You may have heard of the word trans fats. You may even be aware that they are increasingly being seen as bad for the health. However, few are aware of the insidious and subtle ways that they can alter metabolism and cause disease. Trans fats occur naturally in certain unprocessed foods. Ruminants for example produce a limited amount of trans fats that are present in their milk and meat. However, the trans fats in ruminant products may not be damaging to the health because they are present in such low amounts in the diets and because the trans fats isolated from ruminants may not interfere with metabolic regulation. Ruminant products were the only sources of trans fats in the human diet for millennia, and therefore until recently humans have not been exposed to high concentrations of these fats in their foods. It was only recently with the introduction of the hydrogenation process that the trans fat content of the diet increased considerably. So what is hydrogenation and how does it produce trans fatty acids?
All vegetable oil is liquid at room temperature, and this is because it is made up of polyunsaturated fatty acids. These fats have many double bonds in their structures that provides a kink to their carbon chains. This kink occurs because chemically the fatty acids have natural a cis-configuration. This means that the hydrogen molecules around the double bonds are on the same side of the molecule, and this causes them to repel each other because they contain positive charges. This repulsion bends the molecule at the double bonds causing a kinked structure. The cis-configuration prevents the molecules being packaged closely together and therefore raises the melting and boiling points, making the fat liquid at room temperature (an oil). Vegetable oils are cheap compared to the saturated fats derived from animals, but are not useful in making spreads because they are not solid at room temperature, unlike saturated fats (which have no kink and so can pack closely together forming a solid at room temperature).
The food manufacturers therefore devised a way to turn the cheap vegetable oils into solids at room temperature. This allowed them to substitute expensive saturated fats with cheaper vegetable fats in certain products. This was achieved through hydrogenation of the vegetable oils, a process that involves passing hydrogen gas through the oil in the presence of a catalyst in order to add hydrogen molecules to the carbon chain. The result of this process is a polyunsaturated fatty acid that becomes ‘saturated’ with hydrogen, thus forming a saturated fat. Fully hydrogenated fats are chemically no different to saturated fats and this allows the use of ‘healthy vegetable oils’ in products that would normally require a saturated fat. This little nomenclature trick is used extensively in the food industry and is a confidence trick. Products using hydrogenated fats possess nothing of their vegetable origin and really this practice of using the term ‘vegetable oil’ should be made illegal where hydrogenation in present.
However, this is not the only problem with hydrogenation. Another problem arises because during the process not all of the molecules of polyunsaturated fat become fully hydrogenated. Some of the molecule are only partially hydrogenated. These fatty acids lose their cis-configuration and instead take on a trans-configuration, whereby the hydrogens that were on the same side of the molecule become moved to opposite sides. Because the hydrogens are no longer in close proximity, the natural repulsion they possess disappears and the molecule becomes straight like a saturated fat, but still retains its double bond. Such partial hydrogenation produces structural isomers of the original polyunsaturated fatty acids in the vegetable oil that act as metabolic poisons in humans. When ingested the trans fats are incorporated into metabolic pathways that are normally used by their cis-configuration counterparts, but instead of producing a useful product, they simply inhibit flux through the pathway.
Let us take for example, the essential fatty acids linoleic acid (LA, C18:2 (n-6)) and alpha linolenic acid (ALA, C18:3 (n-3)). These two fatty acids are essential to human health, and they feed into a series of metabolic pathways that produce a number of short-lived hormones called eicosanoids and docosanoids. These hormones regulate cellular functions including immunity, inflammation, growth and reproduction. Ingesting the structural trans-isomers of linoleic acid and alpha linolenic acid from hydrogenated vegetable oil provides the essential fatty acid pathways with a range of fatty acids that are structurally similar to linoleic acid and alpha linolenic acid, but which serve no cellular function and cannot be converted into the eicosanoids or docosanoids. These trans fats pass down the pathways and thereby inhibit the enzymes within it. The result is that eicosanoic formation is inhibited because both linoleic acid and alpha linolenic acid do not have access to the required converting enzymes.
Trans fats therefore interfere with essential fatty acid metabolism and cause imbalances in eicosanoid and docosanoid formation. The ability of trans fats to upset the fatty acid composition of cell membranes has been studies in animal models, and researcher have shown that they do indeed interfere with essential fatty acid metabolism1. The imbalances they cause lead to cellular changes that are detrimental to health. The health effects of trans fats are therefore very similar to those caused by an essential fatty acid deficiency, and include an increase in the risk of cardiovascular disease, obesity, type 2 diabetes, and cancer. The problem of trans fats is exacerbated by the fact that most Westerners already consume an unbalanced diet that creates a borderline essential fatty acid deficiency in most individuals. The presence of trans fats in the diet simply tips these people into a full deficiency leading to the slow and insidious development of all the typical Western lifestyle diseases.
Dr Robert Barrington#s Nutritional Recommendation: Trans fats have only relatively been identified as disease causing agents. In the past trans fats were either ignored in research or grouped together with saturated fats for convenience. This ignorance as to the biochemical effects of trans fats calls into question much of the early research linking saturated fat to cardiovascular disease, as unidentified confounding variables were clearly present. Trans fats have been a disaster for health, and although the United Stated government has passed legislation to remove them from the food chain, the United Kingdom government has given carte blanche to the food industry to continue the practice of incorporating partially hydrogenated fats into processed foods. The presence of trans fats is good enough reason alone to avoid anything that is processed and contains added vegetable oil.
RdB
