From fat shaming to fat fears, it's clear that we have a rather uneasy relationship with this important nutrient. In recent years, the certainty that all or some fats are bad for us has been challenged by studies showing that higher-fat diets are not necessarily damaging to heart health. Yet, dietary guidelines continue to recommend low-fat diets, leading to disagreements between nutrition experts.
What is fat?
'Fat' is actually the family name for a whole host of individual fatty acids. These are split into two groups - saturated and unsaturated - depending on key aspects of their structure.
Saturated fats are straight, dense chains of molecules and this characteristic makes them typically solid at room temperature. You can find saturated fats in animal products, such as butter, cream, lard, cheese and fatty meats, but also in vegetable products such as coconut fat and palm oil. Examples of individual saturated fatty acids include butyric acid, stearic acid and palmitic acid.
Unsaturated fats are less dense and have a bendy structure which makes them liquid at room temperature thanks to the presence of one or more double bonds holding the molecules together.
They are split into monounsaturated fats, which are particularly high in olive and rapeseed oils, and polyunsaturated fats, which are found in vegetable oils, fish oils, nuts and seeds. Examples of individual unsaturated fatty acids include oleic acid, linoleic acid and the so-called omega-3 fatty acids, linolenic acid, docosahexaenoic acid and eicosapentaenoic acid. Unsaturated fats are believed to be healthier options.
A third group, trans fats, only exist in tiny amounts in a few natural foods, such as ruminant meat (cows, sheep, goats, etc) and dairy products. However, in the 1970s, large amounts of trans fats were manufactured by changing the structure of unsaturated fats to force them to be solid at room temperature. These were then added to an array of processed foods such as margarine, cakes and biscuits.
In the last few decades, efforts have been made to minimise trans fats in products, due to concerns about their negative impact on blood cholesterol levels and heart disease risk. Intakes of trans fats in the UK have now reduced to half the maximum limit. There is no legal requirement to list trans fats on labels but you can check product ingredient lists for 'hydrogenated fats/oils' which may contain trans fats. Takeaway foods are also a source, as high temperature heating of vegetable oil boosts the trans fat content.
Which fats are healthy?
There is no need to fear dietary fat as it's essential for health. Fat provides energy, helps to keep us warm, cushions our vital organs, protects our body cells and acts as a carrier for fat-soluble vitamins, such as A, D, E and K. More than half of the brain is fat and our cognitive development and brain functions rely on essential fatty acids that can't be made by our bodies.
However, that said, it's worth remembering that fats are a rich source of calories, making them easy to overeat. As an example, one 50 g cube of cheddar cheese has the same calories as two medium bananas. Also, several high-fat foods, such as biscuits, cakes, confectionery, desserts and ice cream, are high in sugar too.
So, which types are the healthiest? Professor Philip Calder from the University of Southampton says: "Fats affect the way that cells and tissues in the body work. Some, like omega-3s, are better for us because they promote optimal cell and tissue function. Ultimately, this relates to improved well-being and less risk of disease."
According to Professor Calder, his top choice would be omega-3s from oily fish, although: "Plant omega-3s from nuts, especially walnuts, and monounsaturated fats like those in olive oil, are important too."
He is less enthusiastic about the fad for coconut oil and ghee adding: "Many cultures consume these regularly but there is little evidence that they actually have health-promoting properties. I would like to see more research on these fats before making a judgement."
Should we avoid some fats?
Apart from artificial trans fats, there's no need to cut out any particular fats from the diet. There is even doubt that saturated fats, which as a group were traditionally given the thumbs down by nutritionists, are as bad as we thought for cholesterol levels and heart disease.
The confusion may have arisen because scientists now know that individual saturated fatty acids have different effects on the body and are not one entity as previously believed. This means that some saturated fats, such as those found in dairy foods and lean red meats, could be fairly harmless. The issue is being examined by the UK's Scientific Advisory Committee on Nutrition so we should see more detailed advice on fats in the next year or two.
In the meantime, the best option is to rebalance our fats towards plant sources, choose lean meats, poultry and oily fish, and keep high-calorie fatty foods to a minimum.
Sian Porter, spokesperson for the British Dietetic Association, says: "In the UK we're still eating too much of the saturated fats found in cakes, biscuits, pies, pastries, confectionery and fatty meats so we need to cut down these foods."
She adds: "As for cooking, it depends on what you’re making but, in the main, try to use small amounts of unsaturated fats such as olive oil and rapeseed oil. Poor storage and constant reuse can change the fatty acids into harmful forms so always store your oils away from sunlight in a cool, dark place and replace regularly. Butter, ghee and coconut fat are fine to use occasionally in small amounts if you like the taste but there's no evidence that adding them to your diet offers any benefits."