Saturated fat

Saturated fat is fat that consists of triglycerides containing only saturated fatty acids.

Explanation

Fat that occurs naturally in living matter contains varying proportions of saturated and unsaturated fat. Examples of foods containing a high proportion of saturated fat include dairy products (especially cream and cheese but also butter and ghee), animal fats such as suet, tallow, lard and fatty meat, coconut oil, cottonseed oil, palm kernel oil, chocolate, and some prepared foods^[1].

There are several kinds of naturally occurring saturated fatty acids, their only difference being the number of carbon atoms - from 1 to 24. Saturated fatty acids have no double bonds between the carbon atoms of the fatty acid chain; hence, they are fully saturated with hydrogen atoms.

While nutrition labels usually lump them together, the saturated fatty acids appear in different proportions among food groups. Lauric and myristic acids are most commonly found in "tropical" oils (e.g. palm kernel, coconut) and dairy products. The saturated fat in meat, eggs, chocolate and nuts is primarily palmitic and stearic acid.

Examples of saturated fatty acids

Some common examples of fatty acids are:

• lauric acid with 12 carbon atoms (contained in coconut oil, palm oil and breast milk,
• 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),
• stearic acid with 18 carbon atoms (also contained in meat and cocoa butter).

Harvard Nurses' Health Study found that diets lower in carbohydrate and higher in protein and animal fat are associated with a statistically insignificant decrease in risk of coronary heart disease in women. When vegetable sources of fat and protein are chosen, these diets may moderately reduce the risk of coronary heart disease." ^[3]

Diets high in saturated fat are correlated with an increased incidence of atherosclerosis and coronary heart disease according to a number of studies, both in African green monkeys^[4] and humans, such as a study of infant diets ^[5], 22 hypercholesterolemic men ^[6][7][8] Some 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.^{[9][10][11][12]} Additionally, controlled experimental studies have found that people consuming high saturated fat diets experience negative cholesterol profile changes.^{[5][13][14][15]} 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.^[16]

Experiments in which subjects were randomly assigned to either a control or Mediterranean diet (which replaces saturated fat with mono and polyunsaturated fat) showed that subjects assigned to a Mediterranean diet exhibited a significantly decreased likelihood of suffering a second heart attack, cardiac death, heart failure or stroke.^[17][18]

Epidemiological studies of heart disease have implicated the four major saturated fatty acids to varying degrees. The World Health Organization has determined that there is "convincing" evidence that myristic and palmitic acid intake increases the probability, "possible" risk from lauric acid, and no increased risk at all from stearic acid consumption.^[19]

In a study published in 2001, erythrocyte membrane oleic and monounsaturated fatty acid content was positively associated with breast cancer risk in postmenopausal women, while no association was shown between saturated fatty acids and breast cancer risk. Enzyme Δ9-desaturase catalyzes the conversion of stearic acid to oleic acid: there is a negative correlation between erythrocyte membrane oleic acid and dietary polyunsaturated fatty acids. Inverse relationship between Saturation Index (ratio of membrane stearic to oleic acid) and breast cancer risk could also be related to hormonal and metabolic factors and to interactions between them, as well as to dietary factors.^[20]

Dietary recommendations

A 2004 statement released by the Centers for Disease Control (CDC) determined that "Americans need to continue working to reduce saturated fat intake..." ^[21] 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.^{[22] [23]} This concurs with similar conclusions made by the World Health Organization (WHO) and the US Department of Health and Human Services, both of which determined that reduction in saturated fat consumption would positively affect health and reduce the prevalence of heart disease.^{[24][16] [25]}

The World Health Organization (WHO) 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. ^{[26] [27]}

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-(saturated)fat foods may be in part due to the high content in glycotoxins, above and beyond those due to oxidized fatty acid derivatives." [34] The glycotoxins, as he called them, are more commonly called AGEs^[28]

Contrary research

See also: Lipid hypothesis

• A 3-year study of 235 postmenopausal women conducted by Mozaffarian et al was released in 2004. The study subjects all had established coronary artery disease. Most were hypertensive and many had diabetes (19–31%). Their body mass index ranged from 29 to 30 and their lipid profile indicated combined hyperlipidemia. These combined characteristics are consistent with metabolic syndrome. 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 study concluded that "in postmenopausal women with relatively low total fat intake, a greater saturated fat intake is associated with less progression of coronary atherosclerosis." 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".^[29][30][31]

• A study of 297 acute MI cases in Portuguese males, published in February 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". The researchers 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".^[32]

• Fulani of northern Nigeria get around 25% of energy from saturated fat, yet their lipid profile is indicative of a low risk of cardiovascular disease. This finding is likely due to their high activity level and their low total energy intake.^[33]

• A 2004 article in The American Journal of Clinical Nutrition raised the possibility that the supposed causal relationship between saturated fats and heart disease may actually be a statistical mistake because of the greater precision with which saturated fats have been measured.^[34]

Molecular description

Two-dimensional representation of the saturated fatty acid myristic acid.

A space-filling model of the saturated fatty acid myristic acid.

See also

References