Trans-fatty acid serum cholesterol

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.

Trans-Isomers and Coronary Heart Disease An increased risk of developing heart disease has been linked to an intake of trans-fatty acids (223). The replacement of dietary saturated fatty acids by trans-fatty acids, for example, lowers serum HDL cholesterol and impairs endothelial function in healthy men and women (224). It also impairs flow-mediated vasodilation and decreases the activity of serum paraoxonase, which is an HDL-bound esterase that may protect against atherosclerosis (225). 

A note on health aspects is appropriate because the lauric oils are more than 80% saturated. This is much more than the major liquid oils such as soyabean, sunflower and rapeseed, which are respectively only 16%, 12% and 7% saturated. Nutritionally this may be thought of as a great disadvantage but such simple comparisons can be misleading. Lauric oils are only used in foods where a sharp melting hard fat is needed. When liquid oils are hydrogenated to a similar consistency, they contain not only more saturates but also trans fatty acids, which some recent studies have shown to be even more objectionable with regard to serum cholesterol profiles than the saturated ones (Byers 1997, Pietinen et al. 1998). 

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. 

Recent studies have shown that consuming a significant amount of trans fatty acids can lead to serious health problems related to serum cholesterol levels. Low overall serum cholesterol and a decreased ratio of low-density lipoprotein (LDL) cholesterol to high-density lipoprotein (HDL) cholesterol are associated with good overall cardiovascular health. High semm cholesterol and an elevated ratio of LDL cholesterol to HDL cholesterol are linked to a high incidence of cardiovascular disease, especially atherosclerosis. Research has indicated that diets high in either saturated fatty adds or trans fatty adds raise the ratio of serum LDL cholesterol to HDL cholesterol and substantially increase the risk of cardiovascular disease. 

Cis and trans isomers of dietary fats and oils are suspected to play a role in human health. All unprocessed fats and oils contain only cis isomers. During processing, some of the cis isomers are converted to trans isomers, called trans fatty acids. Trans fatty acids are suspected of raising the amount of serum cholesterol in the blood stream, which can cause health problems. 

The intermediate m hydrogenation formed by reaction of the unsaturated ester with the hydrogenated surface of the metal catalyst not only can proceed to the saturated fatty acid ester but also can dissociate to the original ester having a cis double bond or to its trans stereoisomer Unlike polyunsaturated vegetable oils which tend to reduce serum cholesterol levels the trans fats produced by partial hydrogenation have cholesterol raising effects similar to those of saturated fats... 

There is strong evidence that the risk of coronary heart disease is directly related to the plasma concentration of LDL-cholesterol and inversely related to that of HDL-cholesterol, and that the risk is reduced significantly by lowering elevated serum cholesterol levels. It has been known for many years that one of the most important dietary factors regulating serum cholesterol levels is the ratio of polyunsaturated fatty acids (PUFA) to saturated fatty acids (SFA). The SFA increase and the PUFA decrease cholesterol levels, except for the trans PUFA, which have a similar effect to the SFA. A ratio of 0.5. 9 SFA PUFA is considered to be satisfactory. It is... 

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