Trans Fatty Acids and CHD

Early investigations into a link between dietary tram fatty acid (TFA) intake and plasma cholesterol level in clinical trials, and CHD in epidemiology studies provided conflicting results. This outcome resulted from small numbers of participants in the trials combined with poor experimental 

In the early 1990s, a series of well-designed clinical studies convincingly demonstrated that TFAs increased plasma total and LDL-cholesterol to levels similar to those produced by saturated fatty acids. More than this, TFAs reduced plasma HDL-cholesterol level. The overall effect was that the ratio of LDL-cholesterol to HDL-cholesterol was approximately double that for an equivalent intake of saturated fatty acids (Ascherio et al., 1999). In addition, TFAs adversely affect other CHD risk factors. Plasma triglycerides and Lp[a] levels are increased (Ascherio et al., 1999) and it was shown recently that consumption of TFAs was associated with a deleterious increase in small, dense LDL particles (Mauger et al., 2003). 

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A number of epidemiological studies have suggested an association between trans fatty acids and CHD. 

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-... 

The influence of trans fatty acids on plasma lipoproteins in relation to CHD risk would thus appear to be more unfavorable than that of saturated fatty acids, as determined by the effect on the ratio of LDL to FIDL cholesterol. However, the overall magnitude of the effect would be dependent on the relative intakes of trans fatty acids and saturated fatty acids. In the UK trans fatty acids contribute about 2% of dietary energy, in contrast to saturated fatty acids which contribute about 15% dietary energy, and this needs to be considered when formulating dietary advice. The Task Force also estimated, on the same basis, that a reduction of 6% in energy from saturated fatty acids would decrease risk by 37%. 

Trans fatty acids Trans fatty acids (Figure 27.13) are chemically classified as unsaturated fatty acids, but behave more like saturated fatty acids in the body, that is, they elevate serum LDL (but not HDL), and they increase the risk of CHD. Trans fatty acids do not occur naturally in plants and only occur in small amounts in animals. However, trans fatty acids are formed during the hydrogenation of liquid vegetable oils, for example, in the manufacture of margarine. 

Fatty acids affect CHD risk, in part, via effects on plasma lipids and lipoproteins. A meta-analysis of 60 controlled trials (Mensink et al., 2003) reported that saturated and trans fatty acids increase low-density lipoprotein cholesterol (LDL-C), whereas unsaturated fatty acids decrease LDL-C. Saturated fatty acids, MUFA, and PUFA all increase high-density lipoprotein cholesterol (HDL-C), whereas trans fatty acids do not. Both MUFA and PUFA decrease the TC to HDL-C ratio, whereas trans fatty acids increase it, and SFA have little effect (Fig. 20.4). 

The 1995 BNF Task Force calculated that, in the UK, replacing 2% energy from trans fatty acids with 2% energy from oleic acid would reduce mean plasma LDL cholesterol concentration by 0.08 mmol 1 plasma FIDL concentration would rise by 0.026 mmol 1 , and the FIDL ratio would fall from 3.92 to 3.77. From estimates of the effect of changes in LDL and FIDL concentrations on CHD risk, this was predicted to reduce the risk of CHD by 5-15%. In comparison, replacing trans fatty acids with either saturated fatty acids or carbohydrate would decrease risk by up to 8%. 

The relationship between trans fatty acid intake and subsequent CHD events was investigated in approximately 85 000 US nurses (the Nurses Health Study). Trans fatty acid intake was calculated from food frequency questionnaires for women who had been diagnosed free from CHD, stroke, diabetes, and hypercholesterolemia. The... 

The details of population dietary guidelines for the quality and quantity of fat intake differ between countries. However, in consideration of prevention of CHD, dietary guidelines generally reflect advice to reduce average total fat intakes to 30-35% dietary energy and to lower saturated fat intakes to approximately 10% of dietary energy. Though the effect of trans fatty acids on the plasma LDL/ HDL ratio is less favorable than that of saturated fatty acids, dietary advice needs to reflect the relative intakes of these two types of fatty acids. Since... 

The consumption of foods high in TFA has been shown to raise low-density lipoprotein cholesterol (LDL or bad cholesterol), which increases the risk of developing coronary heart disease (CHD). This prompted the Food and Drug Administration (FDA) to require mandatory labeling of the fran -fat content in foods. Food manufacturers have to comply by January 1, 2006. The FDA s chemical definition of TFA or trans-fats (TF) is unsaturated fatty acids that contain one or more isolated (i.e., nonconjugated) double bonds in the frani-configuration. ... 

The relationship of dietary saturated fat to plasma cholesterol levels and to CHD was graphically demonstrated by the Seven Countries Study involving 16 cohorts, in which saturated fat intake explained up to 73% of the total variance in CHD across these cohorts. In the Nurses Health Study, the effect of saturated fatty acids was much more modest, especially if saturates were replaced by carbohydrates. The most effective replacement for saturated fatty acids in terms of CHD prevention is by polyunsaturated fatty acids (PUFAs). This agrees with the outcome of large randomized clinical trials, in which replacement of saturated and trans fats by polyunsaturated vegetable oils effectively lowered CHD risk. 

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