Fats are confusing. With so many different types it is very difficult to know which ones are good and which are harmful. Certain fats however, such as trans fats, have had bad press. But what is a trans fat? And what makes them so bad for us above other types of fats? In order to understand this, we need to have a basic understanding of the structure and function of fat.
What are fats made up of?
Fats are also known as lipids and are the most energy dense food substance available to us at 9kcal/gram (in comparison to carbohydrate and protein, both at 4kcal/gram). This holds true for all fats whether it is healthy olive oil or a lump of lard. All fats are made up of 3 elements; carbon, hydrogen and oxygen. Although they have the same elements, different fats vary in structure and therefore behave differently in our body.
Triglycerides make up approximately 90% of our dietary fat and the vast majority of fat in our body. When we have excess calories in our body, they are stored as triglyceride. They are made up of 3 fatty acids stuck onto a glycerol back-bone. Think of a letter E. The part of the triglyceride structure that needs our attention is the fatty acid. It is here where the battle of good vs bad fat begins.
With the knowledge that fatty acids (FAs) are made from carbon, hydrogen and oxygen lets look at the structure of each individual fatty acid in a little more detail.
Saturated fatty acids are packed full of hydrogen bonds with no double bonds, in other words have no more room left in the molecule. These fats are hard white and solid in their visible form e.g. the white coating found within meat. The physical properties of all fat is very dependent no their composition and temperature. The more hydrogen ions in the FA, the 'stiffer' therefore more solid the fat. in addition, the colder the saturated fat is, the more solid it becomes. Less visible saturated fats can be found in coconut oil, cheese and whole milk. These saturated fatty acids have been closely linked to heart disease, stroke and type 2 diabetes.
In contrast, unsaturated FAs do have double bonds in their structure. A mono-unsaturated fat has one double bond and poly-unsaturated fats have two or more. The double bond(s) create ‘space’ within the molecule with fewer hydrogen ions. This means that unsaturated fats are 'less stiff' a substance and typically liquid at room temperature. Examples include sunflower, safflower and olive oil. All the 'good for you' Mediterranean diet classics. Unsaturated fats have been shown to lower cholesterol and are 'heart healthy'. Omega 3 and 6 are also types of polyunsaturated fats.
Trans saturated fats
Tran fats are unsaturated fats that have been tampered with by a process called hydrogenation. This basically means blowing hydrogen ions through the fat to break the double bonds and pack out the FA molecule. Why would anyone want to do this I hear you ask? Hydrogenatingfat makes it more solid at room temperature and aids food preservation and storage. This is great for manufacturers who don't want their product to go bad and improve the shelf life of their products. It can also enhance the culinary property of the food.
An important distinction is between partial and fully hydrogenated fats. A partially hydrogenated fat, is what we refer to as trans fats. If the hydrogenation process continues then the FA becomes packed full or 'saturated' with hydrogen ions, and essentially becomes a saturated FA. Trans fats, like most saturated fats, raise blood cholesterol levels, particularly levels of ‘bad’ LDL cholesterol. Trans fats can also reduce the ‘good’ HDL cholesterol, as well as increase levels of another form of blood fat called triglycerides. All of these effects of trans fats can raise your risk of coronary heart disease (CHD). Gram for gram, trans fats appear to increase risk of CHD more than saturated fats, and so pose a greater risk for our health.
There has been speculation whether trans fats may also occur when ordinary vegetable oils are heated to fry foods at very high temperatures and this is one reason why takeaway foods can sometimes be high in trans fats. But the jury is still out on that one. Naturally occurring trans fats also do exist and are found in small amounts in dairy products, for example cheese and cream, and some meats.
All trans fats may be potentially unhealthy, no matter where they come from, but if they are present or consumed at low levels, they are unlikely to have a signicantly harmful effect.
Gram for gram, trans fats appear to increase risk of CHD more than saturated fats, and so pose a greater risk for our health.
Now you know what trans fats are all about, here are some simple steps you can take to reduce the amount of trans fats in your diet;
In summary, be aware of the daily requirements for all the different types of fat. NHS guidelines indicate that the average adult can eat up to 70g of fat a day, of which no more than 20g should be saturated and the rest (50g) unsaturated. Reducing your trans fat consumption to a minimum can only be good for your heart, weight and general health.
Look out for my blog on fish oils and cholesterol to explore the world of fat a bit further! Thanks for reading!