Evidence supports a role for trans fatty acids in the development of disease. In particular, synthetic 18 carbon trans fats found in products containing hydrogenated vegetable oil are thought to cause an increased risk of cardiovascular disease. Intakes of synthetic trans fats are known to have deleterious effects on lipoprotein metabolism, and evidence suggest that high intakes of hydrogenated vegetable oils increases systemic inflammation, perhaps as a result of the trans fats they contain. This inflammation may impair endothelial function through the generation of free radicals that interfere with nitric oxide synthesis and subsequently cause endothelial dysfunction. This explains the increased risk of cardiovascular disease in those who consume trans fats. Estimates indicate a 23 % increase in ischaemic heart disease with every 2 % increase in trans fatty acids, as a percentage of total energy intake. Recommendations to minimise and even eliminate trans fatty acid have been made, thanks to the hard work of trans fat researchers like Mary Enig.
Since the start of the century, food manufacturers have become aware of a growing concerns about trans fatty acids amongst the public. As a result of their own concern for their profits, most United states manufacturers of products containing hydrogenated vegetable oil have sought to reduce or eliminate trans fatty acids in order to avoid mandatory labelling of the trans fatty acid content. Because trans fatty acid accumulate in tissues, trends in their intakes can be measured over time by sampling of tissues such as plasma, erythrocyte membranes, human milk and adipose tissue. There is therefore good reason to suspect that since the turn of the century, trans fat concentrations in humans tissues may have declined. To these ends, researchers have assessed the 18 carbon trans fat concentrations of various tissues in 305 individuals taking part in another study who had their plasma fatty acid levels measured in 20021. The researchers then assessed their fatty acid profiles in 2004 to identify changes in the concentrations of trans fats.
The results of the study showed that plasma trans fatty acids decreased by 13.5 % per year in a longitudinal trend since the original 2002 baseline measurement. These results are therefore consistent with food manufacturers attempting to remove hydrogenated vegetable oils from the diet since the beginning of the century, in order to prevent the declaration of trans fatty acids on food labels. However, while in July 2003, the American Food and Drug Administration made food manufacturers list all trans fatty acids on the labels of their products under US law, no such law exists in the United Kingdom. Only voluntary agreement between the Food Standards Agency and the food manufacturers exists, and although some manufacturers have claimed to have removed trans fats from their products, there is no guarantee that this is the case in the United Kingdom. Further, although the researchers measured the trans fatty acid profiles of the subjects over a two year period, there is no indication from this data as to the levels of trans fats in the diet since 2004.
Of course a great way to eliminate harmful synthetic trans fats from the diet is to avoid the low quality processed junk foods that contain them. This avoids the need to rely on the government to protect health. There is no known safe levels for the ingestion of synthetic 18 carbon trans fats from hydrogenated vegetable oil. However, such fats appear to have physiologically different effects that some of the natural trans fats found in dairy. In particular trans-palmitoleic acid (POA, t-C18:1 (n-7)), a natural trans fatty acid found in whole fat dairy foods may decrease rates of de novo lipogenesis and thus protect from metabolic syndrome and type 2 diabetes. It is true that trans-palmitoleic acid is also found in hydrogenated vegetable oils. However, hydrogenated vegetable oil also contains other trans fats such as elaidic acid (EA, t-C18:1 (n-9)), a trans isomer of oleic acid. The detrimental health consequences of elaidic acid likely far outweigh any beneficial effects from trans-palmitoleic acid in hydrogenated vegetable fat.
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