Saturated fat
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Saturated fat is fat that consists of triglycerides containing only saturated fatty acids. Saturated fatty acids have no double bonds between the carbon atoms of the fatty acid chain; hence, they are fully saturated with hydrogen atoms. There are several kinds of naturally occurring saturated fatty acids, their only difference being the number of carbon atoms - from 1 to 24. Some common examples of saturated fatty acids are butyric acid with 4 carbon atoms (contained in butter), lauric acid with 12 carbon atoms (contained in breast milk, coconut oil, palm oil), myristic acid with 14 carbon atoms (contained in cow milk and dairy products), palmitic acid with 16 carbon atoms (contained in palm oil, hence the name, and meat), and stearic acid with 18 carbon atoms (also contained in meat and cocoa butter).
Fat that occurs naturally in living matter such as animals and plants is used as food for human consumption and contains varying proportions of saturated and unsaturated fat. Foods that contain a high proportion of saturated fat are butter, ghee, suet, tallow, lard, coconut oil, cottonseed oil, and palm kernel oil, dairy products (especially cream and cheese), meat, and some prepared foods[1].
The higher saturated fats such as coconut oil and cow butter are more solid at room temperature, are more stable during cooking, and have longer shelf lives than oils such as olive oil or other liquid vegetable oils. Hydrogenation of liquid vegetable oils increases their shelf life and makes them solid at room temperature. In this they are similar but not comparable to pure, unadulterated, saturated fat. Conversely, dehydrogenation converts saturated fats to unsaturated fats.
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[edit] Health issues
The relationship between dietary fats and CVD, especially coronary heart disease, has been extensively investigated, with strong and consistent associations emerging from a wide body of evidence accrued from animal experiments, as well as observational studies, clinical trials and metabolic studies conducted in diverse human populations...Saturated fatty acids raise total and low-density lipoprotein (LDL) cholesterol...The most effective replacement for saturated fatty acids in terms of coronary heart disease outcome are polyunsaturated fatty acids, especially linoleic acid. This finding is supported by the results of several large randomized clinical trials, in which replacement of saturated and trans fatty acids by polyunsaturated vegetable oils lowered coronary heart disease risk.
– World Health Organization, Population nutrient intake goals for preventing diet-related chronic diseases,5.4.4
Diets high in saturated fat are correlated with an increased incidence of atherosclerosis and coronary heart disease according to a number of studies, both African green monkeys[2] and human [3] [4][5] [6]. Numerous studies have suggested that diets high in saturated fat increase the risk of heart disease and stroke. Epidemiological studies have found that those whose diets are high in saturated fatty acids, including lauric, myristic, palmitic, and stearic acid, had a higher prevalence of coronary heart disease. [7] [8] [9] [10] Additionally, controlled experimental studies have found that people consuming high saturated fat diets experience negative cholesterol profile changes. [3] [11] [12] [13] A 2003 meta-analysis published in the American Journal of Clinical Nutrition concluded that diets high in saturated fat negatively affected cholesterol profiles – predictors of a heart attack and other cardiovascular diseases.[14]
Experiments in which subjects were randomly assigned to either a control or Mediterranean diet (which replaces saturated fat with mono and polyunsaturated fat) showed a significantly decreased likelihood of suffering a second heart attack, cardiac death, heart failure or stroke. [15] [16]
Epidemiological studies have determined that lauric acid consumption is a predictor for heart disease, though perhaps has a smaller impact than other forms of saturated fat, such as myristic and palmitic acids.[17] The World Health Organization has identified foods rich in lauric acid as a "possible" contributor to coronary heart disease.[18]
[edit] Dietary recommendations
A 2004 statement released by the CDC determined that "Americans need to continue working to reduce saturated fat intake..." [19] Additionally, reviews by the American Heart Association led the Association to recommend reducing saturated fat intake to less than 7% of total calories according to its 2006 recommendations.[20] [21] This concurs with similar conclusions made by the World Health Organization and the FDA, both of which determined that reduction in saturated fat consumption would positively affect health and reduce the prevalence of heart disease.[22][14]
The World Health Organization has concluded that saturated fats negatively affect cholesterol profiles, predisposing individuals to heart disease, and recommends avoiding saturated fats in order to reduce the risk of a cardiovascular disease. [23] [24]
[edit] Controversy
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Various studies have found that women who had regularly consumed the greatest amounts of saturated fats had the least amount of additional atherosclerotic plaque buildup in their arteries. Also, women who ate more saturated fat had a healthier balance of HDL and LDL cholesterol, and more desirable blood serum concentrations of triglycerides and free fatty acids. [25]
According to Dr. Mary Enig, a biochemist and nutritionist on fats, the many studies of saturated fat in the diet do not distinguish between saturated fat and trans fat[citation needed]. In addition, the fat found in all foods is a mixture of saturated, monounsaturated (olive oil), and polyunsaturated (canola oil, corn oil, soybean oil).
Dr. Enig also states that saturated fats are needed for the production of hormones, the stabilization of cellular membranes, the padding around organs, and for energy. Biochemical signalling processes involving G-protein, and other, receptors make extensive use of the lauric, myristic and palmitic fatty acids, since the receptors must be "coupled with lipids in order to provide localization of function". The palmitoylation and myristoylation processes make use of the palmitic and myristic fatty acids, respectively, for the purposes of stabilization. Myristic acid has been linked to proper immune system function and tumor suppression. A deficiency in the consumption of these, and other, saturated fatty acids can lead to "age-related declines in white blood cell function", along with dysfunction of the immune system, and even cancer. On the basis of extensive research conducted during the 1970s by Canadian scientists on rapeseed and canola oil, it was ultimately determined that at least 25% of fat in the diet should be in the form of saturated fat.[26]
A 3-year study of 235 women, released in 2004, concluded that "in postmenopausal women with relatively low total fat intake, a greater saturated fat intake is associated with less progression of coronary atherosclerosis.". Coronary angiography was employed to examine 2,243 coronary artery segments; once at the start of the study and once more at its conclusion. The same study revealed similarly surprising results when it was disclosed that a greater consumption of polyunsaturated oils "was also associated with greater progression of atherosclerosis".[27] [28]
A study of 297 acute MI cases in Portuguese males, published in February of 2007, concluded that, "Total fat intake, lauric acid, palmitic acid, and oleic acid were inversely associated with acute MI" and that, "Low intake of total fat and lauric acid from dairy products was related to acute MI". Nutrition Action also stated, in revealing the results of this study, that "some prospective studies show that replacing saturated fat with unsaturated fat is more effective in lowering CHD risk than reducing total fat consumption".[29]
Saturated fats have been reported to have nutritional benefits, according to Dr. Enig. Lauric acid, a medium chain fatty acid, "has antimicrobial properties and is the precursor to monolaurin, the antimicrobial lipid".[30] She also notes that lauric acid "gives human milk its major antimicrobial properties, and it may be a conditionally essential fatty acid since it cannot be made by mammals other than the lactating female and must be obtained from the diet."[31]
The initial, and most primary, scientific evidence underlying the health concerns regarding the consumption of saturated fats, is the lipid hypothesis, which argues that saturated fats cause heart disease.
There is also another issue of concern about the history behind saturated fat and trans fat. Partially and fully hydrogenated oils were actually portrayed as much healthier than the naturally occurring saturated fats. Some, such as Dr. Enig, have claimed that "big business" and other powerful vested interests played a significant role in the negative portrayals of saturated fats. [32]
Another confounding issue may be the formation of exogenous (outside the body) advanced glycation endproducts (AGEs) and oxidation products generated during cooking, which it appears some of the studies have not controlled for. It has been suggested that, "given the prominence of this type of food in the human diet, the deleterious effects of high-fat foods may be in part due to the high content in glycotoxins, above and beyond those due to oxidized fatty acid derivatives." [33] The glycotoxins, as he called them, are more commonly called AGEs.