Fulsome Fats

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Lipids (fats) provide essential nutrients in the diet in the form of essential fatty acids and fat soluble vitamins (A, D, E), whilst making the food we eat more palatable and tasty – “fat means flavour”. They are organic compounds formed from carbon, hydrogen and oxygen, mostly insoluble in water and together with carbohydrate and protein, one of the principal constituents of cells.

Fatty acids are the main component of dietary fat formed from long chains of carbon atoms (usually >14) and hydrogen atoms. Generally they are not found as free fatty acids and are often combined with glycerol – three fatty acids joining with glycerol create triacylglycerol (TAG), also known as triglyceride. 

Dietary TAG is broken down by bile salts and digestive enzymes in the gut and absorbed via the small intestine where it is reconstituted as TAG and packaged for transport as lipoproteins in the blood stream. TAG is either stored in adipose tissue or used as energy, for example in muscle cells. In more complex arrangements, fatty acids are key constituents of cell membranes (the phospholipid bi-layer) and also lipoproteins which transport lipid molecules in the blood, e.g. HDL and LDL (High Density Lipoprotein and Low Density Lipoprotein). The body is able to synthesise fatty acids within cells from one of the interim products of glucose metabolism, whilst fatty acids can be used to produce ketone bodies in the liver and act as an alternative energy source when glucose is in short supply.

Saturated and unsaturated fatty acids

In the fatty acid hydrocarbon chain, carbon can form four bonds with other atoms in the chain and hydrogen can form one bond. Figures 1 and 2 below give examples how this bonding occurs and the effects on the properties of fats:

Figure 1: Stearic acid – a saturated fatty acid

saturated fatty acid


The maximum number of hydrogen atoms are bonded to carbon atoms in the central chain.

The COOH group in red forms a bond with glycerol to create TAG (3 fatty acids + glycerol)

Fats which contain a high proportion of saturated fatty acids tend to be solid at room temperature.

Saturated fatty acids can be found in fatty meats and meat products, e.g. beef and lamb, bacon, burgers, sausages, pies; dairy products, for example whole milk, cream, ice cream, fat spreads, cheese; cereal products where fat is used as shortening, e.g. pizza, pastry, biscuits, cakes; foods cooked in saturated fats and coconut and palm oil.

Figure 2: Linoleic acid – an unsaturated fatty acid

unsaturated fatty acid


Fewer than the maximum number of hydrogen atoms are included in the chain. This is because some of the carbon to carbon links are double bonds.

One double bond in the chain denotes a monounsaturated fatty acid; more than one and it becomes a polyunsaturated fatty acid.

Fats which contain a higher proportion of unsaturated fatty acids tend to be liquid at room temperature and known as oils.

Monounsaturated fatty acids occur in olive oil, rapeseed oil, nuts and seeds, avocados and some animal tissues.
Polyunsaturated fatty acids are found in oily fish, for example salmon, mackerel, tuna (omega-3 fatty acids) and sunflower oil, sunflower seeds and corn oil (omega-6 fatty acids). Most omega-3’s and omega-6’s are essential in the diet as the body is unable to synthesise them.

Saturated fat and health

There has been considerable research into the effects of saturated fats on health with conflicting results. In a 2019 report2, the government’s Scientific Advisory Committee on Nutrition published their findings following an in-depth study of randomised control trials, meta-analyses and sytematic reviews on the topic. Their overall conclusion is that a reduction in dietary saturated fat for adults and children over 5 (‘to no more than about 10% of [total] dietary energy’would be beneficial to reduce the risk of events related to coronary heart disease and cardiovascular disease. Based on available research, their findings indicate saturated fat be substituted with polyunsaturated fats, given more evidence is currently available to support this than substitution with monounsaturated fats.

Cholesterol, a vital component of cell membranes, is often mentioned in conjunction with fats. Whilst not a fat per se, it is commonly found in foods containing animal fat, i.e. saturated fat. A large proportion of cholesterol circulating in the bloodstream is synthesised by the liver, with a smaller contribution from dietary fat. More information on cholesterol is coming soon.

Fats and energy provision

TAG is much more energy dense than carbohydrate and protein. The complete metabolic breakdown of TAG yields approximately 37 kilojoules per gram of TAG, which is almost 9 kilocalories per gram. This is in contrast to protein and carbohydrate which yield approximately 17 kilojoules per gram or 4 kilocalories3.


  1. Epomedicine. Structure of Fatty acids and Derivatives : Simplified [Online]. Epomedicine; Jul 29 2018 [viewed Mar 16 2021]. Available from: https://epomedicine.com/medical-students/structure-of-fatty-acids-and-derivatives-simplified/
  2. Scientific Advisory Committee on Nutrition (SACN). Saturated fats and health, 2019 [viewed 23 March 2021]. Available from: https://www.gov.uk/government/publications/saturated-fats-and-health-sacn-report
  3. Mathews, C.K. and van Holde, K.E. Biochemistry. California: Benjamin Cummings, 1990.

1 thought on “Fulsome Fats”

  1. Fulsome Fats! Essential nuritrents, Avocado etc…. understanding the science behind TAG & introducing more foods that help you feel full for longer, is the trick! The long term health benefits far outway the problems being stored up by saturated fats in our diets.

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