Should we worry about trans fats?

Author: Kirstie Lamb, Researcher and Trainer in Public Health/8 January 2018

It is well known that trans fats are bad for our health and that they are fats to avoid, but why is this the case? The aim of this blog is to explain what trans fats are, their use in food manufacturing, why they should be avoided and how we can try and limit their consumption.

What are trans fats?
Firstly, let’s discuss what exactly trans fats are. All fats are made up mainly of carbon and hydrogen atoms bonded together, with the addition of some oxygen atoms. Varying compositions of these atoms and structures determine the type of fat. Unsaturated fats have kinks in their chains, meaning that the chains of atoms cannot be packed together tightly, so they tend to be liquid at room temperature. For example, sunflower and olive oils. To make the oil more solid at room temperature (so that it can be used in specific food manufacturing processes), a process called hydrogenation is used to remove these kinks, ultimately straightening the chains. Hydrogenation involves extra hydrogen being added to unsaturated liquid fats, resulting in either full or partial saturation of the fat. This usually takes place by passing water or hydrogen gas through the fat and is the main form of processing when constructing trans fats.
Full hydrogenation means that all of the carbon atoms in the chain have the maximum number of hydrogen atoms attached (they are saturated). This removes the kinks and the chains can therefore be packed tightly together, meaning that the fat becomes solid at room temperature.
Partial hydrogenation means that, although additional hydrogen atoms have been added, there are still some carbon atoms that have not been bonded to their maximum number of hydrogen atoms. The fat that is produced is semi-solid at room temperature. It is these partially-hydrogenated fats that tend to be referred to as trans fats.
Figure 1. Structure of fats (Saturated, unsaturated and trans). Retrieved from:

Why have trans fats been used in the past?
When saturated fats were first demonised, food manufacturers looked for a similar alternative to use in their products. Oils aren’t always suitable for manufacturing purposes; hence the need for a more ‘stable’ alternative. This alternative was artificially-made trans fats. Trans fats are a cheap substitute, whilst the hydrogenation process helps to increase the shelf-life of the fat. It is also easier to manipulate the physical properties of the fat, such as the hardness and melting point, through controlling the degree of hydrogenation that takes place. Trans fats have also been found to mix well with flour, creating an appealing texture when used in the production of baked products.

Why should we avoid consuming trans fats?
Despite products containing these hydrogenated fats initially being promoted as a healthier alternative to saturated fats, many health concerns have since been associated with the consumption of these fats. Hydrogenation involves heavy processing, the use of high temperatures and pressure and other processes that change the chemical structure of the fats. This processing can also damage the fat molecules.
Some studies have demonstrated that increased consumption of trans fats leads to an increase in the number of small dense LDL (the cholesterol transporters in our bloodstream that are more prone to damage and dropping their cholesterol), a reduction in the number of HDL (cholesterol carriers that help ‘sweep’ away any excess cholesterol to the liver) and an increase in triglycerides (fats) in our bloodstream (Mensink and Katan 1990, Kleber et al. 2015). As these are all risk factors for many longer-term health complications, it should come as no surprise that evidence also links trans fats to the development of several health complications, including heart disease and obesity (SACN 2007, Mozaffarian 2009, de Souza et al. 2015, Liu et al. 2017). Furthermore, it has been suggested that an increase in trans fat consumption may also alter the function of our cell membranes, changing their composition and decreasing fluidity, which may have a negative impact on our health (Ibrahim et al., 2005).

Another negative of trans fats is that the oil used during the hydrogenation process tends to contain high amounts of polyunsaturated omega 6 fats (e.g. vegetable oils; read our previous blog here for more information). It is suggested that excessive consumption of these fats promote inflammation, especially when the ratio of omega 6 to omega 3 in our diet is high (Simopoulos and DiNicolantonio 2016).

Which foods contain trans fats?
Although trans fats can be found naturally in some foods, such as milk, lamb and beef, they are present in such small amounts that they need not be avoided. Additionally, it is argued that ‘naturally’ occurring trans fats are much less detrimental to our health than processed fats. These foods can also provide us with many other beneficial and essential nutrients, so can be included as part of a healthy diet. Instead, it is the manufactured partially hydrogenated fats that we should actively be avoiding. Foods containing these trans fats tend to be highly processed, for example some takeaways and margarines.
Many foods previously utilised trans fats as a way to promote a low saturated fat content in their products. For example, until the 1980s margarine often contained 10-20% trans fats. With increased recognition of the health concerns, many products (including many of these fat spreads), have since been reformulated by manufacturers to lower or remove trans fats. Other countries, including Denmark and Switzerland, have banned trans fats completely, potentially contributing to the reductions in CVD deaths observed in these countries (Restrepo and Rieger 2015).
The UK Scientific Advisory Committee on Nutrition recommends that average intakes of trans fats should remain below 2% of our energy intake (SACN 2007). Current intakes appear to be much lower than this on average, possibly owing to the reformulation of many products. However, it is still important to be aware of potential hidden sources and for individuals consuming more than the national average to reduce their intake.

How can you tell that a food contains trans fats?
Packaging may not always state that there are trans fats in the product, as there is currently no legal requirement for UK manufacturers to do so. However, if the nutritional information on the pa ckaging states that the product contains partially hydrogenated fats, this can suggest that trans fats are in fact present. The higher up the ingredients list this is, the more trans fats the product is likely to contain. The best way to avoid the consumption of these fats is to choose real foods rather than processed or refined products. Look at the ingredients list and choose products with fewer ingredients (e.g. vegetables tend to only have one ingredient!) and ingredients you recognise (i.e. not chemicals). Some takeaway places may still use trans fats in their products, as they are a cheap ingredient. Therefore, consider cooking takeaway-style meals from home instead, as you are then able to control what ingredients the meal contains!

de Souza, R. J., A. Mente, A. Maroleanu, A. I. Cozma, V. Ha, T. Kishibe, E. Uleryk, P. Budylowski, H. Schünemann, J. Beyene and S. S. Anand (2015). Intake of saturated and trans unsaturated fatty acids and risk of all cause mortality, cardiovascular disease, and type 2 diabetes: systematic review and meta-analysis of observational studies.
Kleber, M. E., G. E. Delgado, S. Lorkowski, W. Marz and C. von Schacky (2015). “Trans fatty acids and mortality in patients referred for coronary angiography: the Ludwigshafen Risk and Cardiovascular Health Study.” Eur Heart J.
Liu, A. G., N. A. Ford, F. B. Hu, K. M. Zelman, D. Mozaffarian and P. M. Kris-Etherton (2017). “A healthy approach to dietary fats: understanding the science and taking action to reduce consumer confusion.” Nutr J 16(1): 53.
Mensink, R. P. and M. B. Katan (1990). “Effect of Dietary trans Fatty Acids on High-Density and Low-Density Lipoprotein Cholesterol Levels in Healthy Subjects.” New England Journal of Medicine 323(7): 439-445.
Mozaffarian, A. a. W. (2009). “Health effects of trans-fatty acids: experimental and
observational evidence.” European Journal of Clinical Nutrition 63: 5-21.
Restrepo, B. J. and M. Rieger (2015). “Denmark’s Policy on Artificial Trans Fat and Cardiovascular Disease.” Am J Prev Med.
SACN (2007). SACN Update on Trans Fatty Acids.
Simopoulos, A. P. and J. J. DiNicolantonio (2016). “The importance of a balanced ω-6 to ω-3 ratio in the prevention and management of obesity.” Open Heart 3(2): e000385.

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