Polyunsaturated Fatty Acids Omega6 Fatty Acids

evidence that certain SFAs raise blood cholesterol levels whereas PUFAs lower them was a justification for several major diet trials designed to lower CHD risk by feeding a high-fat diet (about 40% of calories) that was low in SFA and very high in PUFA (16 to 20% of calories; Oslo Diet Heart Study, 19; VA Diet Heart Study, 20; Finnish Mental Hospital Study, 21). These studies all showed that this diet lowered CHD risk by 24 to 53% concomitant with a reduction in serum cholesterol of 13 to 15%. Because of the perception that these diets might be associated with a higher incidence of cancer and also because this diet is not consumed by population groups worldwide to meaningfully assess its safety, it has not widely been recommended for the prevention and treatment of CHD.

Recent studies have reported that while PUFA has a greater total and LDL cholesterol-lowering effect versus MUFA, the differences are not as great as once believed. Thus, for practical purposes, MUFA or PUFA will elicit effects that are quite similar when incorporated in a diet that meets current recommendations for total fat (£30% of calories) and PUFA (<10% of calories). Some experts advocate, however, that PUFA not exceed approximately 7% of total energy (22). Collectively, the results of many studies indicate that while high levels of dietary PUFA seem to beneficially affect CHD, within the range of recommended intake, PUFA and MUFA have effects on plasma lipids and lipoproteins that are quite similar. Thus, either can be incorporated into the diet resulting in comparable effects.

Although some of the early studies suggested that high intakes of PUFA were associated with an increased risk of certain cancers, a recent meta-analysis of the literature concluded that a high intake of PUFA did not increase the risk of various cancers (23). This analysis did not rule out the possibility of a small increase in risk, however.

Omega-3 Fatty Acids. The early 1970s marked the beginning of a new era of investigation into the role of omega-3 fatty acids in the development of CVD. The seminal studies of Dyerberg et al. (24) showed that serum cholesterol and ^-lipoprotein levels were lower in Greenland Eskimos compared with Danish subjects who consumed a high SFA diet. Interestingly, coronary atherosclerotic disease was rare in the Eskimos and prevalent in the Danes. These scientists attributed this difference in the incidence of CHD to the high intake of marine oils and in particular, two predominant constituent highly unsaturated fatty acids, eicosapentaenoic acid (EPA, C20:5) and docosahexaenoic acid (DHA, C22:6). During the past 30 years numerous studies have demonstrated that these fatty acids have diverse biological effects. Collectively, they confer impressive cardioprotective effects via multiple mechanisms that involve antiarrhythmic actions, sudden death, thrombosis, growth of atherosclerotic plaques, lipids, and lipoproteins.

Restenosis is the disproportionate activation of one or several normal wound-healing responses that occur as the result of coronary artery bypass surgery or other invasive procedures. The clinical significance of this is that while angioplasty may initially increase lumen size by 20 to 40% and restore blood flow, a significant number of individuals (approximately 30 to 40%) undergoing the procedure will experience restenosis leading to luminal narrowing within 3 to 6 months, which requires another intervention procedure. Meta-analyses established that overall, restenosis was reduced by 14 to 29% by supplemental fish oils (25). Interestingly, when angiography was used to define coronary restenosis, there was a direct relationship between dose of omega-3 fatty acids and the reduction in restenosis. A recent large clinical trial, however, failed to find a beneficial effect of fish oil on restenosis after coronary angioplasty (26).

Impressive evidence indicates that omega-3 fatty acids reduce sudden death (27,28). In the initial report of the Lyon Diet Heart Trial (27), patients who had suffered a myocardial infarction (MI) followed an American Heart Association (AHA) Step 1 "Mediterranean-type" diet rich in linolenic acid versus a prudent Western-type diet. There was a striking reduction in coronary events and, in particular, no sudden deaths in the treatment group (versus 8 in the control group) despite no improvement in lipids, lipoproteins, and body mass index (BMI). These results have been corroborated in a population-based case-control study (28). In this study, as little as one fatty fish meal per week (ie, 1.4 g of omega-3 fatty acids per week) decreased the risk of primary cardiac arrest by 50%. More recently, the final report from the Lyon Diet Heart Trial (29) found that a Mediterranean dietary pattern (high in linolenic acid) reduced all cardiac death and nonfatal MI by approximately 70% and all coronary events measured by about 50%.

Fatty fish consumption has been shown to prevent cardiac arrest from ventricular fibrillation (28). In addition, omega-3 fatty acids have been shown to favorably affect susceptibility to premature ventricular contractions (30). These data are significant because they suggest that fish intake affects risk of CHD via events that are distinct from the effects of fish consumption on plasma lipids.

There is convincing evidence that a major beneficial effect of omega-3 fatty acids is on the prevention of thrombosis (31). Omega-3 fatty acids reduce platelet aggregation (including reactivity and adhesion) and vasoconstriction. In addition, omega-3 fatty acids favorably affect hemosta-sis. These effects are the result of enhanced fibrinolysis and reduced blood clot formation.

Fish oil has a marked hypotriglyceridemic effect in both normotriglyceridemic and hypertriglyceridemic ( >2 mmol/ L) individuals. The addition of approximately 9 to 13 g/day of fish oil (eg, 1.1 to 7 g/day of omega-3 fatty acids) resulted in a plasma triglyceride decrease of about 20 to 25% in normotriglyceridemic individuals and a decrease of about 26 to 33% in hypertriglyceridemic individuals. These levels of fish oil have a modest LDL cholesterol-raising effect (eg, 4 to 5%) in normotriglyceridemic individuals. In comparison, LDL cholesterol is elevated approximately 5 to 11% in hypertriglyceridemic individuals, and even more so (30%) in some individuals with familial hyperlipidemia (Type IV/V) (32). Thus, fish oil supplements can be an effective treatment for some patients with hypertriglyceridemia, although close monitoring by a physician is essential to ensure that there is not a concurrent significant increase in LDL cholesterol.

Conjugated Linoleic Acid. Conjugated linoleic acid (CLA) is a collective term given to a group of linoleic acid isomers in which the double bonds are conjugated instead of being in the typical methylene interrupted configuration. CLA levels are higher in animal products than in plant products and, in general, CLA levels are higher in ruminant than nonruminant tissues. CLA has attracted great interest recently because of the evidence that it favorably affects several major chronic diseases, most notably cancer, obesity/overweight, and CVD. The evidence about the biological effects of CLA to date has originated from cell culture and experimental animal studies. Providing 0.1 to 1% CLA in the diet has been reported to suppress tumor incidence in models using carcinogens that require or do not require metabolic activation, suggesting that more than one metabolic mechanism may account for the anticarcinogenic properties of CLAs. At least one study has shown that CLA supplementation to normal human mammary cells or to MCF-7 human mammary tumor cells did not lead to increased intracellular lipid peroxidation, whereas linoleic acid did (33). Thus, it is possible that the effect of CLA relates to differences in the ability to enhance free radical formation.

With respect to CVD there is limited but interesting evidence that CLA may beneficially affect plasma lipids and lipoproteins as well as atherosclerosis in rabbits (34) and hamsters (35). In both studies, the CLA treatment groups had markedly lower («20%) total and LDL cholesterol levels and triglyceride levels. HDL cholesterol levels were unaffected by CLA. Based on the study of Nicolosi et al. (35), CLA had more potent effects than linoleic acid. Collectively, these studies are highly suggestive that CLA may have a more potent cardioprotective effect beyond that of the predominant fatty acids in the diet. In addition, while CLA has antioxidant effects, little is known about whether CLA protects against oxidative modification of LDL.

100 Weight Loss Tips

100 Weight Loss Tips

Make a plan If you want to lose weight, you need to make a plan for it. Planning involves setting your goals both short term and long term ones. With proper planning, you would be able to have an effective guide on the steps that you want to take, towards losing pounds of weight. Aside from that, it would also keep you motivated.

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