Tol et al., 1995). CETP mediates the transfer of cholesterol esters from HDL- to LDL- and very-low-density lipoprotein (VLDL)-C, thereby offering a potential explanation for the LDL-C-raising and HDL-C-lowering effect of trans fatty acids. 

Evidenee suggests that the type of fat in plant-based diets is more important than the amoimt of fat in determining risk of CHD. Hu et al. foimd a significant positive assoeiation between intake of trans fatty acids and risk of CHD and an invCTse association between polyimsatnrated fat and CHD." Data from several otha- prospective studies also showed a strong inverse relation between intake of polyunsaturated fats and Metabolic stndies have shown strong cholesterol-lowCT-... 

Emken, E.A. (1995) Trans Fatty Acids and Coronary Heart Disease Risk Physiochemical Properties, Intake and Metabolism, Am. J. CUtl Nutr. 62, 659S-669S. 

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