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Summary of an article: DOI
 * Impact of trans fatty acids of ruminant origin compared with those from partially hydrogenated vegetable oils on CHD risk** by Maria Pfeuffer and Jürgen Schrezenmeir

Abstract
 * Similar trans fatty acids (TFAs) are present in both partially hydrogenated vegetable oils and fats from ruminant mammals; however they differ in the quantity of TFAs. While TFAs have been shown to influence low-density lipoprotein (LDL) levels and consequently pose an increased risk for coronary heart disease, no evidence suggests those TFAs present in fats from ruminant origins have the same influence on either LDL or risk of coronary heart disease.

1. Introduction
 * Partially hydrogenated oils (PHOs) and ruminant fats are the primary sources of TFAs in human diet and, despite the presence of ruminant TFAs in human diet for millennia, excessive TFA consumption poses a threat to human health. Ruminant fat sources of TFAs include beef and dairy lipids whose TFA content is typically low whereas PHO TFA content can vary greatly.
 * Recent TFA legislation has brought ruminant TFAs under investigation in order to determine whether all TFAs are alike.

2. Pattern of TFAs
 * Previous studies have shown the types and relative frequencies of TFAs present in both TFA sources. The most common TFA in ruminant fat was vaccenic acid and in PHOs was elaidic acid; both are trans-18:1 isomers.

3. Analysis of TFAs
 * There is no standard procedure to analyze a variety of foods that can differentiate TFAs from either ruminant origins or PHOs; however, some indirect methods exist to predict the proportion from a given source.

4. Metabolic properties of TFAs with relevance for human health 4.1 Lipids and Lipoproteins 4.2 Comparison of Vaccenic and Elaidic Acid Isomers in vitro 4.3 Butterfat versus PHVO in Intervention Studies 4.4 VA-enriched Butterfat 4.5 Observations from Epidemiological Studies 4.6 Rumenic Acid, cis9,trans11-CLA
 * Not only do TFAs adversely affect lipid levels, but they do so “in a more negative way than saturated fatty acids.” Lipoproteins, triglycerides, and lipids are strongly linked with or are otherwise good predictors of coronary heart disease (CHD).
 * The direct effect on plasma lipid levels is only part of the influence for increased risk of CHD, atherosclerosis also plays a role by adversely altering metabolic processes and is induced by increased inflammation. TFAs have been shown to produce a sufficient degree of inflammation to the extent that atherosclerosis plays a major role in increased risk of CHD. Certain sources of partially hydrogenated vegetable oil (PHVO) TFAs can also induce oxidative stress which poses even further health problems.
 * Evidence shows that position of the double bond can influence rate of metabolism and ultimately is related to the impact the fatty acid has in the cell. Despite its accelerated metabolism compared to elaidic acid, vaccenic acid (ruminant origin) is shown to be less incorporated into phospholipids than elaidic acid (PHVO origin). Elaidic acid among other PHVOs are also responsible for increasing total and very low-density lipoprotein triglyceride levels.
 * The lipid influences of butter as a source of saturated fatty acids, when compared with other fats, is typically overlooked and its only beneficial effect on plasma lipid levels is an increase in high-density lipoprotein cholesterol.
 * Diets composed of 20% (w/w) test fat of 3 sources (butter, VA/RA-enriched, and PHVO) were fed to a hamster cohort. Lipid profiles were compared amongst the three diets and showed that while the VA/RA-enriched and PHVO diets increased HDL cholesterol, PHVO diets increased proatherogenic lipoprotein levels including VLDL, IDL, and LDL more than VA/RA-enriched diets. VA/RA-enriched diets had the healthiest LDL/HDL ratio of the 3 diets.
 * In 1993, the first study to report TFAs from PHVOs increased coronary heart disease (CHD) was published. Since then further studies have shown that animal or dairy TFAs have either had the opposite trend or no change in risk of CHD relative to PHVO TFAs..
 * A noticeable trend of increased risk of CHD with increasing industrially modified (PHO) TFAs presents itself as a decreased risk of CHD with increased ruminant TFAs shows little opposition save for two studies whose approaches are called into question.
 * Epidemiological studies suggest that not only are TFA intake correlation with CHD risk higher than would be predicted solely on the basis of their effect on lipid levels, but also that the inflammatory levels are also underestimated at higher levels of TFA intake.
 * Ruminant origin trans fatty acid vaccenic acid (t11,18:1) is converted to cis9,trans11-conjugated linoleic acid (CLA,18:2, also known as rumenic acid, RA) in humans and showed “anti-inflammatory, antiatherosclerotic, and anticarcinogenic properties.” Rumenic acid has also shown to improve the LDL/HDL cholesterol ratio when compared to other conjugated trans fatty CLAs further categorizing the different effects various trans fats (especially those of different origins) can have on lipid and lipoprotein profiles.

5. Conclusions
 * It is uncertain which components of industrial TFAs possess that increase risk of CHD among other adverse metabolic effects discussed previously. It has been observed however that different TFA isomers possess differing physiological effects and no evidence has been shown to propose that TFAs of ruminant origin have similar negative health effect. Lastly, it should be noted that CHD risk is affected by several other environmental and dietary variables, especially involving the quality of other dietary fats, with respect to study subjects.

Pfeuffer, M.; & Schrezenmeir, J. (2006). “Impact of trans fatty acids of ruminant origin compared with those from partially hydrogenated vegetable oils on CHD risk” //International Dairy Journal, 16//(11): 1383-1388. DOI
 * Reference**