How do fats differ?
Most of the fats we eat have a similar, yet different chemical structure. They are made up of three fatty acids, known as a triglyceride, attached to a glycerol molecule. How they differ is down to their size (number of carbons in a chain) and structure (number or lack of double hydrogen bonds). It is these differences that affect how we metabolise and use fats and how they impact our health.
We commonly group individual fatty acids according to their structure or number of double bonds they contain:
- Saturated – no double bonds
- Mono-unsaturated – one double bond
- Poly-unsaturated – more than one double bond
It is well known that saturated, monounsaturated and poly-unsaturated fats each have different health effects, but less well-known is that individual fatty acids within these groups have distinct properties, too. This relates to their size (number of carbons in a chain) and is what we refer to when we talk about short-chain, medium-chain and long-chain fatty acids.
Most of us have been brought up with the idea that saturated fat is ‘bad’ while unsaturated fat is ‘better’ – or even ‘good’. However, more recent research suggests that we may have been unnecessarily demonising saturated fats.
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What is saturated fat?
Found in red meat, butter, cheese, ghee, burgers and sausages, as well as coconut and palm oils, a diet high in these fats has, for a long time, been thought to play a part in the development of obesity, heart disease and type 2 diabetes.
However, we now know that the various chain lengths (long, medium and short) of saturated fatty acids are relevant to how the fat affects our health, especially when it comes to our heart. For example. the structural differences between the medium- and shorter-chain fatty acids allow them to be digested and metabolised differently to the longer-chain ones, and as a result have less of a detrimental effect on our health.
Sources of medium-chain fats (6-12 carbons long) can be found in coconut oil, milk fat and palm oil, while short-chain fatty acids (2-5 carbons long) are found in butter – although these short chain fats are largely byproducts of fibre fermentation in our gut. That said, much of the saturated fat we eat tends to be the long-chain (over 13 carbons long) variety, found in meat, sausages and bacon, butter and lard, cakes, pies and palm oil.
Is saturated fat unhealthy?
For decades, the health community has presented saturated fat as a major risk factor for the development of cholesterol and heart disease. The demonisation of saturated fat was based on the theory that it raised the type of cholesterol known as Low Density Lipoprotein (LDL), which was thought to block arteries and increase the risk of heart attack and stroke. However, we now know that the cholesterol picture is much more complex than we first thought and, although saturated fat may raise a type of large LDL, this type is not as strongly associated with heart disease as the smaller, denser form of LDL cholesterol.
Although this and other new evidence suggests that saturated fat may not be directly linked to heart disease, it remains important to monitor your total fat intake. This is because most UK adults eat too much fat, especially saturated fat, and the evidence remains controversial. For this reason, the UK Government recommends total fat intake should not exceed 35 per cent of our total daily energy (calorie) needs with the maximum for saturated fats being 11 per cent of our total daily energy (calorie) needs.
Overall, should you avoid saturated fat?
Saturated fat has had a bad rap, but what the science is now telling us is that we need to consider saturated fats as a group of fatty acids with varying effects on our health and metabolism, rather than as a single nutrient. Nevertheless, with more research needed in this area, current guidelines remain unchanged and we are advised to limit our intake of saturated fat and, where appropriate, replace it with the unsaturated varieties such as those found in oily fish, olive oil, nuts and seeds.
One way to keep a check on the amount of fat you are eating is to get into the habit of reading labels. Turn to the ‘nutritional panel’ found on the back of the pack and run your finger down the per 100g column to the ‘total fat’ and ‘of which saturates’. Look to see if the product is high, medium or low in fat by checking to this handy guide:
High total fat = more than 17.5 g fat per 100g
Medium total fat = 3.1g-17.5g fat per 100g
Low total fat = 3g fat or less per 100g
High sat fat = more than 5g of saturates per 100g
Medium sat fat = 1.6-4.9g saturates per 100g
Low sat fat = 1.5g or less of saturates per 100g
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This article was last reviewed on 23 October 2023 by Kerry Torrens, registered nutritionist.
Kerry Torrens is a qualified Nutritionist (MBANT) with a post graduate diploma in Personalised Nutrition & Nutritional Therapy. She is a member of the British Association for Nutrition and Lifestyle Medicine (BANT) and a member of the Guild of Food Writers. Over the last 15 years she has been a contributing author to a number of nutritional and cookery publications including BBC Good Food.
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