Understanding Fats

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 Let’s talk about Fats.


In my last post, I wanted to outline the role of protein in the body, and why it is important. Now let’s turn our attention to another of the macronutrients in Fat.


The role and importance of dietary fat is something that has had a substantial rethink in recent years. Categorised under organic compounds called lipids, part of the negative connotations surrounding fat centre on energy density. At 9kcal per gram, fats contain over double the number of calories to protein and carbohydrates. It was therefore reasonable to assume that limiting fat consumption would make it easier to reduce caloric intake. However, fat consumption does not make us fat. Consuming excess calories in comparison to energy output does. And demonising fat ignores the essential role fats play in our physiology. Specifically, fats are required for the formation of cell membranes and the transportation of vitamins; they constitute the majority of the central nervous system and spinal cord; protect organs, as well as store energy.


Fats and oils are categorised under the organic compound called lipids, and are made up of a carbohydrate backbone (glycerol) with three fatty acids attached to it, called a triglyceride. The structure of the fatty acid tail determines the type of fat. There are three main types of dietary fat, all of which have different chemical structures and effects on the body. These are: Saturated fatty acids (SFAs), Monounsaturated fatty acids (MUFAs), and Polyunsaturated fatty acids (PUFAs). Most fat rich foods will contain a mix of all three but will typically be higher in one type, which determines their physical properties. Fat sources higher in SFAs are solid at room temperature, whereas those higher in unsaturated fats tend to be softer or liquid.


SFAs primarily come from animal products, with the exception of palm oil and coconut oil, and are solid at room temperature. This is due to the fatty acid tails attached to the glycerol. These chains of carbon atoms are ‘saturated’ in hydrogen and their straight structure allows them to pack tightly together. This accounts for the solid structure at room temperature. Despite the negative assumptions that are made about the presence of SFA’s in the diet, it plays an important role in the immune system, and enhances liver function against toxins. Including SFAs as part of a balanced diet helps to mitigate any negative impact they can have in terms of coronary health.


Unsaturated fats (both MUFAs and PUFAs) are mainly found in plant products and are liquid at room temperature. This is due to the hydrogen being absent from the carbon atoms in the fatty acid tails, causing the tails to kink. MUFAs have a single bend in the tail, while PUFAs have multiple. Found in olive oil, avocados and nuts, our bodies are able to recognise the distinct shapes of these fatty acids and utilise them accordingly. Diets containing suitable amounts of MUFAs have been shown to lower harmful cholesterol and reduce the risk of heart disease.


PUFAs, meanwhile, are classified as Omega 3 and Omega 6 Fatty Acids and can be found in oily fish (omega 3), and a variety of seeds (Omega 6). These fatty acids are essential when controlling blood pressure, preventing clots, and the maintenance of the quality of cell membranes. Hence, the assumption that a diet high in Omega 3 and Omega 6 helps prevent decline while aging. An example of this often put forward would be the mediterranean diet.


All of these forms of fats are naturally occurring, and can be easily recognised by the body. However, there is another form of fat, which is heavily present in our diets that is not. Hydrogenated or trans fats are produced through a process of hydrogenation to manufacture an unsaturated liquid into a solid. This manufactured process adds hydrogen atoms to unsaturated double bonds, giving the fatty acid tail the appearance and characteristics of a solid saturated fat. Trans fats are therefore manufactured to look like saturated fat, but without being fully saturated. Our bodies, therefore, find it difficult to recognise and process these artificial fats, making them more likely to be stored. It is also these aspects which make trans fats detrimental to our health (among many other negative health aspects which I will cover in a future entry).


The final thing I want to discuss here is cholesterol. Cholesterol is a large fat molecule which is essential for life. Transported through the blood, it is used extensively throughout the body tissues for both structural and functional purposes. While it is a fat, because cholesterol is not used for energy purposes, it has very little calorific value. Cholesterol is produced in the liver and released into the blood. Because it does not mix well with the watery nature of blood, the cholesterol lipid is packaged with a carrier protein (a lipoprotein). These lipoprotein have three categories:

  • VLDL: Very Low Density Lipoproteins

  • LDL: Low Density Lipoproteins

  • HDL: High Density Lipoproteins

VLDL is synthesised by the liver and contains both cholesterol and triglycerides. LDL is formed from VLDL once they have unloaded most of their triglycerides, and transport the remaining cholesterol to the required cells in the body. HDL is synthesised by the liver and helps transport excess cholesterol from the tissues and blood back to the liver for reuse or excretion. In a healthy diet the activity of HDL’s and LDL’s work in an important balance. This is due to LDL’s depositing their excess cholesterol on the walls of arteries, and the build up of arterial plaque can lead to the coronary artery disease. High levels of LDL cholesterol can be caused by diets high in saturated and trans fats. However, in a properly balanced diet, the HDL’s work to ‘mop up’ this excess cholesterol. This is why measuring cholesterol has become such an important health factor. Maintaining a total cholesterol amount of <5.0 mmol/L (millimoles per litre), with a healthy upper limit of 5.2 mmol/L is important. Within this, 25% of the total cholesterol should be HDL to be classified as healthy (Heart UK:2012).


In summary, this is why maintaining the correct amount of fats in your diet is important, as well as avoiding an overreliance on hydrogenated fats. Government guidelines call for the fat intake of the majority of the population to be between 25-35%, and should be broken down to 11% SFAs, 13% MUFAs, and 6.5% PUFAs. This will help to maintain balance in the diet. Notice here how I have talked about dietary fat rather than body fat. Hopefully I have been able to show the distinction between the energy our body needs through consumption of specific fats, and how this differs from body fat (stored energy). In my next post I want to turn the attention to looking at the role of carbohydrates in more detail, but please leave any comments or questions in the comment section. I will also return to these themes in a future post. Especially considering the role of ultra-processing in our diets.

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